i$A$ ^ X**1 ■ X^ *«l o S H'I°3H <* afiqnd 3JO)|a/V\ P"° £ 'uoitDsnpg 'tjliDaH * J° 4uaui|jodaQ g-fl -< g 2 pa o > z zo 5 > ce Belhesdo. Md US Deporlmenl of Heolll Z > 5 6 uo.103r.p3 Hl|°9H £ ,o luaajModag s n a pw opou^ag o.(o3np3 H,|oaH | }o .uaui.iodaQ c, n J pw op^^g > 3il k .X ** v ^ JtW x °* v .▲. ^x * a v a ^ -< ** tw^j ? f&\ o V V V ^\ <: 'VjJ? NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDIC 2 MrC X Q X. XSk 2 -J^t< X Q X >*9fc> 2 p. 3NiDia3w jo Aavaan tvnouvn 3NiDia3w jo Aavaan tvnouvn 3Nioiaaw jo Aavaan tvnoi -o NATIONAL LIBRARY OF MEDICINE N-* NATIONAL LIBRARY OF ^EDICI 3NIDIQ3 Sry'of medicine NATIONAL "B^YA°FSHOWN BEFORE LAST UAit MAR U1978 " 0 \9&5 WAR 3NIDIQ3W NAL LIBRARY OF MEDICI NATIONAL LIBRAR. wr MEDICINE NATIONAL LIBRARY OF MEDICINE NAT.ONAL LIBRARY OF MEDI 3NOI03W jo Aavaan ivnouvn 3nidiq3w jo Aavaan tvnouvn 3noiq3w jo Aavaan tvn .r'i MECHANICAL DENTISTRY. RICHARDSON. NEW DENTAL BOOKS AND NEW EDITIONS. HARRIS' DENTISTRY. Eleventh Edition. A complete Text-Book of the Principles and Practice of Dentistry, including Part I, Anatomy and Physiology ; Part II, Pathology and Therapeutics ; Part III, Dental Surgery; Part IV, Dental Mechanics. By Chapin A. Harris, m.d., d d.s., late President of the Baltimore Dental College. Eleventh Edition. Revised and Edited by Ferdinand J. S. Gorgas, a.m , m.d., d.d.s., Professor of the Principles of Dental Science, Dental Sur- gery and Dental Mechanism in the University of Maryland. With Two Full-page Plates and 744 other Illustrations. Octavo. 944 pages. Cloth, $6.50 ; Leather, $7.50. GORGAS' DENTAL MEDICINE. New Edition. Dental Medicine. A Manual of Dental Materia Medica and Therapeutics, for Practitioners and Students. By Ferdinand J. S. Gorgas, a.m., m.d., d.d.s., Professor of the Principles of Dental Science, Dental Surgery, etc., in the Dental Department of the University of Maryland. Second Edition, Revised and Enlarged. With Index of Diseases and Dental Formulary and General Index. Octavo. 379 pages. Cloth, $3.25. TAFT'S INDEX TO DENTAL LITERATURE. Being an Index to all the chief Dental Periodicals published in the English Language, 1839-1885, with a bibliography of the Periodicals. By Jonathan Taft, d.d.s , recently Professor of Operative Dentistry in the Ohio College of Dental Surgery, now Professor of Principles and Practice of Operative Dentistry in the Dental College of the University of Michigan, at Ann Arbor. Octavo. Cloth, $2.00. TAFT'S PRACTICAL TREATISE ON OPERATIVE DENTISTRY. The Fourth Revised and Enlarged Edition. 136 Illustrations. Octavo. Cloth, $4.25; Leather, $5.00. The rapid sale of the previous editions of this work is sufficient proof that the author did not over- estimate the wants of the profession for a work containing the principles of the science of Operative Dentistry, properly digested, methodized, and illustrated in such a manner as to be readily available to both practitioner and student. BARRETT'S DENTAL SURGERY FOR PRACTITIONERS AND STUDENTS. By Ashley W. Barrett, m.d., m.r.c.s., Surgeon-Dentist to, and Lecturer on Dental Surgery and Pathology in the Medical School of, London Hospital. 12mo. Illustrated. Cloth, $1.00. P. BLAKIST0N, SON & CO., Publishers, 1012 Walnut St., Pbilad'a. A PRACTICAL TREATISE MECHANICAL DENTISTRY JOSEPH RICHARDSON, M.D., D.D.S., LATE EMERITUS PROFESSOR OF THE PRINCIPLES OF PROSTHETIC DENTISTRY IN THE INDIANA DENTAL COLLEGE; FORMERLY PROFESSOR OF MECHANICAL DENTISTRY AND METALLURGY IN THE OHIO COLLEGE OF DF.NTAL SURGERY. '™Ofo i*C REVISED AND ENLARGED, WITH FOUR HUNDRED AND FIFTY-EIGHT ILLUSTRATIONS. PHILADELPHIA: P. BLAKISTON, SON & CO., No. 1012 Walnut Street. 1886. WU 186;' Entered according to Act of Congress, in the year 1886, by P. BLAKISTON, SON & CO., In the Office of the Librarian of Congress, at Washington, D. C. 1&0 THE MEMORY OF THE LATE JAMES TAYLOR, M.D., D.D.S., FORMERLY EMERITUS PROFESSOR OF THE INSTITUTES OF DENTAL SCIENCE IN THE OHIO COLLEGE OF DENTAL SURGERY, AS AN acknowledgment of professional eminence and private worth, BY HIS friend and former PUPIL, THE AUTHOR. PREFACE TO FOURTH EDITION. In the preparation of a fourth edition of the present work, the author has not been unmindful of the generous and favorable estimate placed upon those that have preceded it. A grateful appreciation of the distinction thus accorded the treatise has inspired the author with an earnest desire to render the work still more worthy of the confidence and patronage of the profession. Noting carefully the imperfections that revealed themselves on a studious and painstaking review of former editions, the necessity of a thorough revision of the whole body of the original text became apparent, and though this involved extended research and much labor, neither have been spared in the effort to render the present revised edition as faithful an exponent as possible of the best thought of the profession concerning the subject-matter of which it treats. In the work of expurgation and amendment the author has been materially aided by the friendly, impartial, and judicious criti- cisms to which former editions have been subjected. It would be impracticable to particularize the emendations and supplemental matters incorporated in this edition, since they permeate almost the entire body of the original matter contributed by the author, and can only be appreciated or estimated by a comparison of the present with previous editions. Some modifications in the arrangement and treat- ment of subjects have been introduced, as well as some later processes which have not heretofore been considered. In some unimportant particulars the sources of information made available by the author may not have been specifically vii Vlll PREFACE TO FOURTH EDITION. indicated, but, in general, the author has taken scrupulous care to accord the proper credit whenever this has been deemed necessary. Such acknowledgments will be found in their appropriate places throughout the body of the work. For esteemed personal favors and courtesies, the author's thanks are, in an especial manner, due to Drs. Seabury, of Providence, R. I.; Rollins, of Boston, Mass.; Litch, How, Essig, Bennett, Tees and Dixon, of Philadelphia, Pa.; Low and Matteson, of Chicago, 111., and Land, of Detroit, Mich. The author would also express his obligations to the S. S. White Dental Manufacturing Co.; Johnson & Lund, and Gideon Sibley, of Philadelphia; the Buffalo Dental Manufac- turing Co.; and Ransom & Randolph, of Toledo, Ohio, for illustrative cuts, and valuable and essential material not otherwise readily obtainable. Trusting that the present volume may be found to reflect, with reasonable fidelity, the present advanced state of the department to which it relates, it is respectfully submitted to the profession. J. Richardson. Teebe-Haute, Ind., October, 1886. PREFACE TO FIRST EDITION. In the preparation of the following treatise, the author has endeavored to present, in as concise and methodical a form as possible, the material facts and principles which relate to the Mechanical Department of Dental Practice in its present ad- vanced condition. In the accomplishment of this undertak- ing, the primary and leading purpose has been to furnish the student and more inexperienced practitioner with a practical guide to the manipulations of the laboratory, with accompany- ing elucidations of the elementary principles which underlie the practice of this important specialty. In furtherance of this design, all matters, discussions, and commentaries, not strictly material, have been carefully excluded. The arrangement and treatment of the various subjects embraced are such, it is believed, as will best facilitate the student in the acquisition of a knowledge of the department alluded to, and the practitioner in the intelligent and suc- cessful conduction of the manipulations which appertain to this branch of Practical Dentistry. In the belief that these objects have been mainly accom- plished, the work is respectfully submitted to the profession. J. Richardson. Cincinnati, Ohio, October, 1860. IX CONTENTS. PAGE Dedication, ......................... x Preface,.............................vii Introduction, .......................... 17 PART FIRST. METALS EMPLOYED IN DENTAL LABORATORY OPERATIONS, WITH PRELIMINARY OBSERVATIONS ON FUELS, AND THE VARIOUS APPLIANCES USED IN GENERATING AND APPLYING HEAT. CHAPTER I. FUELS. Liquid Fuels,..........................23-34 Sweet Oil,.........'.................. 23 Lard or Lamp Oil,....................... 23 Kerosene Oil, ......................... 24 Alcohol,............................ 24 Solid Fuels, ........................... 25 Wood,............................ 25 Bituminous or Pit Coal,...................... 25 Charcoal, ........................... 25 Coke,....................... -..... 27 Anthracite,.......................... 28 Gaseous Fuels,.......................... 31 Illuminating Gas, ....................... 31 Olefiant Gas and Gasoline,.................... 33 CHAPTER II. Appliances used in the Geneeation and Application of Heat, . 34-78 Lamps,............................ 34 Oil Lamps,........................34-35 Alcohol and Kerosene Lamps,...............35-37 Burners,...........................37-40 Bunsen's Original Burner,.................. 37 Blowpipes,........................... 40 Mouth Blowpipes,..................... 41 Bellows Blowpipes,..................... 45 Hydrostatic Blowpipes,................... 50 xi xii CONTENTS. PAGE Supports,.......................... *** Furnaces,........................... 55 Draught or Wind Furnace,................ 55 Hard Fuel Baking Furnaces,................56-59 Gas Baking Furnaces,...................59-69 Land's, ........................ 60 Rollins',........................ 66 Ferrier's,....................... 69 Gas Crucible Furnaces,............'•.....69-74 Heaters,.........................75"76 Ladle Furnace,....................... 76 Crucibles,..............;............ ^7 CHAPTER III. Metals Employed in Dental Laboeatoey Opeeations,.....78-134 Gold,............................78-85 Geological Situations,.................... 78 Geographical Distribution, ................. 79 Properties of Gold,..................... 79 Properties of Particular Alloys of Gold,........... 81 CHAPTER IV. Refining Gold,.........................85-91 Elements Employed,...................... 85 Separation of Foreign Metals from Gold,............. 86 CHAPTER V. Alloys of Gold foe Dental Pueposes,.............91-104 Reducing Metals,......................... 91 Required Fineness of Gold Plate,................ 91 Formulas for Gold Plate Used as a Base for Artificial Dentures, ... 92 Formulas for Gold Plate Used for Clasps, Wire, Stays or Linings, Metal Pins, etc.,.......................... 93 Gold Solders, Formulas for,..................94-95 Method of Reducing Gold to a Lower or Higher Standard of Fine- ness, and of Determining the Carat of any Given Alloy,..... 96 Table of Coinage of Different Nations,.............. 99 CHAPTER VI. Method of Conveeting Gold Alloys into the Requieed Foems foe Dental Pueposes,...................104-113 Manner of Procuring an Ingot,..........,...... . 104 Forging,............................106 Laminating or Rolling,.....................107 CONTENTS. Xlll PAGE Thickness of Gold Plate Required as a Base for Artificial Dentures, . 110 Thickness of Plate for Clasps, Stays, etc.,.............110 Reduction of Gold Solders into Proper Form for Use,........110 Method of Obtaining Gold Wire,.................110 Method of Constructing Spiral Springs,..............112 CHAPTER VII. SILVER,............................113-118 General Properties of Silver,...................113 Alloys of Silver,.........................113 Refining Alloys of Silver,....................114 Dry Method,........................114 Wet Method,........................115 Reduction of Silver to Required Forms for Dental Purposes, .... 116 Formulas for Silver Solders,...................117 CHAPTER VIII. Platinum and the Platinoid Metals,............118-122 Platinum,...........................118 Alloys of Platinum, ....................120 Platinoid Metals,........................120 Palladium,.........................120 Iridium,..........................121 CHAPTER IX. Aluminum,..........................122-126 General Properties of Aluminum,................122 Alloys of Aluminum,......................124 CHAPTER X. Coppee, Zinc, Lead, Tin, Antimony and Bismuth,......126-132 Copper,............................126 Alloys of Copper,......................126 with Zinc,.......................126 with Tin,.......................127 Zinc,.............................128 Lead,.............................128 Alloys of Lead,......................129 Tin,..............................129 Antimony,...........................130 Bismuth,...........................130 CHAPTER XL General Properties of Alloys, and theie Teeatment and Be- havior in the Process of Compounding,..........132-136 XIV CONTENTS. PART SECOND. ARTIFICIAL DENTURES. CHAPTER I. PAGE Treatment of the Mouth Peepaeatoey to the Insertion of Artificial Dentuees,...................136-142 Useless and Diseased Remains of Teeth,.............137 Removal of Salivary Calculus or Tartar,.............138 Diseased Conditions of the Mucous Membrane and Gums, ... . . . 139 Caries or Decay of the Remaining Teeth,.............139 Surgical Treatment of the Mouth After the Extraction of Teeth, . . 139 Time Necessary to Elapse After the Extraction of the Teeth Before Inserting Artificial Dentures,.................140 CHAPTER II. Materials, Appliances and Methods Employed in Obtaining Impeessions of the Mouth,.................142-180 Beeswax, ...........................146 Manner of Obtaining an Impression of the Mouth in Wax for Partial Upper Dentures,....................146 Manner of Obtaining an Impression of the Mouth in Wax for Partial Lower Dentures,.................151 Manner of Obtaining an Impression of the Mouth in Wax for Entire Upper Dentures,..................153 Manner of Obtaining an Impression of the Mouth in Wax for Entire Lower Dentures,..................155 Modeling Composition,.....................156 Gutta-percha,.........................156 Plaster-of-Paris,........................158 Manner of Obtaining an Impression of the Mouth in Plaster for Partial Upper and Lower Dentures,............166 Dr. Essig's Method,...................167 Dr. Austen's Method,..................168 Dr. Spence's Method,..................169 Dr. Litch's Method,.................. 172 Dr. Bennett's Method,................ 173 Dr. Dixon's Method,..................173 Manner of Obtaining an Impression of the Mouth in Plaster for Entire Upper Dentures,..................175 Manner of Obtaining an Impression of the Mouth in Plaster for * Entire Lower Dentures,..................178 CONTENTS. XV CHAPTER III. PAGE Plastee Models,.......................180-188 Manner of Obtaining a Plaster Model from an Impression in Wax, Gutta-percha or Modeling Compound for Partial Dentures, .... 180 Manner of Obtaining a Plaster Model from an Impression in Wax, Gutta-percha or Modeling Compound for Entire Dentures, .... 182 Manner of Obtaining a Plaster Model from an Impression in Plaster for Partial Dentures,.....................184 Manner of Obtaining a Plaster Model from an Impression in Plaster for Entire Dentures, .....................186 CHAPTER IV. Metallic Dies and Countee-Dies,..............188-205 Metallic Die,..........................188 Manner of Obtaining a Metallic Die,.............188 Molding, .......................188 Dipping, .......................195 Counter-Die,..........................196 Essential Properties of a Die,..................198 Table of Fusible Alloys, ....................203 CHAPTER V. PARTIAL DENTURES. Root Crowning,.......................205-325 General Reflections on the Method,................205 Conditions Modifying the Success of the Operation,........206 Preparation of the Root,.....................208 Fitting the Crown,......................212 Attaching the Crown by means of Wood Dowel-Pins,.......213 Dowel-Pins of Metal and Wood,.................216 Author's Methods in the Use of Rubber,.............217 Plate Attachment,.......................220 Dr. Darby's Method,....................220 Dr. Webb's Method, ....................221 Gold Crowns, .........................224 Dr. Morrison's Method,...................225 Dr. Beers' Method,.....................226 Dr. Talbot's Method,....................226 Dr. Case's Method,.....................227 Author's Method, .....................231 Cast Gold Cap or Articulating Face for Gold Crowns,........233 Methods of Securing Outline of the Dimension and Contour of the Root to be Banded,......................233 Dr. Harper's Method,....................233 Xvi CONTENTS. PAGE Dr. Baker's Method, Described by Dr. Barrett,........234 Gold Crown Faced with Porcelain,................234 Dr. Webb's Method,....................235 Dr. Weston's Method,....................237 Dr. Low's Method,.....................242 Dr. How's Method,...................254-261 Banded or Ferruled Crown Faced with Porcelain,.........264 Dr. Richmond's Method,..................264 Dr. Chappell's Method,...................267 Dr. Biittner's Method,....................268 Dr. Matteson's Method,'...................271 Dr. Litch's Method, Collar Crown,..............275 Dr. Leech's Method,....................282 Dr. Hunt's Method,.................... 283 Author's Method, Rubber or Gold Band,...........289 All-Porcelain Crown,......................291 Dr. Moffat's Method,....................248 Dr. Bonwill's Methods ,.................291-304. Dr. Gates' Method,.....................313 Dr. Logan's Method,....................319 CHAPTER VI. Beidge-Woek, Peemanent,..................325-398 Introductory Remarks,.....................325 Dr. Webb's Methods,....................326 Dr. Darby's Method,....................337 Dr. Litch's Methods,..................339-346 Dr. Register's Method,...................350 Dr. Williams' Methods,.................352-360 Dr. Low's Method,.....................370 S. S. White Dental Manufacturing Company's Method, .... 386 Beidge-Woek, Removable,..................378-398 Dr. Dexter's Method,....................378 Dr. Starr's Method,.....................383 S. S. White Dental Manufacturing Company's Method, .... 392 CHAPTER VII. Partial Dentures Retained in the Mouth by Means of Clasps Attached to the Natueal Teeth,.............398-418 Remarks on the Use of Clasps,..................398 The Teeth Most Suitable for Clasping,..............400 Separation of the Teeth by Filing for the Reception of Clasps, .... 402 Modifications in the Form of Clasps,...............403 Plain Band,........................403 Standard Clasp, ......................404 CONTENTS. xvii PAGE Scalloped Clasp,......................405 Partial or Stay Clasp.....................406 Modifications in the Form of Plates for Partial Dentures Supported by Clasps, ...........................406 Swaging or Stamping the Plate,.................411 Uniting the Plate and Clasps,..................413 CHAPTER VIII. Paetial Dentuees Suppoeted in the Mouth by Means of Cylindees of Wood Attached to Tubed Plates,......418-421 CHAPTER IX. Removable Paetial Dentuees Suppoeted in the Mouth by Attaching the Plate to the Roots of the Natueal Teeth, 421-424 CHAPTER X. Paetial Dentuees Suppoeted in the Mouth by Atmospheeic Peessuee oe Adhesion,...................424-428 Modifications in the Form of the Base,..............424 Manner of Forming a Vacuum Chamber,.............426 CHAPTER XL Method of Obtaining an Antagonizing Model foe Partial Dentuees ; Selecting, Aeeanging, and Antagonizing the Teeth ; Investing, Adjusting Stays, Soldering, etc., . . . 428-444 CHAPTER XII. Entiee Dentures, .....................• 444-465 A Consideration of the Principles and Attendant Phenomena In- volved in the Application of the Forces Utilized as a Means of Attachment,.........................444 Adhesion,...........................444 Atmospheric Pressure,.....................445 ^Esthetic Requirements in the Selection and Arrangement of the Teeth of Replacement,.......................452 The Four Basal Temperaments and their General Indications, Pre- sented in Tabular Form by Dr. J. Foster Flagg,.........455 The Teeth as Indicated by Temperament, Presented in Tabular Form by Dr. J. Foster Flagg,....................456 "•Temperament in Relation to the Teeth," by Dr. J. W. White, . . 57 xviii CONTENTS. CHAPTER XIII. PAGE Entiee Dentuees Attached to a Swaged Metallic Base-Plate, 465-494 Method of Constructing an Entire Upper Denture Mounted on a Swaged Metallic Base-Plate,..................465 Modifications in the Form of Plates for Entire Upper Dentures, ... 467 Method of Constructing an Entire Lower Denture Mounted on a Swaged Metallic Base-Plate,..................471 Antagonizing Model for an Entire Upper aud Lower Denture.....473 Antagonizing Model for an Entire Upper Denture with the Natural Teeth of the Lower Jaw Remaining,..............476 Bonwill's "Anatomical Articulator,"...............477 Arranging and Antagonizing the Teeth,..............482 Forming a Rim to the Plate,...................486 Constructing and Attaching Spiral Springs,............488 Investing, Lining, Soldering and Finishing the Plate,.......489 CHAPTER XIV. Poecelain Teeth,......................494-499 Components of Dental Porcelain,.................495 Silex,...........................495 Felspar,..........................495 Kaolin,..........................496 Coloring Materials,.......................496 Manufacture of Porcelain Teeth,.................497 Caeved Block-Teeth,.....................499-519 Composition and Preparation of the Body,.............500 Composition and Preparation of Crown Enamels,.........501 Composition and Preparation of Gum Enamels,..........503 Antagonizing Model for an Entire Upper and Lower Denture Con- structed of Block-Teeth,...................504 Antagonizing Model for an Entire Upper Denture with Lower Teeth Remaining,.........................504 Forming a Matrix for Molding the Body Preparatory to Carving the Teeth,............................506 Carving the Teeth,.......................510 Crucing or Biscuiting,......................511 Application of the Crown and Gum Enamels,...........511 Final Baking,.........................512 Fitting and Attaching the Blocks to the Metallic Base,.......513 Dr. Calvert's Method,......................515 CHAPTER XV. Uniting Single Poecelain Teeth to each othee and to a Metallic Base with a Fusible Silicious Compound, Forming a Continuous Aetificial Gum,...............519-553 CONTENTS. XIX PAGE Introductory Remarks,.....................519 Constructing Base-Plate, ....................520 Dr. Hunter's Method,....................522 Dr. Verrier's Method,....................523 Dr. Land's Improved Teeth for Continuous-gum Work, ......525 Dr. Allen's Modes of Practice,..................526 Dr. Hunter's Formulas and Modes of Practice,..........533 Dr. Haskell's Modes of Practice,.................540 Dr. Field's Modes of Practice,..................544 Dr. Tees' Modes of Practice and Formulas,............547 Application of Continuous Gum to Partial Sets,..........549 CHAPTER XVI. Vulcanite Base,.......................553-625 Introductory Remarks,.....................553 General Properties of India-rubber,...............553 Compounding Rubber for Dental Purposes,............555 Method of Constructing an Entire Denture in a Base of Rubber, . . 555 Arranging the Teeth,......................556 Formation of the Mold or Matrix,................560 Packing the Mold,.......................564 Vulcanizing,..........................573 Finishing,.......................... . 608 Partial Dentures Constructed in a Base of Rubber,.........608 Metallic Clasps Attached to Rubber Plates, . . ..........610 Substitution of Plate for Rubber Teeth, . . ...........611 Repairing,...........................612 Refitting Gold or Rubber Plates with Rubber Lining,.......620 Manner of Duplicating Sets of Teeth Mounted on Rubber,.....622 CHAPTER XVII. Celluloid Base,.......................625-662 Introductory Remarks,.....................625 Composition and Manufacture,..................626 Processes Preliminary to Molding,................627 Plaster Model,.........................627 Waxing or Modeling,......................629 Investing............................630 Selection and Preparation of the Celluloid Blank,.........633 Molding, ...........................635 Molding in Moist Heat,.....................635 Molding in Glycerine,......................639 Molding in Steam,.......................640 Molding in Dry Heat,......................645 XX CONTENTS. PAGE Dr. Spence's Experiments with Celluloid in Connection with the "New Mode Heater,"........................649 Repairing,...........................655 Vulcanite Base-Plate Faced with Celluloid,.........657 Zylonite,.............................661 CHAPTER XVIII. Attaching Poecelain Teeth to a Metallic Base with Rubbee oe Celluloid, .......................662-669 CHAPTER XIX. Cast Metal Base,......................669-681 Gold Alloy Cast Base,.....................672 Dr. Reese's Method,......................672 CHAPTER XX. Defects of the Palatal Oegans and theie Teeatment by Aetificial Means,.....................681-703 Dr. Kingsley's Artificial Velum and Palate,............681 Palatine Defects,.........................681 Obturators,..........................682 Artificial Palates,........................685 Artificial Palates for Congenital Fissure,.............691 Method of Making an Artificial Palate,..............693 A TREATISE ON MECHANICAL DENTISTRY. INTRODUCTION. Before entering upon a detailed account of the agencies, pro- cesses and methods appertaining to the department of dental practice to which this work relates, some general reflections may not be inappropriate. It is not the purpose of the author to unduly magnify the claims of prosthetic dentistry upon the regard and consider- ation of the profession. A just estimate of the nature of its requirements, and the momentous results contemplated in its practice, as well as the abundance and sufficiency of its resources in the accomplishment of its high and humane purposes, will, it is believed, amply vindicate its importance, its possibilities, and its eminent beneficence as a department of practical dentistry having intimate relation to the necessities of the unfortunate. The untimely or premature loss of the natural teeth may be ascribed to a number of diverse causes. Multitudes are lost in consequence of abuse or neglect, or the dread of pain so commonly associated with the means employed in their preser- vation ; many from unavoidable accident; and countless num- bers are sacrificed through the incompetency and dishonesty of ignorant and unscrupulous parties who, in one guise or another, infest and prey upon communities. Nor can we exclude from this list of causes another source of loss which, by implication, declares the impotence of the pro- fession's curative resources in the absolute conservation of these important organs. Whatever sense of humiliation may attend 17 18 MECHANICAL DENTISTRY. the statement, it is nevertheless true that the highest attainable skill directed to the permanent preservation of the natural teeth must, in the very nature of things, often prove inadequate and abortive, for no proposition is more broadly or more generally recognized by intelligent practitioners than that conservative practice has its limitations growing out of conditions associated with individual organisms and environments wholly beyond the control of the operator. Whatever triumphs (and they are many and conspicuous) modern conservative dentistry may have achieved in the way of narrowing the field of prosthetic practice, the prophecy, born of hope, that the time will come when the utmost resources of human skill will, in respect of the teeth, be able to exempt mankind wholly from the penal- ties of transgressed law, is as Utopian and delusive as the faith that prophylactic or preventive medicine will ultimately eradi- cate every form of disease that at present afflicts mankind. They are alike the idle dreams of enthusiasts and visionaries. Physical infirmity, in one form or another, is the heritage of the race, and human skill, however well directed or conscien- tiously and intelligently administered, can do little more than assuage or mitigate the /' pains and penalties " of the primal curse that rests upon all. It is the peculiar and distinctive prerogative of prosthetic dentistry to devise and perfect means for the amelioration of the condition of those who, from whatever cause, have suffered one of the gravest forms of mutilation, in the loss of organs so essential to the healthful performance of many important func- tions. In this special field of humane endeavor the highest order of qualification is imperatively demanded for the com- plete fulfillment of its diversified and complex requirements. No one can be said to be properly equipped for its duties who has not a more or less familiar acquaintance with such of the several branches of Physics and Natural Philosophy as .relate in any manner to his special work, while an exact knowledge of the Anatomy, Physiology and Pathology of the tissues or structures in any way related to the substitute is absolutely indispensable. Added to such qualifications is the essential requirement of the highest order of manipulative skill. But INTRODUCTION. 19 beyond all these qualifications, and supplementing them, is that art culture which is the crown and inspiration of all perfect work in every form of substitution, and without which the best results of mere handcraft are, in the main, but little better than libels and caricatures. In no other department of practical dentistry is the art instinct so strongly appealed to, or so impe- riously demanded as a condition of the highest success. Dr. Eben M. Flagg, in an essay on Dental Art, very aptly says: " There is an element which enters into the conception and exe- cution of every branch of our labor, and more or less forms part of every operation that we are called upon to make, be it surgical, operative or prosthetic. This element lightens our drudgery, enlarges our souls, gives individuality to our work, and brings satisfaction to ourselves that fully repays the time spent in fulfilling its requirements. It was born with our race, and has inseparably accompanied every movement that has brought comfort and happiness to man. It has contributed its share toward raising the physician from a mere 'bleeding, physicking, leeching' animal, to the position he occupies to-day, and has shown the mechanic and inventor that, if he would be great, he must be more than an artisan; he must be an artist. This element—the element of art—whenever it enters the field of human life, has for its function to finish and render attract- ive the hard labor that preceded it. Thus, we do not find it in its full manifestation except in those departments of labor which have attained scientific certainty." Among the unnumbered millions of human beings who have peopled the earth since the dawn of time, it may be affirmed that no two have been created with faces exactly alike. There is the same aggregate of features, and a pervading general re- semblance of one person to another, but there will be found as infinite a multiplication of distinct shades of facial expression as there are human faces, and each separate shade of expression characteristic of each one, and distinguishing him or her from all others, constitutes facial individuality. Each separate fea- ture—as the eye, the nose, the mouth, the teeth, facial contour, complexion, temperament, etc.—contributes to this individuality, and no one special feature more, perhaps, than the teeth. There MECHANICAL DENTISTRY. are few more repulsive deformities than those inflicted by the loss of these organs, and none more fatal to the habitual and characteristic expression of the individual. It is the special mission, as it is the first and highest duty, of the dentist to preserve this individuality intact, and an equally imperative duty to restore it as perfectly as possible when impaired. To fulfill, in the most perfect manner possible, this most difficult of all the requirements of prosthetic practice implies an art culture that is competent to interpret the distinct play of features associated with individual physiognomies, to differentiate indi- vidual temperaments, and make available the sculptor's and painter's perceptions of the subtle harmonies of form and color. To the failure or inability to properly comprehend the prac- tical import or significance of individual characteristics, so far as they find expression in the teeth, and the consequent failure to conform our methods of replacement to the imperative requirements of art, may be fairly ascribed the deserved reproach into which prosthetic practice has fallen, and not, as is generally charged, to the employment of any particular material or methods concerned in the mechanical execution of the work. There is no material classed among the so-called " cheap bases " that does not embody art possibilities far beyond what is being continually illustrated in general practice. Unques- tionably they are not the best for the purpose, but they may be greatly enhanced in value, and rendered more deserving of professional favor, if utilized in conformity with the sesthetic requirements imperatively demanded in all forms of substitu- tion. There is an ethical phase of this subject which must enter as an element into the profession's estimate of the suitableness of these inferior forms of replacement—a question of obligation and responsibility involving a problem the solution of which should be attempted without unreasonable prejudice or unjust discrimination, so far as materials and methods are concerned. There are multitudes in every community who, though not in indigent circumstances, are unable to secure expensive services without great hardship, and other multitudes who per- INTRODUCTION. 21 force must suffer lasting harm and prolonged deformity on the same terms. Dentistry, like Medicine, is professedly a humane calling, and it would be well to consider whether the afflicted have not just claims upon the profession's resources in provid- ing them with inexpensive means of relief. Until the time comes when the necessities of this class can be supplied with wholly unobjectionable forms of substitution at a cost that is not oppressive, or that does not altogether deny relief, it will be well to cease indiscriminate condemnation of materials and methods which, when properly considered in relation to their yet undeveloped possibilities, are far from being unmixed evils. That there are radical and inherent objections to the use of vegetable plastics that do not attach to metallic bases is unquestionable, but it is equally true that the nature, behavior, and proper or scientific treatment of these substances have not been, until quite recently, well understood; that imperfect ap- pliances have heretofore failed to develop their best qualities, and, above all, that there is a prevailing disregard or ignorance of all aesthetic requirements in the uses to which they are ap- plied. That the facility they afford for the ready construction of substitutes has attracted to the ranks of the profession a mercenary and unscrupulous class of operators, is as true as it is unfortunate. However powerless the profession may have been in the past to check this evil, the responsibility for its continuance in the future will rest largely with the profession itself. There is a reasonable assurance that the era of irre- sponsible quackery is fast passing away. The people of three- fourths of the States of the Union have, through their repre- sentatives, generously and confidingly relegated to the profession the power of providing a remedy for the evils of charlatanry, and have, under legal forms, designated our Colleges and Boards of Examiners as the proper custodians of the profes- sion's honor and the people's interests. A faithful execution of the trust reposed in these bodies will go far to redeem pros- thetic practice from the undeserved reproach brought upon it by a prostitution of its legitimate resources wholly unworthy of toleration and utterly destructive of all sense of professional self-respect. PART FIRST. METALS EMPLOYED IN DENTAL LABORATORY OPERATIONS, WITH PRELIMINARY OBSERVATIONS ON FUELS, AND THE VARIOUS APPLIANCES USED IN GENERATING AND APPLYING HEAT. CHAPTER I. FUELS. It is essential that the mechanical operator should have some intelligent conception of the nature and properties of such combustible substances as are ordinarily used in the dental laboratory for the generation of heat. This, with a somewhat familiar acquaintance wdth approved appliances used in the application of heat and adapted to his peculiar needs, are indis- pensable requisites to the successful practice of the department of practical dentistry to which this work relates. Only such heat-producing substances as are deemed suitable for dental laboratory operations will be considered with any degree of particularity. The general forms of fuel may be classified as Liquid, Solid, and Gaseous. They will be treated of, in more or less detail, under these general heads. LIQUID FUELS. In connection with lamps designed chiefly for soldering pur- poses, the combustible substances usually employed are, alcohol and oil. Among the oils, an excellent combustible is pure sweet oil, which has the advantage over kerosene of being abso- lutely free from danger of accident in its use. The common lamp or lard oil, however, is generally used for the purpose indicated, and, in the absence of other, in many respects, more desirable fuel, answers all practical requirements in minor ope- rations requiring the use of solder. Oil is used in connection with the lamps shown in Figs. 1 and 2. 23 24 MECHANICAL DENTISTRY. When alcohol, which is preferred by many on account of its greater cleanliness, and kerosene are used in soldering, a some- what different form of lamp is required. With one like that described for oil, there is. danger of explosion in the event of tire flame, mixed with air, communicating with the alcohol contained in the lamp, and which is more liable to happen when the spout is but loosely filled with wick. To provide against such an accident, it is not unusual to pack the wick too closely, which, by obstructing the flow of alcohol into the spout, lessens the heat of the flame. The proximity of the flame, also, to the body of the lamp, produces undue waste of alcohol by evaporation. The objections stated may be obviated by employing a lamp of either the forms shown in Figs. 3, 4, 5 or 6. With these lamps, the alcohol is uninfluenced by the heat of the flame, while explosion is rendered impossible. In the use of refined petroleum or kerosene, which is one of the products of the destructive distillation of crude petroleum, unusual precautions against such an accident are necessary. Good kerosene is always safe under all conditions attending its use, but its not infrequent contamination with naphtha, which is never safe under any circumstances, renders it violently explosive. No more than 5 per cent, will render kerosene inflammable at all ordinary temperatures, and liable to produce an explosion at any time when the vapors become mingled with air in proper proportion. The danger attending upon its use, therefore, may be better comprehended when it is remembered that there are those who manufacture and sell kerosene containing naphtha, and others who purchase the two, mix them, and sell them. A great deal of bad kerosene is placed upon the market, and con- sumed at great peril of life and property, and those who use it, therefore, would do well to apply to it the following test of purity: Take a pint tin cup, fill it nearly full of water warmed so that a thermometer immersed in it will show 120°, pour a small quantity of oil on the water, stir a little, then pass a lighted match quickly but closely over the oil once; if it ignites, the oil is unsafe. Good kerosene, uncontaminated with naphtha, may be used in the same manner as alcohol, and with equal FUELS. 25 safety, and is, in many cases, a valuable substitute for other combustible materials for general heating purposes, and is largely employed in connection with vulcanite and celluloid work by those unable to command the ordinary illuminating gas. SOLID FUELS. Under this head are comprehended such combustible sub- stances as are used for fires or draught furnaces, as wood, char- coal, bituminous and anthracite coal, and coke. For baking or muffle furnaces used in the construction of continuous-gum work and other allied processes, anthracite and coke are esteemed the most suitable, on account of the high temperatures attainable in their use, and the persistent or prolonged heat consequent on the comparatively slow waste of substance in the process of combustion. Wood, except when charred, is wholly unsuited for laboratory work. Bituminous,, or pit coals, are generally unfit for the uses required of fuel by the dentist, on account of the excessive carbonaceous residue accompanying their combustion, and are, therefore, seldom used except when reduced to that form of mineral charcoal known as coke. As charcoal, coke, or a mixture of the two, and anthracite coal are the heat-producing substances chiefly used in the processes of the dental laboratory requiring the employment of solid fuels, they will be more particularly described. Charcoal is the solid residuum of the destructive distillation of wood. It is obtained by igniting wood, and then excluding it from the air while burning; the volatile products are thus driven off, while the carbon remains. The chemical compo- sition of the ordinary charcoal of commerce is given in the following table, in which it will be seen to consist principally of carbon, combined with certain volatile constituents, a con- siderable percentage of absorbed water, and but little ash:— Carbon............ 70 Nitrogen.......... 1 Hydrogen.......... 5 Ash............ 2 Oxygen........... 11 Hydroscopic moisture .... 11 During the process of charring, the volatile constituents— 26 MECHANICAL DENTISTRY. hydrogen, oxygen and nitrogen—are, in a large measure, driven off, but no temperature that can be commanded, and no time, however prolonged, will wholly expel them. Charcoal is insipid and inodorous, is a poor conductor of heat and a good conductor of electricity, is insoluble in water, is attacked by nitric acid with difficulty, and is but little affected by the other acids or by alkalies. Its carbon constituent is exceedingly refractory to heat, and, if secluded in a retort, will neither fuse nor volatilize under the highest temperature that can be produced. This latter property of carbon, in connection with that of its comparative non-conduction of heat, makes it a valuable ingredient in the construction of supports used in soldering, represented in the carbon block and cylinder (Figs. 29, 30), and in the devices (Figs. 53, 54, 55) combining crucible and ingot mold. Charcoal retains the organic structure of the wood from which it was produced, except when prepared at very high temperature, when it becomes a black, shining, porous mass, resembling fossil coal, with a considerable increase in density and without a trace of organic structure. When it is desired to maintain a high heat in a small com- pass, the charcoal best adapted to the purpose is that obtained from what is termed hard wood, as the beech, the oak, the alder, the birch, the elm, etc. A cubic foot of charcoal derived from these woods weighs, upon an average, from twelve to thirteen pounds, while a similar bulk obtained from soft wood, as the fir, the different kinds of pine, the larch, the linden, the willowr and the poplar, averages only from eight to nine pounds.* There is, therefore, economy in the use of the former when purchased in bulk; and of this class the beech-wood charcoal is the best, on account of its greater specific gravity. Charcoals derived from the hard woods possess the additional advantage of generating a more equable and enduring temperature, and are, therefore, better adapted to operations in the laboratory requir- ing a prolonged heat. The more heavy charcoals require a stronger draught than those of a lighter character, as a more generous supply of oxygen is necessary to their perfect combus- tion. Charcoal should be kept as dry as practicable, since it *Ure. FUELS. 27 rapidly absorbs moisture from the atmosphere, by which its calorific energy is materially impaired. Coke.—This substance is a carbonaceous product obtained from bituminous coal that has been exposed to ignition for some time, excluded from the contact of air, the volatile con- stituents of the coal, like those of wood, having been driven off by the heat. There are two different varieties of this mineral charcoal, namely, gas coke, obtained from the retorts of gas works after the gases have been separated; and oven coke, which is made in ovens or pits, and which is considered by manufacturers as the only true coke, gas coke being merely cinder. There is a marked difference in the appearance of the two kinds of coke, the principal part of that obtained from gas houses being of a dull, iron-black color, very spongy and friable, is more rapidly consumed in the process of combustion, and produces less heat than the harder and more compact variety. The best coke for heating purposes is the oven or pit coke, which has a steel-gray color, with somewhat metallic lustre, is compact in structure, and splits into pieces having a longitudinal fracture. Whenever it can be procured, the latter should always be preferred in connection with the use of the baking or muffle furnaces employed in the fabrication of con- tinuous-gum work, porcelain teeth, etc. Until the more recent substitution of anthracite, the former was exclusively employed for these purposes, and is in every way suitable in the produc- tion of high and persistent temperatures. It is sometimes used combined with charcoal, but, when fairly ignited, gives an augmented and more lasting heat when used alone. Coke does not readily ignite, and at first generally requires the admixture of charcoal to effect its combustion; it also requires a strong draught to burn it, but when thoroughly ignited it produces an intense and persistent heat. As before stated, it is the principal fuel used in baking mineral teeth, porcelain blocks, and the silicious compounds employed in the construction of continuous-gum work. Professor Piggot, in his remarks on the comparative value of fuels, observes: "Practically, for the purposes of the chemist, the best fuel is charcoal or coke, or a mixture of the two. The 28 MECHANICAL DENTISTRY. ash of charcoal being infusible it passes through the bars of the grate as a white powder. Should potash, however, be in large excess it corrodes the bricks, by forming with them a silicate of potash, which runs down the walls and chokes the bars. In small quantities this action is beneficial, as it fur- nishes a protective varnish, and unites the bricks and lutes, by forming a sort of cement, which intimately combines with them. " Coke contains a very variable amount of ash, which is composed chiefly of oxide of iron and clay. The latter is not fusible by itself, but may soften. When pure it forms a harm- less slag, which injures neither the furnace nor the crucibles. Usually, however, the oxide of iron predominates. In this case the ash is very injurious, for it is reduced to a protoxide, which is not only fusible, but powerfully corrosive to all argillaceous matters, so that both the crucibles and furnaces suffer." * Anthracite.—Anthracite is the most condensed variety of mineral coal, containing the largest proportion of carbon and the smallest quantity of volatile matter. With the exception of the diamond, it is the purest form of carbon in its natural state. The best specimens contain 95 per cent, carbon, but the average production of the purest beds of this coal will not exceed 90 per cent., and generally not more than 80 to 87 per cent, carbon. The volatile matter in the dense, hard varieties is almost exclusively water and earthy impurities, but in com- mon varieties the volatile portion consists of water, hydrogen, oxygen, and nitrogen; while the ash or incombustible matter contains oxide of iron, iron pyrites, silica, alumina, magnesia, lime, etc. Anthracite which contains only 80 per cent, carbon, with 20 per cent, water and incombustible matter, is the lowest grade of commercial coal, and of little value as fuel. The general features and fractures of hard anthracite are peculiar and noticeable to the common observer. They are massive, hard, dense, amorphous or conchoidal in fracture, with fine, sharp edges when broken, and a rich satin or an iron-black sub-metallic lustre. With some local exceptions, * Dental Chemistry and Metallurgy, p. 274. FUELS. 29 the softer varieties, both red and white-ash (by which name the Pennsylvania anthracite coals are generally known), are less massive, hard and dense, more regular and cubical in frac- ture, and, exclusive of the upper red-ash beds, less rich and lustrous. Anthracite coals, in greater or less abundance, and of vary- ing qualities, are found in several of the States and territories of the Union, namely, in Pennsylvania, Massachusetts, Rhode Island, Virginia, Arkansas, Oregon, and in New Mexico and Sonora. Of the European anthracite fields, exclusive of those in Wales, England, the most prolific and largely developed are those in France, while others of more limited production are found in Spain, Portugal, Germany, Austria and Norway. Anthracite also exists in Persia, India, China and in South America. The most prominent anthracite fields of the world, however, are those of Pennsylvania and South Wales, which produce nine-tenths of the quantity used. The developed coal fields of the world embrace an area of about 350,000 square miles, of which over 300,000 are in the United States, exclu- sive of lignite. About 2000 square miles of this entire area contain anthracite, of which half is in the United States, in- cluding the somewhat doubtful New England coal fields. The entire coal production of the world in 1871 was between 225 and 250 million tons, of which England produced 110 millions and the United States 41 millions. About 20 millions of the entire amount was anthracite, of which 15 million tons were produced in Pennsylvania, and the remainder in South Wales, France and other countries. The first authentic account which we find of the use of an- thracite in the United States was in 1768-69, when it was used by two blacksmiths from Connecticut, named Gore. It did not, on account of the difficulty of making it burn, come into use for domestic purposes till 1808, when Judge Fell succeeded in burning " stone coal" in a grate of his own construction. This was probably the first successful use of anthracite for general purposes in the world. So imperfectly were the properties of this fuel understood, and so little known of its proper manage- ment, that four years later, Col. Shoemaker, who had disposed 30 MECHANICAL DENTISTRY. of several loads of it to parties in Philadelphia who were unable to burn it, was arrested, upon a writ obtained from the city authorities, as an impostor and swindler, who had sold them rocks for coal. Prof. H. D. Rogers explains the formation of anthracite by supposing it to be the result of altered bituminous coal meta- morphosed by intense heat, and, of course, by heat induced subsequent to the formation of the bituminous beds; and he further explains the escape of the volatile portion of the latter as gas through cracks and openings caused by the plication of the anthracite strata. This plication follows closely the general type of the palaeozoic rocks, which are intensely crushed and folded near the contact of their edges with the igneous or gran- itic rocks, and much less plicated and distorted in a western direction. This theory, though natural and ingenious, is con- troverted by others who contend that anthracite is not a meta- morphosis of bituminous coal, but as much a normal creation as the bituminous variety itself, from a combination of its con- stituents under superior heat, however the original elements were produced. The particular mineral fuel under consideration has been treated of here somewhat at length, for the reason that it is being more generally employed of late years by the dentist, not only for refining and general heating purposes, but more especially in those important processes of the dental laboratory in which more or less refractory silicious substances requiring a high, uniform and prolonged heat, are employed in com- pounding body and gum enamels, in baking mineral teeth, and in the construction of continuous-gum work. For the latter especially, it is preferred by many to coke, in connection with solid fuel furnaces. Owing to the difficulty of igniting anthracite, it is custom- ary to mix with it at first about an equal quantity of charcoal. Its proper combustion after ignition, when burned alone, re- quires a strong draught, which is ordinarily attainable in'use of the ordinary draught or muffle furnace properly connected with a suitable flue. Under conditions that insure more or less complete combustion, the chief of which is a generous FUELS. 31 supply of oxygen, anthracite will yield a higher temperature than any other kind of solid fuel. The blast furnace is, there- fore, best adapted to this end, though for all ordinary purposes requiring heat in the dental laboratory, the ordinary chimney draught will be sufficient.' To recapitulate somewhat, it may be said, not only in reference to anthracite, but to the other solid fuels mentioned, that in order that the greatest amount of heat may be generated, it is necessary that the conditions essential to their most perfect combustion should be strictly observed; these, as before stated, have reference mainly to an unob- structed circulation of air, in order that oxygen may be freely supplied to them. To this end the furnace should be kept clean, the bars of the grate unbroken, and a good draught obtained. The condition in which the fuel is applied will also modify the results. Thus, for example, if the lumps are too large, they will absorb heat, and caloric will be lost; if too small, they will be too rapidly consumed. It is essential, also, to have the fuel as free as possible from dust and dirt, as these fine particles in any considerable quantities obstruct the draught, and prevent a thorough ignition of the mass. Coke, especially, should be preserved clean, and should be broken into fragments not larger than an inch or an inch and a half in diameter, and, as nearly as possible, in the form of blocks or cubes, as these leave more open spaces for the free circulation of air. GASEOUS FUEL. Illuminating Gas.—The ordinary illuminating gas, derived from the destructive distillation of bituminous coals, is a form of fuel that, of late years, is rapidly supplanting the use of the liquid and solid varieties for heating purposes in the dental laboratory. Within a comparatively short time, the introduc- tion of gas, for the uses indicated, marks an era in prosthetic practice, so far as the application of heat for metallurgic pur- poses is concerned, in which inventive genius has been indus- triously and successfully employed in devising and perfecting appliances designed to obviate entirely the necessity of employ- ing other forms of fuel heretofore used, and which are, in many respects, inconvenient and objectionable. So fruitful have been 32 MECHANICAL DENTISTRY. these later devices in meeting the necessities of the dental met- allurgist, and so reasonably certain is it that more extended experiments in the construction of furnaces adapted to this mode of producing heat will, in the near future, meet all the requirements of ceramic art, as applied to dental prosthetics, that it may be confidently predicted that all solid fuels for these purposes will be wholly banished from the laboratory wherever gas can be commanded for the generation of heat. The latter, intermixed with atmospheric air in proper proportions, and used in connection with burners and furnaces of suitable con- struction, is, in all essential respects, preferable, since it is com- paratively free from dirt and smoke, and is capable of producing a rapid, equable and intense heat, which is completely under the control of the operator as respects duration and the degree of temperature required for any given operation. Natural gas has, until recently, been obtained only in very limited quantities. There are many localities where combus- tible gases have long been known to issue from the earth. Gas has been used in China for centuries, conveyed in bamboo tubes from fissures in salt mines, in excavations from 1200 to 1600 feet in depth. Near the Caspian Sea, in Asia, there are several so-called eternal fires caused by gas issuing from the soil. In parts of New York it issues from bituminous limestone inter- spersed among the slates and sandstones of the Portage group; but the most prolific sources of natural gas are in the coal regions of western Pennsylvania, where rapidly multiplying wells are yielding almost unlimited supplies of this light and heat-producing combustible, and which, in some of the larger cities, is being utilized not only for illuminating purposes, but for fuel in many of the manufacturing establishments. The chief supplies of illuminating gas, however, are derived from the destructive distillation of various grades of bituminous coal, and, to a more limited extent, from wood, peat, resin, pe- troleum, oils and fats, and from water and coke. As the gas used in the dental laboratory for the generation of heat is the common house illuminating gas, obtained from coal, this variety only will be treated of in this place. Bituminous coals, such as English cannel and boghead coals, FUELS. 33 Ohio cannel, and the coking coals of Pennsylvania, Maryland and Virginia, are commonly used in the manufacture of illumi- nating gas. When bituminous coal is heated to redness in the presence of air, it is principally converted into gases which unite with oxygen; but if air is excluded, as when the coal is confined in retorts, the gaseous products, unable to unite with oxygen, may be collected in receivers and burned in tubes. The products of the destructive distillation of bituminous coal consist of a great number of gases, liquids and solids, which may be conveniently included under the following heads, ac- cording to an analysis by Bunsen:— Coke...........68.93 Olefiant Gas......... 0.78 Tar.............12.23 Sulphuretted Hydrogen. ... 0.75 Water............ 7.40 Hydrogen.......... 0.50 Marsh Gas.......... 7.04 Ammonia.......... 0.17 Carbonic Oxide........ 1.13 Nitrogen.......... 0.03 Carbonic Acid........ 1.07 The illuminating power of the gas may be regarded as depending principally upon the amount of olefiant gas (heavy carburetted hydrogen) which it contains, the bulk of other gases being carriers rather than light producers. The olefiant gas is separated by ignition into marsh gas (light carburetted hydrogen) and carbon, the solid particles of which become incandescent and emit white light, which is observed in the luminous cone of a gas flame, and which has the same consti- tution as that of a candle. The luminosity of a gas flame depends both upon the percentage of heavy hydrocarbons it contains, and the amount of atmospheric air or oxygen mixed with it. With the admixture of air or oxygen, the illuminating power of the gas is diminished, while there is at the same time increased evolution of heat. This fact is of interest and value to the dentist, since it underlies the construction of all the modern forms of heating appliances made on the principle of the Bunsen burner, which provides for intermingling currents of atmospheric air and gas. Oxygen thus supplied to the gas jet, and combining with the carbon at the moment of ignition. greatly augments the heat of the flame, while the latter becomes almost non-luminous. 3 CHAPTER II. APPLIANCES USED IN THE GENERATION AND APPLICATION OF HEAT. The modes of generating heat, and the appliances used in its application to the various mechanical processes of the dental laboratory, will require more or less detailed descriptions of the several agencies employed for these purposes. These relate to Lamps, Burners, Blowpipes, Supports, Crucibles, and Furnaces. As full a description of these several appliances will be given as is compatible with the scope of the present work. The agencies employed in the generation and application of heat alluded to under the head of lamps, burners, supports and blowpipes, are such as are used chiefly in soldering, one of the most important, and not always the least difficult, processes of the dental laboratory, while furnaces are largely used for melt- ing and refining purposes, compounding body and gum ma- terials, baking porcelain teeth, and in constructing continuous- gum work. Heaters are adapted to a variety of purposes requiring moderate temperatures, as melting some of the more fusible metals, warming water, heating plaster molds prepara- tory to packing plastic substances, etc. LAMPS. Oil Lamp.—When common lamp or lard oil is burned, the form of lamp represented in Fig. 1, may be used. It is well Fig. l. adapted to the necessities of dentists who are unable to com- mand gas in blowpipe manipu- lations. It should hold from one to two pints, and should have a spout one inch or more in di- ameter where it joins the body of the lamp, tapering gradually to three-fourths of an inch at the top. The spout should be GENERATION AND APPLICATION OF HEAT. 35 well filled with wick, but not so tightly as to prevent it from being freely saturated. The wick should be kept well cleaned and trimmed, and fresh oil should be substituted whenever that in use becomes thickened by dirt or otherwise deteriorated. A somewhat novel form of oil lamp, the same combustible Fig. 2. WICK HOLDER TURNED HaLEJLREVOLUTION. fuel just alluded to being used, is shown in Fig. 2. The wick holder is of unique design, being adjustable to any desired angle by simply revolving it in the fixed collar. The wick holder lifts out for refilling. When kerosene oil is used as a fuel in the production of heat Fig. 3. for soldering purposes, a different form of lamp should be used. In the use of either of those last described, there is danger of explosion should the flame, mixed with air, communicate with the kerosene in the body of the lamp. The same danger accompanies the use of alcohol, and the same precautions are 36 MECHANICAL DENTISTRY. Fig. 4. necessary in the management of both these fuels. For a more particular account of their proper- ties and the conditions under which they may be safely em- ployed in connection with solder- ing lamps, the reader is referred to the chapter on Fuels. In the use of pure kerosene or alcohol, a lamp like the one shown in Fig. 3 may be safely used. The centre of the upright portion of the spout is traversed by a small tube extending throughout, and open at both ends, to admit of the application of a jet of air to the lower orifice, impelling the flame from the centre and thereby intensifying the heat. Around this central tube the wick is Fig. 5. arranged, the space occupied by the latter communicating with the body of the lamp through the horizontal arm of the spout. A lamp closely resembling the one just described is the Franklin Safety Lamp, represented in Fig. 4. It consists of a reservoir five inches in diameter by two and a half inches deep. The wick holder, three inches long by two and a half inches in diameter, is connected with the reservoir by a curved tube five inches long by three-sixteenths of an inch in diameter. Figs. 5 and 6 represent safety soldering lamps designed more especially for alcohol, and are somewhat analogous in construc- tion to the last two described. In Fig. 6 the lamp is suspended GENERATION AND APPLICATION OF HEAT. 37 on pins between two uprights, the burner being retained in the desired position by a spring attached to the tube and rest- ing on the base or pan. Fig. 5 is provided with an additional wick tube, which makes it useful for general laboratory work as well as for soldering. Fig. 6. BURNERS. For all the minor operations of the laboratory requiring the application of moderate degrees of heat in the use of either the mouth or the simpler forms of bellows blowpipe, the fore- going lamps will be found serviceable and efficient. When, however, gas can be commanded, it is preferable to the oils or alcohol for heat-producing purposes, on account of its greater convenience and freedom from accident. The ordinary gas flame is unsuitable for soldering or other operations, by reason of the carbonaceous residue with which it is constantly charged. This source of uncleanliness may be gotten rid of by an admixture of air with the gas flame. This intermingling of gas and air currents for the purpose of augmenting the heat of the gas flame, and of rendering it in other respects more suitable for general metallurgic purposes, was first practiced by Bunsen, a distinguished German chemist, by means of a simple contrivance repre- sented in Fig. 7. All modern heat-pro- 38 MECHANICAL DENTISTRY. ducing appliances usually denominated Bunsen burners utilize the same principle in the generation of heat, and differ only in mechanical construction from Bunsen's original device. A very simple contrivance embracing the principle of the Bunsen burner, is shown in Fig. 8. A represents an ordinary gas burner attached to a circular cast-iron base, with a station- ary tube, C, entering near the bottom, for the supply of gas. B is a hollow cylinder of sheet brass or copper, the lower half of which is perforated with small holes for the admission of air. This is placed on the burner, the perforated end fitting over the central portion, leaving something of a space above, between Fig. 8. the burner and cylinder, for the free circulation of air. The cylinder, when in place, should extend two inches or more above the tip of the burner. The gas is supplied through a flexible rubber tube connected with the stem of the burner, and connected at the other end with any ordinary gas burner conveniently located in the laboratory. For soldering small pieces, and for many other purposes requiring a ready and manageable heat, the author has used this simple appliance, with great satisfaction, for many years. To obtain a flame of greater volume than is possible with GENERATION AND APPLICATION OF HEAT. 39 the gas burner just described, a Bunsen burner may be con- structed in the manner described by Prof. Essig in his valuable work on Dental Metallurgy. Fig. 10. This consists in attaching to the base of an ordinary Bunsen burner (Fig. 9), such as is sold at the dental depots, a piece of Fig. 11. brass tubing six inches in length by one and a quarter inches in diameter. Over the top of this, in order to properly spread the flame, a piece of fine wire gauze is fastened, by means of a 40 MECHANICAL DENTISTRY. ring of sheet brass one quarter of an inch in width. Gas is supplied in the same manner described in connection with Fig. 8. This contrivance, while it fully meets the general requirements of the operator, is especially adapted to the pro- cess of soldering entire dentures, and for melting alloys of gold and silver in considerable quantities. A compact and convenient burner for general laboratory uses is represented in Fig. 10. It is especially useful in " waxing up" a base plate, heating water, vulcanizing, and other minor operations requiring a moderate and easily-graduated heat. Another heating apparatus of recent introduction, designed, in part, for soldering with the use of blowpipes, is represented in Fig. 11. It is called the "Duplex Burner," and will be found very convenient for laboratory use. In addition to the usual Bunsen burner, a large flame for the blowpipe can be had by rotating the upper portion upon the base. A small jet, when once lighted, ignites either flame, so that it is always ready for use. There are many other varieties of these heating appliances constructed on the principle of the Bunsen burner, but it is not deemed essential to further multiply them in this place. BLOWPIPES. Following the descriptions of lamps and burners given in the preceding pages, it would seem appropriate to consider next the various forms of blowpipes used in the application of the heat produced by means of the appliances named. Various modifications in the form of the blowpipe have been introduced from time to time, and are named according to the means used to produce the blast, as—mouth, bellows, self-acting or spirit, and hydrostatic blowpipe. In addition to the varieties mentioned, there are others, used in producing extreme degrees of heat, as the " oxygen blow- pipe," with which the flame is blown with a jet of oxygen; and another, with which the two gases, oxygen and hydrogen, are burned, called the " oxy hydrogen blowpipe." The latter is capable of producing a heat that immediately fuses the most refractory substances, as quartz, flint, rock-crystal, plumbago, etc. With GENERATION AND APPLICATION OF HEAT. 41 it gold is volatilized, and iron rapidly consumed when placed in the flame; while platinum, next to iridium the most infus- ible of all known metals, has been melted in quantities exceed- ing one hundred ounces by means of this powerful instrument. As, however, these blowrpipes are of no special practical utility in the dental laboratory, any further reference to them will be omitted. Nor is it deemed necessary to embrace descriptions of spirit blowpipes, as they have fallen, of late years, almost wholly into disuse. MOUTH BLOWPIPE. This instrument has been long in use, is simple in its form and construction, and, for general use in the application of moderate degrees of heat, is both convenient and economical. Those accustomed to its use are enabled to produce a continu- ous blast of considerable force, and soon acquire the facility of regulating the heat produced with equal if not greater pre- cision than can be readily attained in any other way. Fig. 12. The most simple form of the mouth blowpipe is shown in Fig. 12. It consists, usually, of a plain tube of brass, larger at the end applied to the mouth, and tapering gradually to a point at its other extremity, the latter being curved and tipped at the point with a conical-shaped, raised margin, to protect it from the action of the flame; the calibre of the instrument termi- nates here in a very small orifice. The point of the instru- ment, as well as that part of it received into the mouth, is sometimes plated with a less oxidizable metal than brass, as silver or platinum. The stem is generally from twelve to twenty inches in length, and the mouth extremity from one- half to three-fourths of an inch in diameter. In operations requiring protracted blowing, a somewhat dif- ferent form of the instrument will be required, owing to the accumulation of moisture within the tube, which, being forci- 42 MECHANICAL DENTISTRY. bly expelled from the orifice, spurts upon whatever is being heated and interrupts the blast; also, on account of the fatigue, which in process of time renders the muscles of the mouth and face engaged in the act to a great extent powerless. The difficulties mentioned may be obviated, in a great meas- ure, by applying the form of blowpipe represented in Fig. 13. To the mouth extremity is attached a circular concave flange or collar which receives and supports the lips. To the shaft, near its curved extremity, is adjusted either a spherical or cylindrical chamber which collects and retains the moisture as it forms within the pipe. By allowing that part of the tube connected with the curved end to pass part way into the cham- ber, a basin is formed at the depending portion of the latter, which, by collecting the fluids, will effectually prevent them from overflowing and passing into the tube beyond. Fig. 13. Thomas Fletcher, of Warrington, England, has introduced modifications in the construction of mouth blowpipes which are unquestionably improvements upon the simpler forms just described.* One form, styled the hot-blast mouth blowpipe, is shown in Fig. 14. The improvement in this instance con- sists in coiling the air-tube into a light spiral over the point of the jet. This coil takes up the heat which would otherwise be wasted, and utilizes it by heating the air in its passage. It is claimed that with the use of this instrument much higher tem- * The several appliances embraced in the above chapter, and designated by the Figures 2, 14,15,16,17,18,19, 22, 24, 25, 26, 27, 42, 44, 45, 48, 49, 50, 51, are such portions of Fletcher's heating apparatus as are more especially adapted to the work of the dental laboratory, and are believed to possess peculiar and unequaled ad- vantages in the application of heat for dental purposes. For the illustrative cuts above alluded to, the author is indebted to the Buffalo Dental Manufacturing Company, sole manufacturers of Fletcher's heating apparatus in this country. ° GENERATION AND APPLICATION OF HEAT. 43 peratures are reached than is possible with the ordinary blow- pipe, and that with the same amount of blowing nearly double the work is accomplished, while, if a high heat is not required, the labor of blowing is reduced in proportion. A similar form of instrument (Fig. 15) is made with a hard-rubber mouth- piece. Fig. 14. Another form of mouth blowpipe by the same inventor is exhibited in Fig. 16. It will be seen to be wholly unlike any mouth blowpipe yet devised, and admits of great latitude of movements in the application of heat. The form of the mouth- Fig. 15. piece is especially adapted to continued blowing without strain on the lips, while the opening is well under the control of the tongue. The blowpipe proper is held as a pencil, the chamber collecting condensed moisture and preventing the passage of Fig. 16. heat up to the end. The instrument can be readily changed from a cold to a hot-blast blowpipe by substituting the coil (b) for the plain jet or tip. There are other allied forms of the mouth blowpipe, but as they are constructed more especially for chemical examinations or analyses, and as they possess no advantages, for dental 44 MECHANICAL DENTISTRY. purposes, over those already mentioned, a description of them is not deemed necessary. Mechanism Involved in the Act of Producing a Continuous Blast with the Mouth Blowpipe.—As a steady, continuous current of air from the blowpipe is preferable to the interrupted jet, in all those operations where it is desired to produce a steadily augmenting heat, the following remarks explanatory of the method of producing it are subjoined, in the belief that they will render easier a process not always readily acquired. " The tongue must be applied to the roof of the mouth, so as to interrupt the communication between the passage of the nostrils and the mouth. The operator now fills his mouth with air, which is to be passed through the pipe by compressing the muscles of the cheeks, while he breathes through the nos- trils, and uses the palate as a valve. When the mouth becomes nearly empty, it is replenished by the lungs in an instant, while the tongue is momentarily withdrawn from the roof of the mouth. The stream of air can be continued for a long time without the least fatigue or injury to the lungs. The easier way for the student to accustom himself to the use of the blow- pipe, is first to learn to fill the mouth with air, and while the lips are kept firmly closed to breathe freely through the nos- trils. Having effected this much, he may introduce the mouth- piece of the blowpipe between his lips. By inflating the cheeks, and breathing through the nostrils, he will soon learn to use the instrument without the least fatigue. The air is forced through the tube, against the flame, by the action of the muscles of the cheeks, while he continues to breathe without interruption, through the nostrils. Having become acquainted with this process, it only requires some practice to produce a steady jet of flame. A defect in the nature of the combustible used, as bad oil, such as fish oil, or oil thickened by long stand- ing or by dirt, dirty cotton wick, or an untrimmed one, or a dirty wick holder, or a want of steadiness of the hand that holds the blowpipe, will prevent a steady jet of flame. But, frequently, the fault lies in the orifice of the jet, as too small a hole, or its partial stoppage by dirt, which will prevent a steady jet of air, and lead to difficulty. With a good blowpipe, the GENERATION AND APPLICATION OF HEAT. 45 air projects the entire flame, forming a horizontal, blue cone of flame, which converges to a point at about an inch from the wick, with a larger, longer, and more luminous flame envelop- ing it, and terminating at a point beyond that of the blue flame."* BELLOWS BLOWPIPE. There are many processes of the dental laboratory requiring the application of a higher temperature than is obtainable with the mouth blowpipe. A more powerful and persistent air blast is readily produced by a bellows or foot blower, used commonly in connection with a burner of suitable form attached to the common gas jet, by means of which the gas is furnished with Fro. 17. the oxygen required for its combustion in a state of intimate mixture. A simple and compact form of bellows or foot blower is shown in Fig. 17. The pressure obtainable with this instru- ment is continuous, equable, and completely under the control of the operator, but the current may be greatly increased in power after the rubber disc is distended until forced against the net. A bellows of similar construction, but with the position of the blower reversed, is shown in Fig. 18. By this arrangement the disc is less liable to injury,-while it prevents the valve from picking up dirt from the floor. Fig. 19 represents still another modification, in which the bellows and reservoir are separated, * The Practical Use of the Blowpipe.—Anon. 46 MECHANICAL DENTISTRY. the latter being suspended in some convenient place out of the way of mechanical injury. A contrivance essentially different in its construction from the ordinary bellows employed to produce the air jet is shown in Fig. 20, and is known as the " Burgess Mechanical Blow- pipe." When in use, the air is drawn into a cylinder and con- densed in an air chamber, ready to be used in large or small quantities at the will of the operator, by a rapid or slow move- ment of the treadle. When operating, place the entire foot upon the treadle, so that an easy rocking motion is obtained; by Fig. 19. _________ tl_________ pressing the toe downward, air is drawn into the cylinder, and in reversing the motion it is driven into the air chamber above. The pipe outlet is much smaller than in the mouth blowpipe, to enable a pressure to be obtained, which is increased or diminished by a quick or slow motion of the treadle. The air chamber is easily filled, and when so a constant supply of pure air is at the control of the operator. The blowpipes used in connection with the bellows are of various forms. Fig. 21 represents one form of apparatus em- ployed in the application of the air blast to the gas flame. GENERATION AND APPLICATION OF HEAT. 47 A movable gas jet attached to two short arms of an ordinary gas pipe is made to receive within it the blowrpipe point con- nected with the rubber tube, the air tube terminating a little within the open mouth of the gas jet; it is thus a tube within a tube, with a space between them for the admission and passage of gas. The gas, being admitted by turning the tap connected with the gas pipe, is ignited, when the current of air from the bellowrs will strike the centre of the flame and pro- ject it upon whatever is to be heated. The connected portions of the air and gas jets are so attached to the main pipe as to Fig. 20. admit of an upward and downward motion, while the volume of gas and air is readily graduated by the stop-cocks attached to the air and gas tubes. A bellows blowpipe, constructed on similar principles, but admitting of greater latitude of movements, is exhibited in Fig. 22. As will be readily observed, it is capable of being adjusted in any desired position. The jet tube may be raised or lowered to any height, and turned in any direction. A 48 MECHANICAL DENTISTRY. touch will direct the flame on any point while the blowpipe stands in the same position on the table; there being no necessity for raising, lowering, or adjusting work before it. Macomber's gas blowpipe, Fig. 23, differs somewhat in con- struction from the latter, its capability of adjustment being regulated by a ball and socket attachment which imparts to it, at the will of the operator, a latitude of movement or adjust- Fig. 23. ment of the blowpipe point that is practically without limit. The direction of the point, 1, is regulated by the joint 3, and the supply of gas controlled by the stop-cock, 2. The air is A very convenient, manageable, and effective instrument, for many purposes requiring the application of heat in the dental laboratory, is the hand blowpipe shown in Fig. 24. It is capable of producing very high degrees of heat, but the intensity of the latter may be graduated at the will of the operator, as the stop-cocks, which are both under perfect control of the thumb of the hand which holds the blowpipe, GENERATION AND APPLICATION OF HEAT. 49 regulate the supply of gas, and control the volume of air. The air jet is one-eighth inch bore, and requires a supply from a bellows. Two very convenient forms of the Fletcher automatic blow- pipe are shown in Figs. 25 and 26. The latter, which is Fig. 25. Fig. 26. Fig. 27. mounted on a ball joint, is adjustable at the will of the operator. In cases requiring a heat of sufficient intensity to readily fuse pure gold, as in the construction of continuous-gum work, where this metal in its unalloyed form is used to unite the teeth and plate, the hot-blast blow- pipe contrived by Mr. Fletcher, ex- hibited in Fig. 27, will be found efficient for the purpose. The air pipe, as will be seen, is coiled around the gas pipe, and both are heated by three small Bunsen burners, the gas supply to which is regulated by a separate stop-cock, as shown in the figure. The air blast is obtained with the bellows or foot blower connected with the blowpipe by means of a flexible rubber tube. It is claimed that the heat-producing power 5527165752 50 MECHANICAL DENTISTRY. of this simple device is but little inferior to that of the oxyhydrogen blowpipe, and may be useful, therefore, in the treatment or management of highly refractory metals or substances not readily acted upon by the highest heat of the ordinary forms of bellows blowpipe. The several forms of bellows blowpipe illustrated in these pages are complete and efficient, and admirably adapted to the necessities of the mechanical operator. In most instances, the jet may be elevated or depressed at will, while the force of the air current and the volume of gas flame can as readily be in- creased or diminished. The operator is thus enabled, with the greatest ease, to produce a heat adapted to the most delicate operations, or to instantly change it to a heat so intense that pure gold in considerable quantities is almost immediately fused in the flame. They are, therefore, well adapted to all operations in the laboratory, but will be found of special utility in the construction of work requiring pure gold as a solder. Fig. 28. HYDROSTATIC BLOWPIPE. Whenever pressure can be obtained from the flow of water from public waterworks, the form of hydrostatic blowpipe shown in Fig. 28 may be used to ad- vantage in the production of an air blast of sufficient force and duration for all ordinary soldering purposes. The blast produced is equable, and its force may be regulated somewhat either by increasing or diminishing the flow of water into the cylinder from the supply pipe, or by pressure with the fingers upon the flexible tube connected with the blowpipe point. It is so sim- ple and economical in its construction that any dentist may, with little trouble and at a trifling cost, provide one for his laboratory. To the centre of the top of the cylinder is adjusted a stop- cock, to freely admit air when the water GENERATION AND APPLICATION OF HEAT. 51 is being discharged through the faucet at the bottom. To the top, on one side, a rubber tube is attached, connecting at the other end with a blowpipe point. The water being admitted to the tank through the supply pipe near the bottom, the con- tained air is compressed, and forcibly expelled through the rubber tube upon the flame. When the cylinder becomes filled, or .partially so, the faucet on top should be opened, and the water drawn off through the discharging pipe. A small glass tube, communicating with the interior of the cylinder on one side near the bottom, extending up the side, and again entering the cylinder at the top, will always indicate the depth of water in the tank. Those unable to command the facilities afforded by water power may avail themselves of the following contrivance, which combines, mainly, all the advantages of the blowpipe just de- scribed. A cylinder of the form mentioned, but with an open top, is nearly filled with water, and another, similarly formed but inverted, or with its closed end above, is made to fit and slide into the first. To keep the second cylinder steadily in an upright position, it may be supported laterally by strips of iron riveted to the outside cylinder and extending some distance above the top of the latter. Weights are placed on top of the inverted tank, when the contained air will be forcibly com- pressed and forced, as in the other case, through an air tube attached to its upper closed extremity. When the air is ex- pelled, the upper cylinder may be raised out of the water more readily and quickly by opening a stop-cock attached to the upper end, the air being thus more freely admitted than through the blowpipe point when the tank is raised. SUPPORTS. There are many processes in the dental laboratory for which it is necessary to provide a suitable holder or support, as in melting small quantities of gold and silver, and in all the varied operations requiring the use of solder. For melting, and soldering small pieces, a variety of simple devices, easily and economically constructed, may be used, among which are the following:— 52 MECHANICAL DENTISTRY. Charcoal, either alone or combined with other non-conduct- ing substances, is very commonly employed, and being com- bustible, adds materially to the heat of the blowpipe flame. A convenient support of this kind may be made by selecting a fair-sized block of compact, close-grained charcoal, derived from some of the hard woods, such as oak or beech, and investing it in plaster one-half or three-fourths of an inch thick, one end or side being left open and made concave, to receive whatever is being heated. Or a plaster cup, two or three inches deep and three or four inches in diameter, may be used, its in- terior being filled with a mixture of plaster, sand, asbestos, and pulverized charcoal. Coke, encased in the same manner as charcoal, may be substituted for the latter, and has the merit of being more lasting, but in all other respects is inferior for the pur- pose. Supports for the uses under consideration are also some- times made of pumice-stone. Prof. Essig * says: " Platner's ' Manual of Qualitative and Quantitative Analysis with the Blowpipe,' page 15, gives a method of artificially preparing good solid supports of charcoal which might be found of value in the dental laboratory. It consists of mixing charcoal dust (which must not be too finely ground) with starch paste. The latter is prepared by combin- ing one part of starch with six parts of boiling water. These are stirred in an earthen pot" until all the meal is converted into paste. This paste is rubbed in a porcelain mortar, with fre- quent additions of charcoal dust, until the mass becomes too tough for further admixture, when enough of the coal dust is kneaded in by the hands to render the whole mass stiff and plastic. From this the desired forms of blowpipe coals can be made, allowed to dry gradually and thoroughly, and then heated to redness in a covered vessel, so as to char the starch paste. The charring may be regarded as complete when the evolution of gases from the mass ceases, or when it has been heated to a dull redness. Coals thus formed are of the proper firmness, and ring like ordinary good charcoal when thrown on the table." Manufactured supports composed of asbestos and carbon, very * Dental Metallurgy. GENERATION AND APPLICATION OF HEAT. Do convenient and durable, may be obtained at the dental depots. Fig. 29 represents a carbon block designed for melting and sol- dering, and Fig. 30 a carbon cylinder used chiefly for soldering small pieces. Fig. 29. Fig. 30. For soldering purposes exclusively, especially in uniting teeth to a metallic base, either of the following means of support for the invested piece will be suitable: A simple holder, which the operator himself.can easily construct, may be made of a circu- Fig. 31. lar or semi-elliptical piece of heavy sheet iron, the margin of which is serrated and turned at right angles, forming a cup. To the under side and centre of this an iron rod, ten or twelve inches long, may be permanently riveted, or it may be made to 54 MECHANICAL DENTISTRY. revolve on the handle, so that the heat may be thrown directly upon any particular part of the piece to be soldered without disturbing the latter. A small hand furnace (Fig. 31) is sometimes used, and will be found a very convenient and useful apparatus, not only for soldering, but for preparatory heating. It consists of a funnel- shaped receptacle made of sheet iron, with a light grate or perforated plate of the same material adjusted near the bottom, and an opening on one side, underneath the grate, for the admission of air. The upper part of the holder is surmounted by a cone-shaped top, which may be readily removed by a handle attached to it, while to the bottom of the furnace is attached an iron rod, five or six inches long and terminating in a wooden handle. The piece to be soldered is to be placed inside on a bed of charcoal, the top adjusted to its place, and the fuel ignited; when the case is sufficiently heated, the top may be lifted off, and the piece remaining in the furnace soldered with the blowpipe in the usual manner, the furnace thus serving the purpose of a holder. CRUCIBLES. Crucibles are small conical-shaped vessels used by the dentist principally for the purposes of melting and refining metals used for plates, compounding metallic alloys, preparing and compounding the various ingredients employed in the manu- facture of porcelain teeth and continuous-gum work, etc. They combine in a high degree the properties of infusibility, exemp- tion from the attack of substances fused in them, the power of resisting sudden alternations of temperature, and impermea- bility to fluids and gases. The Hessian crucibles, which are in most common use among dentists, are composed of silica, alumina and oxide of iron. Plumbago crucibles are also made from special patterns, and expressly designed for Fletcher's furnaces. For a more particular description of the various components entering into the structure of crucibles, as well as the manner of manufacturing them, the reader is referred to Piggot's Dental Chemistry and Metallurgy, and other works treating more fully of the subject. GENERATION AND APPLICATION OF HEAT. 55 • FURNACES. It would be inconsistent with the design of the present work to introduce a description of any forms of furnace other than those of practical use to the dentist. Many of those used in the arts, or for chemical and pharmaceutical purposes, embrace almost endless varieties, and have no special adaptation to the uses required of them in the dental laboratory. Draught or Wind Furnace.—A very convenient, portable and economical furnace may be made of sheet iron, of any desired Fig. 32. shape or dimensions, though usually of small size and cylin- drical in form. A light grate, or heavy piece of sheet iron, perforated with holes, to admit of the passage of air, should be adjusted near the bottom, while above and below the grate are two openings, the lower one communicating with the ash pit, and the upper one for the introduction of fuel and substances to be heated. By surmounting this simple apparatus with a pipe, or connecting it with the flue of a chimney, it will be 56 MECHANICAL DENTISTRY. found efficient in many of the minor operations of the shop, as melting metals, heating pieces preparatory to soldering, annealing, etc. A more durable and serviceable draught furnace, however, may be built of masonry, a convenient form of which is repre- sented in Fig. 32. The construction of this stationary fixture is so plainly exhibited in the cut that any extended description of it is deemed unnecessary. The upper holes represent the entrance to the fire chambers, which are distinct from each Fig. 33. other; the lower ones communicate with the ash pit, which is common to both chambers. Two fire apartments are here shown, one for melting and refining the more precious metals, heating up operations for soldering, etc., the other being used exclusively for fusing the baser metals, as zinc, antimony, lead, etc. These furnaces are sometimes constructed with a single fire chamber, but the one exhibited is in every way preferable. Baking Furnace.—-The chief purposes to which these, fur- naces are applied are the manufacture of porcelain teeth, single GENERATION AND APPLICATION OF HEAT. 57 and in sectional blocks, the preparation of silicious compounds, and the construction of what is known as " continuous-gum work." One of the most approved forms of this furnace is exhibited in Fig. 33. Fig. 34. The body of the furnace rests upon a cast-iron framework or basement, which serves the purpose of an ash pit. The grate immediately over this inclines from each side of the furnace 58 MECHANICAL DENTISTRY. toward the bottom and the centre of the ash pit, to afford more ample room for fuel directly underneath the lower muffle. The upper portion or body of the furnace is made of fire clay, and contains three muffles arranged horizontally; the upper two, termed " annealing muffles," are designed more especially for drying substances, partial heating preparatory to final baking, and to receive substances from the lower muffle to be gradually cooled. The lower or main muffle is for general baking purposes requiring the employment of extreme degrees of heat. Each muffle is provided with fire-clay slabs or slides, on which substances to be heated are placed and introduced into the muffles; and also plugs of the same material to close the openings to the former. Openings are made on each side of the furnace, intermediate between the muffles, for the intro- duction of fuel, and to afford ready access to the latter with tongs or other implements. These entrances are also provided with plugs, which are applied during the process of heating. This furnace should be connected with a flue having a strong and unobstructed draught. A furnace of somewhat similar construction, devised by Dr. Ambler Tees, is shown in Fig. 34. Dr. Tees, in a communica- tion to the author, says concerning this appliance, which he designates as the " Lilliput" furnace: " Continuous-gum work has heretofore been looked upon as formidable, on account of the necessity of using large furnaces to obtain the requisite degree of heat; but since the introduction of the Lilliput fur- nace, in 1880, and the systematic way of managing it, it has become a pleasure instead of a terror." This little furnace is made of fire clay; it is but 15J inches high, 12 inches wide and 8 inches deep, with walls 1 inch thick; being divided into three sections, it can be handled and managed by a child. Scarcely more than half a peck of coke is necessary for each heat. In the fall, winter and spring, when the draught is at its best, a coat of body can be fused in about thirty-five minutes after the fire is lighted; and in the summer, within fifty minutes. By having the coke properly screened, and the kindling wood dry, and a convenient receptacle for them, the labor of starting the fire is scarcely more than light- GENERATION AND APPLICATION OF HEAT. 59 ing the gas. It is for sale, with all the necessary appurtenances, by dental dealers. A modification of the last named furnaces, more recently introduced, and designed more especially for continuous-gum work, is exhibited in Fig, 35. The fire pit below the muffle is of more than usual capacity, insuring, it is claimed, perfect results at each baking. The part which is subjected to the greatest heat is free from angles and incased with sheet iron, rendering it less liable to crack from long use. The fire or ashes may be with- drawn by removing the two projecting grate bars. It is 24 inches high and 121- inch es in diameter. As the purposes, heretofore stated, for which these several furnaces are designed, require a steady, intense and persistent heat, the fuels commonly used, as fulfill- ing most perfectly these indications, are coke, or a mixture of charcoal and coke, and anthracite, pre- ference being given, by many, to the latter. It will be observed that, in connection with the several kinds of furnaces heretofore mentioned, heat is generated by the use of solid fuels. Within the past few years, baking or muffle furnaces have been constructed with reference to their special adaptability to the use of gas in combination with the air blast. While these later devices commend themselves, on the score of their greater convenience and economy of time in firing, and their freedom from the dirt and smoke attending the use of solid fuels, their successful application to .the special uses for which they are mainly designed has been attended with difficulties which have heretofore been adverse to their general adoption by the profession, and which it has been the aim of inventors to overcome. This has been measurably, if not entirely, accomplished, and the successes so far attained give fair promise of a complete revolution, at no distant day, in the modes of applying heat in all operations concerned in the 60 MECHANICAL DENTISTRY. fabrication of the various forms of dental porcelain. Perhaps the chief obstacle to the successful use of gas in connection with the air blast in the processes relating to the manufacture of porcelain teeth, gum enamels, continuous-gum work, etc, is in the increased liability to so-called " gasing," or the formation of bubbles due to absorption and elimination of gas that finds its way into the muffle during the process of baking. The manner in which this accident occurs is thus accounted for in a communication to the author from Dr. C. H. Land, of Detroit, Mich. Alluding to the kind of furnaces under consideration, the writer says:— " To be able to fuse the body and enamel of which artificial teeth are composed in an easy and convenient manner, is a thing the profession have studiously sought after, realizing that, when properly accomplished, the means to elevate prosthetic dentistry from an ordinary mechanical enterprise to one of true art, would be at hand. The mere construction of a fur- nace after the usual modes has been simple enough, and the question of securing the necessary degree of heat was long ago accomplished. Howrever, the ideal furnace demanded much more. It must possess not only the capacity of a coal or coke fire, but also accomplish the work in less time, and require but the minimum amount of exertion to operate it. Of the many attempts to produce such, nearly all have failed, owing to technicalities that were not well understood. "After many experiments, and their accompanying failures, it has been demonstrated that to heat an eight-inch muffle, three and one-half by two and one-half inches in diameter, to over 2800° F., represents about a one-man power, equivalent to the exertion of running the ordinary foot lathe or the No. 9 bellows, as manufactured by the Buffalo Dental Manufacturing Com- pany, which gives a working pressure of one and one-half pounds to the square inch, and corresponds exactly to the required amount of air pressure and volume necessary to heat an eight-inch muffle to 2800° F. Therefore, to make a furnace larger would require too much power, and one smaller would not do for large pieces of work. In the production of a suitable fur- nace, the whole working apparatus must be as nearly air tight GENERATION AND APPLICATION OF HEAT. 61 as possible, the supply of gas and air must be easily controlled, and well balanced, with the least amount of friction in the passage through the pipes. These, with many minor details, form the basis of a practical gas furnace. CASING THE BODY AND ENAMEL. " The most serious trouble with all gas furnaces has been the extreme liability of injuring the body and enamel by what has been commonly called ' gasing.' The accompanying illustra- tion, Fig. 36, will make the philosophy of combustion more clear, and give the reasons why teeth are injured. A represents the burner, B B B, fire brick lining; C C C, combustion chamber; D, interior of muf- fle. The arrows indicate the direction of the blast. The space in the combustion chamber between the lines E E, is where carbon mon- oxide is formed, a gas containing one equivalent less of oxygen than carbon dioxide, simply an imperfect state of combustion. It is this gas that injures the body and enamel. By refer- ence to the illustration, it will be seen that the little arrows are made to appear passing through the pores of the muffle, and as the direc- tion of the blast from the burner A is directly against the bottom of the muffle, with a pressure of one pound to the square inch, a portion of the carbon monoxide is extremely liable to be forced through its pores, and will be taken up with the body during the first and second biscuiting, here to remain until the enameling process, and as this takes a much higher degree of heat, it causes the gas to be eliminated, as shown in 62 MECHANICAL DENTISTRY. the numerous small bubbles on the surface. The space between the lines E E, and within the combustion chamber C C C, should be known as the first stage of combustion, where a cer- tain portion of carbon monoxide is always present, and the space above the line F, within the chamber C, should be known as the second stage, which is perfect combustion. In the first stage of combustion one equivalent of oxygen from the atmos- phere unites with the hydrocarbon to form carbon monoxide; in the second stage, two, or perhaps three, unite to form carbon dioxide, or carbonic acid. Perfect combustion is always at the extreme point of the blowpipe, as shown in the illustration. "The attempt, therefore, should be to place the muffle as nearly as possible in the centre of perfect combustion. As car- bon monoxide is not consumed short of a temperature of over 2200° F., the teeth should be kept in front of the muffle until it approaches a white heat. Starting from a cold muffle, this will take about twelve minutes, and they should be gradually carried to the extreme end. At a high temperature, there is very little danger of gasing, unless a greater quantity of gas is supplied than the furnace is capable of burning. Having constructed a furnace, and being familiar with many other details that pro- vided a means to overcome all the apparent difficulties, the success of properly baking teeth seemed to be assured, until the muffle began to crack, which usually started in the second or third enameling heat. This let in such a quantity of monoxide of carbon as to ruin the teeth. Here was a difficulty that was overcome by forcing a quantity of superheated air into the muffle, and backing all foul gases out. This proved to be a cure for gasing, but added an excess of oxygen, and it was found that this had a tendency to bleach the gum enamel to a lighter shade. The next step was to inject a pure atmosphere of nitrogen into the muffle, it being a neutral gas, not uniting radically with anything. This was eminently successful, and thoroughly demonstrated the fact that porcelain baked in an atmosphere of nitrogen was absolutely perfect, both in color and texture. It therefore gives me pleasure to be able to an- nounce to the profession, that the baking of all kinds of porce- lain with any of the hydrocarbons has been brought within GENERATION AND APPLICATION OF HEAT. 63 the range of every dental practitioner, so that, with a little ex- perience and knowledge of the above facts, artificial teeth can be baked, with unerring precision, in a very comfortable, cheap and easy manner. By a simple attachment, each furnace pro- duces its own nitrogen as fast as needed, and with recent im- provements in the construction of muffles, and the aid of a small motor, the author has been able to maintain a constant and uniform temperature above 2800° F., by which a slab of sectional gum teeth was completed every seven minutes, at the will of the operator. OLEFIANT GAS AND GASOLINE. " Olefiant gas, with which nearly all our cities and towns are supplied, is a compound of hydrogen and carbon. Its symbols are C2H4, differing from gasoline only in its specific gravity, the composition of the latter being also C2H4. The former will rise to the top of a building, while the latter will fall. The former is more penetrating, therefore more liable to gas the teeth, and hence requires more care in handling. The quality varies in different localities, and sometimes, owdng to the presence of ammonia, it may injure the teeth, or it may be too thin. When properly purified, it should be a rich hydrocarbon. The uncer- tainty of its qualities is frequently the cause of failure. To be successful with gas furnaces, it is absolutely necessary to have a pure and rich hydrocarbon. When the gas pressure is weak or the quality is poor, a gasoline generator may be attached to the pipe, and the current allowed to pass through. This takes up a large percentage of the gasoline, and provides a very rich quality of gas. The eighty-seven per cent, is the best; seventy- four per cent, is too heavy to use without requiring heat to vaporize it. By applying to the Combination Gas Machine Company, a supply can be had. When pure gasoline is used, it is necessary to have a generator so arranged that a portion of the air from the bellows will pass through it. This carries the vapor into the furnace, where it becomes mixed with the proper quantity of air, and will produce as good, if not better, results than any other hydrocarbon. All kinds of crucible and muffle work can be done equally well, also soldering and 64 MECHANICAL DENTISTRY. brazing with the blowpipe. One gallon of gasoline costs fifteen to twenty cents; this will bake one set of teeth. Therefore it will be seen that dentists living in localities where there is no gas will not be deprived of practically the same advantages as their city brethren." Fig. 37. a __ A The following description of a furnace invented by Dr. Land is designed especially to overcome the trouble spoken of above, as well as to provide other advantages :— " Size No. 1, especially adapted for all kinds of muffle work, crucible work, blowpipe work, forging and brazing, assaying, GENERATION AND APPLICATION OF HEAT. ()D and small castings of iron, brass and steel. A muffle 8 inches long, 3£ inches wide, 2| inches high, inside measurement, can be heated to over 3240° F. in 25 minutes, sufficient to melt wrought iron. Fig. 37 represents the furnace closed and ready for muffle work. A A is iron pipe, capable of both a sliding Fig. 38. and swinging motion (see L, Fig. 38), to which the door or plug is securely attached. There is a small hole in the door, covered with a piece of mica, through which all operations can be seen. ()1 >serve that the iron pipe is connected to rubber tubing, B, and with pipe having an air cock, C, which regulates the quan- 5 66 MECHANICAL DENTISTRY. tity of air passing into the mouth of the muffle. It will also be noticed that the pipe passes over the two holes, D D; thus by the escaping flame the pipe is heated to redness and provides a superheated air before reaching the muffle; this column of air forced into the muffle keeps up a counter pressure within, so much greater than the pressure produced by the blast within the fire chamber that all foul gases are prevented from enter- ing the muffle even though it is cracked; thus the most delicate porcelain can be baked without the least danger of so-called gasing. Also, it will be seen that by connecting the rubber pipe with retorts or gasometers any desired vapor or gas could be forced into the •muffle, making the furnace invaluable for scientific experiments. " Fig. 38 illustrates the furnace thrown open, being swung on hinges at the back, exposing the muffle, E. The groove, P P, is packed with asbestos fibre, so that when the sections are brought together the furnace will be perfectly air and gas tight. The hooks, F F, are to hold the upper section secure to the lower. The gas and air connections are so arranged that the ordinary blowpipe can be attached, as shown at G. When the muffle, E, is removed, it exposes two burners and a fire-brick surface made to fit the various appliances for crucible, ladle and blowpipe work. One or both burners can be operated in con- junction with the blowpipe, G. The air cock, R, is to provide a means for shutting off the air supply from either burner when required. H is the gas supply, K, air pipe connecting with the bellows. Size of muffle, inside measurement, 8 inches long, 3| inches wide, 2| inches high. With gasoline gas porce- lain teeth can be enameled in from 10 to 15 minutes; with ordi- nary city gas in from 15 to 25 minutes, according to quality. In 30 minutes a heat sufficient to destroy the muffle can be produced, which indicates a temperature of over 3240° F., much higher than is ever needed for any kind of work, except the fusing of platinum, f inch gas pipe will supply sufficient gas and can be worked with ordinary foot bellows." A gas muffle furnace, with hot-air blast attachment, invented by Dr. William Herbert Rollins, of Boston, Mass., is exhibited in Figs. 39 and 40. This furnace, designed especially for firing GENERATION AND APPLICATION OF HEAT. 67 dental enamels and porcelains, and for continuous-gum work, has been used successfully by the inventor for several years, and ranks among the best of its kind for the purposes indicated. The following abstract, taken from a paper read before the Society for the advancement of Oral Science, and subsequently published, with illustrations, in " Items of Interest," is descrip- tive of the appliance under consideration :— " The furnace shown in Figures 39 and 40 will give a heat from a dull red to a light so bright that an object in the muffle is invisible. Looking at the figures will enable any dentist, by means of the following brief description, to make a similar one : The furnace consists of a cylinder of sheet iron ten inches in diameter and eleven inches high. It has a handle and an iron Fig. 39. Fig. 40. door. The cover is a similar cylinder, two inches deep. Both are lined with porous fire-clay, two inches thick. The furnace walls have four holes in them. Three of these, holes give pas- sage to three tuyeres, the fourth is for a No. 3 muffle, the mouth of which is closed by an iron door lined with asbestos. The door is perforated by a platinum tube, through which passes the platinum trial rod, with a small spoon end for the test piece. This rod can be withdrawn from rime to time, to look at the test piece. At the front of the furnace are two iron tubes, one for gas, the other for air. These pass under the fire-clay arch, where they are brought to a yellow heat by the waste gases as they escape through the slit in the top of the furnace. (See Fig. 40.) Each of these tubes divides into three branches at the (>.S MECHANICAL DENTISTRY. back of the furnace, where the gas tubes enter the air tubes. In this way three double tuyeres are made, their mouths corres- ponding with the holes in the furnace. This arrangement is necessary, for if the heated air and gas are allowed to mix before reaching the mouths of the tuyeres these would be destroyed by the intense heat. Fig. 40 is a perpendicular section of the furnace. The course of the heated gases is indicated by the arrows." As matter having intimate relation to the baking of dental porcelain by the means described and illustrated in these pages, the following observations of Dr. Rollins, in discussing the causes of " gasing " in firing mineral teeth, in addition to those offered by Dr. Land on the same subject, will not be without interest to those having the management of furnaces used for ceramic processes in the dental laboratory. He says :— " In my first experiments for making enamels for filling con- spicuous cavities in teeth, difficulty was sometimes found in making the enamel base of a pure translucent white. As the result of somewhat elaborate tests, it was found that the gray or ■ green tint was due to the reduction of some of the lead oxide. A similar difficulty was encountered when the enamel base was fritted with the metallic oxides necessary to give it the shade of the teeth. Here the oxides themselves were reduced. " It, therefore, seemed probable that the so-called gasing in mineral teeth came from a similar cause. "Many experiments and analyses were made to test the matter, and though it is not worth while to give these in detail, one experiment, which is easily tried, will be mentioned: After having made a furnace like the one described, light the gas and open the air valve. When the heat is high enough, put an unbaked tooth into the muffle. When taken out the color will be pure. Now diminish the- oxygen by partly closing the air valve. Put in another unbaked tooth. When this is removed it will be found gased. The same result will follow with the air valve in the same position as in the first experiment, if the supply of gas is increased. In experiments with dental enamels and porcelains, it is advisable to have a slight excess of air in GENERATION AND APPLICATION OF HEAT. 69 Fig. 41. the furnace. Where the color used, as, for example, platinum, yields the proper tint in the metallic state, this precaution is unnecessary, as in these cases the'color has no oxygen to give up." Ferrier's furnace, Fig. 41, a compact and convenient heater designed especially for continuous-gum work, is operated with gas and the air blast of an ordinary foot blower. By this means a heat is generated sufficient to fuse gum body and enamel in a much shorter time than when solid fuel is used in con- nection with coke or anthracite fur- naces. In commendation of this fur- nace, the inventor says: " This furnace, combining cleanliness, utility, simplic- ity, certainty, economy and durability, which is the outcome of years of ex- periments, has been brought to the minimum of difficulty with the maxi- mum for working, for, although only six inches cube, sufficient heat can be produced in from five to ten minutes to fuse the gum body or enamel for continuous-gum facings (or work) for mounting on vulcanite, celluloid or gold." Gas Crucible Furnace Without Blast.—Fig. 42 represents a small crucible furnace that will be found very convenient for melting and refining the precious and more infusible metals employed by the dentist. It takes crucibles up to 2h by '1\ inches outside, and with a three-foot chimney, will melt copper, gold, silver, etc., in about ten minutes, or cast iron in thirty minutes from the time the gas is lighted. The construction of the burner used with this furnace is illustrated by the sectional diagram, Fig. 43, and is thus described: " The gas enters a chamber at the bottom of the burner, through a device similar to a Bunsen burner, mixing with air as it enters, and is burned at the upper ends of a series of concentric tubes, furnishing air spaces alternately 70 MECHANICAL DENTISTRY. with those supplying the mixture of gas and air. The whole. burner is constructed of iron, and will be found better able to withstand an intense heat, more durable and quicker in its operation than the old pattern, with gun-metal tubes. In case metal should be spilled into the burner, it can be easily taken apart for its removal. " Each part of the burner is lettered, and in case of accident, it can be supplied at a small expense, by specifying the letter on the piece desired. " The burner in its present shape is believed to be the most efficient and economical yet devised for furnace purposes." The following instructions in the use of this furnace .should be observed:— " A chimney or stove pipe, 8 or 10 feet high, may be used as a fixture, and the draught partially stopped with a damper or slide when lower temperatures are required, the gas being turned down in proportion; the guide for the proper adjust- ment being that under all circumstances the flame must GENERATION AND APPLICATION OF HEAT. 71 just cover the crucible or muffle, but not extend into the chimney so as to make it red hot. When the flame covers the crucible or muffle the gas is doing its extreme duty under the most favorable circumstances, without waste. Particles of flux should not be allowed to fall on the fire-clay casing, where the parts touch each other; and the power of the furnace should not be urged too far by the use of very long chimneys, as there is danger of the fusion of the fire-clay parts together, so that they cannot be separated. Fire-clay fittings, as a rule, cannot be safely used for temperatures much exceeding the fusing point of cast iron. Plumbago fittings and crucibles must be heeded slowly the first time they arc used. After the first time they may be subjected instantly to the full power of the furnace without injury." Fig. 44. Gas Crucible Furnaces witli Blast.—A small, compact, and con- venient crucible furnace is shown in Fig. 44. Of this simple but powerful heating apparatus, which will be found especially adapted to the necessities of the dental laboratory, the manu- facturers * observe:— " Owing to the discovery, by Mr. Fletcher, of a singularly perfect non-conducting furnace casing, we are enabled to pro- duce the first really simple gas furnace ever constructed. This material is only about one-sixth the weight of fire clay, and has not one-tenth its conducting power for heat." The furnace consists of a simple pot—for holding the crucible —with a lid, and a blowpipe, all mounted on a suitable cast- iron base. As compared with the ordinary gas furnace it ap- pears almost a toy, owing to its great simplicity. * Buffalo Dental Manufacturing Company. 72 MECHANICAL DENTISTRY. The casing holds the heat so perfectly that the most refrac- tory substances can be fused with ease, using a common foot blower. Half a pound of cast iron requires from 7 to 12 minutes for perfect fusion; the time depending on the gas supply and pressure of air from the blower. The power which can be obtained is far beyond w7hat is re- quired for most purposes, and is limited only by the fusibility of the crucible and casing. The crucible will hold about ten ounces of gold. An ordinary gas supply pipe T56 or f will work it efficiently. It requires a much smaller supply of gas than any other furnace known. About ten cubic feet per hour is sufficient for most purposes. Crucibles must not exceed 21 by 2 inches. Any common blowpipe bellows will work the furnace satisfactorily except for very high temperatures (fusion of steel, etc.), for which a heavy pressure of air is necessary. In adjusting this furnace for use, put the gauze nozzle of the burner closely against the hole in the side of the casing, turn on the gas and light it in the furnace. Work the bellows and then put the cover on the furnace. The air supply should be such that a flame about two inches long will play out of the hole in the cover, and it may be adjusted by turning the thumb- screw on the side of burner. The amount of air and gas used by this burner is very small. Care should be taken that the right proportion of each should be used. A very light but steady blast of air will give the best results. A modified pattern of the foregoing furnace (Fig. 45) has GENERATION AND APPLICATION OF HEAT. 73 been designed, retaining all the peculiar advantages of the one just described, but burning refined petroleum instead of gas, as fuel, and is claimed to be equally as efficient as the gas furnace. The burner for this furnace is constructed upon the principle of an atomizer; and this, of course, dispenses with a wick. This method has proved the most efficient of any that has been ex- perimented with. The recent improvements consist in a device for regulating the supply of oil, which is operated by the milled nut (marked A) shown on top of the reservoir in the cut, and the addition of an annular jet of air, which is regulated by turning the sleeve (marked B). Fig. 47. This burner is so made that it can be taken apart and cleansed, in case there should be any obstruction to its proper working. Remove the burner from the reservoir, by unscrew- ing the small screws; draw out the oil tube, which is operated by the milled nut A, take off the sleeve B, and remove the inside tube. The same furnace and stand are used for either gas or petro- leum, the lamp being fitted for adjustment in place of the gas burner, so that the same apparatus can be furnished for burn- ing either gas or refined petroleum. There is no doubt that these furnaces will become a necessity in every workshop, as they fill a place intermediate between a blowpipe and a large furnace; whilst their strength, cheap- 74 MECHANICAL DENTISTRY. ness, simplicity,, and general usefulness recommend them to all. Fig. 46 represents an ingeniously constructed crucible fur- nace designed by Dr. Rollins, the inventor of the baking, or gas muffle furnace exhibited in Fig. 39. It will appear, from the description, that it is operated with a hot-air blast, a contrivance that greatly augments its heat-producing power. The construc- tion of the furnace is thus described :— Fig. 46 is a section through the furnace. This consists of a pot of porous fire clay, Ca, with cover, Co, of the same material. Between the lip of the cover and the pot is an opening through which the waste gas escapes, surrounding on its way the tubes A and G for air and gas. Fig. 48. Fig. 47 is from a photograph of the furnace. G is the gas tube, A is the air tube. Both are attached by rubber tubes to the gas and air mains. W W are two cups filled with water, which prevents the tubes G and A, which are white hot under the cover C, from burning the rubber tubes where they are at- tached at A and G. As before mentioned, the tubes A and G pass under the cover and appear again on the other side, where the tube G enters the tube A, forming a tuyere, the mouth of which fills the opening through the wall of the furnace pot. In these respects the furnace is simply a small blast furnace. The gas and air remain apart till they enter the mouth of the tuyere, when they unite and, passing up on all sides of the crucible, Cr, Fig. 4(1, go over its top and escape under the cover, GENERATION AND APPLICATION OF HEAT. (O passing all around the gas and air tubes which they heat white hot. This furnace, like others of its class, is worked with the ordi- nary illuminating gas and bellows. Of this contrivance the inventor says: " The furnace is so simple that any one can construct it for himself. Indeed, this is probably the only way in which it can be had, as the makers of dental supplies do not usually care to place any article on the market unless they can be protected by a patent." An approved crucible furnace of recent introduction, known as Fletcher's injector gas furnace, is shown in Fig. 48. Of this heating apparatus Prof. Essig* says: " The construction of this apparatus is upon the principle of the injector furnace, and it is claimed that its power and speed of working are practically without limit, depending only upon the gas and air supply. With a half-inch gas pipe and the small foot blower this fur- nace will melt a crucible full of cast-iron scraps in ten minutes. The supply of gas required is exceedingly small. Allowing five cubic feet of gas for heating up, it consumes about four feet of gas for every pound of cast iron melted, and for laboratory purposes it is the cheapest and most convenient furnace in use. It is very simple in construction, and consists of two parts, an upper portion, which forms the cover, and a lower part, which holds the crucible while in operation." A very useful and almost indispensable heating apparatus in the dental laboratory, suitable for drying, boiling, melting metals requiring a moderate temperature, FlG 49 as zinc, tin, lead, etc., heating flasks pre- paratory to packing with rubber, and a variety of other purposes, is exhibited in Fig. 49. The burner, consisting, as will be seen, of a circular perforated gas tube, with a central air jet, gives a complete range of temperature, from a gentle current of warm air to a clear red heat, and is so perfectly •under control, that a common glass bottle may be placed on * Dental Metallurgy, p. 77. \ 76 MECHANICAL DENTISTRY. the tripod and heated to any required temperature without the slightest risk of fracture. For very low temperatures the ring must be lighted through the opening B. This gives a steady current of heated air through the gauze above. For boiling, melting, etc., the light must be applied on the surface of the gauze, thereby providing a large body of blue flame, which can be urged by the blast pipe C. This is one of the most generally useful burners, and stands hard dirty work without injury. The gauze, if choked up with dirt, can be replaced in a few seconds. An equally convenient heater for many purposes requiring a diminished temperature as compared with the air-blast heater just described, is exhibited in Fig. 50. A gentle current of air passes through side openings in the end of the injecting tube, mingling with the gas supplied through a rubber tube attached to an ordinary gas burner. An admirably contrived ladle fur- nace, designed by Dr. Fletcher, is shown in Fig. 51. This simple con- trivance, provided with a heating apparatus similar to the burner last described, is especially well adapted for melting any of the several metals usually Fig. 51. employed for dies and counter-dies, as zinc, tin, lead, Babbitt metal, etc. The burner can be removed from the casing and GENERATION AND APPLICATION OF HEAT. / 7 used for other purposes if desired. A cast-iron ladle of suit- able form, with a detachable handle, which can be removed during the process of melting, is also illustrated. CRUCIBLES. Crucibles are small, conical-shaped vessels used by the dentist principally for the purposes of melting and refining metals used for plates, compounding metallic alloys, preparing and com- pounding the various ingredients employed in the manufacture of porcelain teeth and continuous-gum work, etc. They com- bine in a high degree the properties of infusibility, exemption from the attack of substances fused in them, the power of resist- ing sudden alternations of temperature, and impermeability to fluids and gases. The Hessian crucibles, which are in most common use among dentists, are composed of silica, alumina, and oxide of iron. Plumbago crucibles are also made from special patterns, and expressly designed for Fletcher's furnaces. For a more particular description of the various components entering into the structure of crucibles, as well as the manner of manufacturing them, the reader is referred to Piggot's Den- tal Chemistry and Metallurgy, and other works treating more fully of the subject. To avoid a possible loss of fused metals which may occur in consequence of some imperfection in the crucible, a test trial should first be made by placing in it a small quantity of borax and then subjecting it to a high heat. If imperfect, the borax, rendered semi-fluid by the heat, will pass through the sub- stance of the crucible and glaze the surface on the outside. CHAPTER III. METALS EMPLOYED IN DENTAL LABORATORY OPERATIONS. GOLD. Gold has been known from a period of great antiquity, hav- ing, according to the writings of Moses, been wrought into articles of jewelry more than three thousand years ago. As a base or support for artificial dentures, it has entirely superseded the use of the various animal substances formerly employed, and, by the mass of practitioners at the present time, it con- tinues to be the most highly esteemed metal for the purpose mentioned, notwithstanding the more recent introduction of processes in which, as a base, this metal is wholly dis- carded. Gold is found only in the metallic state, and occurs either crystallized in the cube, and its allied forms, or in threads of various sizes, twisted and interlaced into a chain of minute octahedral crystals; also in spangles or roundish grains. These latter, when they occur of a certain magnitude, are called pepitas, some specimens of which have been obtained of great size. In 1810 a mass of alluvial gold weighing twenty-eight pounds was found in the gravel pits of the creeks of Rockhole, in North Carolina. A lump of gold ore weighing three cwt. was forwarded from Chili, South America, as a contribution to the World's Exhibition in London. New Granada, California, Russia, and Australia, have each produced pepitas, or masses of gold weighing respectively twenty-seven and a half, twenty- eight, seventy, and one hundred and six pounds. Geological Situations.—The crystalline primitive rocks, the compact transition rocks, the trachytic and trap rocks, and alluvial grounds, are the formations in which gold occurs. Un- like many other metals, it is never in such large quantities as to constitute veins by itself, but is either disseminated through the rocky masses, or spread out in thin plates or grains on their surface, or confined in their cavities in the shape of filaments 78 GOLD. 79 or crystallized twigs. The minerals composing the veins are either quartz, calcspar, or sulphate of baryta. The ores asso- ciated with the gold in these veins are principally iron, copper, arsenical pyrites, galena, and blende. The most abundant sources of gold, however, are in alluvial grounds, where it is found distributed in the form of spangles in the sands of certain plains and rivers, especially at their re-entering angles, at the season of low water, and after storms and temporary floods. Sufficient reasons have been advanced in support of the belief that gold found in alluvial situations belongs to the grounds traversed by these rivers, instead of being washed, as was formerly supposed, from the mountains in which their waters have their origin. Geographical Distribution.—The European mines more par- ticularly distinguished for their richness, are in Hungary and Transylvania, especially the former. Gold also occurs, but more sparingly, in Ireland, Sweden, Siberia, Germany, Russia, Spain. In Asia and Africa, the mines which yield most abun- dantly are situated in the southern portions of these continents. From the latter, the ancients derived the greater portion of their gold. Several of the South American provinces yield this metal in considerable quantities. Washings are also common in several States of the Union, but California stands unrivaled, except by Australia, in the immense productiveness of its mines, and its resources in respect to this rare and valuable metal are reckoned inexhaustible. Properties of Gold.—Pure gold is distinguished from all other metals by its brilliant orange-red or yellow color, being the only simple metal that possesses this complexion. It is sus- ceptible of a high polish, but is inferior in brilliancy to steel, silver, or mercury. Its specific gravity varies somewhat, accord- ing as it is fused or hammered ; the former having a density of 19.26; the latter ranging from 19.4 to 19.65. It is only ex- celled in density, therefore, by platinum, the specific gravity of which is 21.25. Gold surpasses all other metals in malleability. The average thickness of ordinary gold leaf is ?82W of an inch, but the ultimate degree of attenuation of which pure gold is susceptible 80 MECHANICAL DENTISTRY. exceeds considerably this estimate. It is also distinguished for its ductility. A single grain of gold may be drawn into wire 500 feet in length, while an ounce may be made to extend 1300 miles. It is somewhat softer than silver, and possesses great tenacity, though inferior in this quality to iron, copper, platinum or silver. A thread of gold T%fo of an inch in diameter will sustain a weight of 150 pounds. Gold fuses at 2016° with con- siderable expansion, and on cooling, contracts more than any other metal. On account of the want of affinity of gold for oxygen, it remains unaltered in the longest exposure; it is incapable of being oxidized in any heat that may be applied to it, and is only volatilized with great difficulty in the resistless heat of the oxy-hydrogen blowpipe. It is unaffected by the most concen- trated of the simple acids, but is readily soluble in aqua regia or nitro-muriatic acid, and nitro-fluoric acid. It will thus be seen that gold possesses, in an eminent degree, those general properties which render it peculiarly fit for the purposes to which it is applied in the practice of dental pros- thesis. Influence of Alloying on the Properties of Gold.—The term alloy signifies a compound of any two or more metals, as brass, which is an alloy of copper and zinc. Alloys, in respect of their uses, are practically new metals, and differ in many important respects, both in their chemical and physical characteristics, from the constituent metals of which they are composed. A more particular account of the influence of alloying upon the general properties of metals, and their management and behavior in the process of compounding, will be given under the head of alloys of the baser metals. As gold combines readily with most metals, some of the more prominent conditions which distinguish its alloys will be given. The malleability of gold is, strictly speaking, always impaired by its union with other metals. This effect is eminentlv characteristic of certain contaminations, as those with arsenic tin, antimony, bismuth, lead, etc.; while with certain other metals, as silver, copper, and platinum, unless in excess, this GOLD. 81 property of gold is so little affected, as in no material degree to interfere with its being worked into any desired form for den- tal purposes. The ductility of gold is also usually diminished by its incorporation with foreign metals; sometimes in a re- markable degree. Gold is always rendered harder, and its tenacity is generally increased, by alloying, while its density varies with the particular metal or metals with which it is combined. Thus, the alloy of gold with either zinc, tin, bis- muth, antimony or cobalt has a density greater than that of the mean of its constituents, while the alloys of gold having a less specific gravity than the mean of their components are those with silver, iron, lead, copper, iridium or nickel. Gold is ordinarily more fusible when alloyed, the alloy always melt- ing at a less heat than that required to fuse the most refractory constituent, and oftentimes less than the more fusible com- ponent. The alloy of gold and platinum furnishes an example of the former; the platinum, which in its uncombined state is infusible in the highest heat of a blast furnace, forming a fusible compound with gold, the melting point of which is far below that of platinum. Gold solder, composed of gold, copper, and silver, affords a familiar illustration of the latter, the alloy melting at a less heat than that required to fuse its least refrac- tory component, silver. Gold, which in its pure state has less affinity for oxygen than any other metal, is rendered more or less oxidizable when combined with other metals. That gold alloys tend to be formed in definite proportions of their constituents would appear from the phenomenon observed in the native gold of the auriferous sands, which is an alloy with silver in the ratio of 1 atom of silver, united to 4, 5, 6, 12 atoms of gold, but never with a fractional part of an atom. The same circumstance is noticed in connection with the amalgam of silver and mercury. But as alloys are generally soluble in each other, the definiteness of this atomic combination is obscured and disappears in most cases. Properties of Particular Alloys of Gold.—The metals with which gold is liable to be contaminated in the dental labora- tory are zinc, tin, lead, antimony, bismuth, iron or steel, mer- cury, and arsenic; as also excess of silver, copper, and platinum. 6 82 MECHANICAL DENTISTRY. As several of these metals when alloyed with gold, even in very minute quantities, are highly destructive in their influence upon those properties which adapt this metal to the various wants of the mechanical operator, and as their separation is often attended with considerable difficulty, annoyance, and loss of time, it is practically important that care should be taken to prevent, as far as practicable, the admixture of any one or more of them with the gold scrap, filings, or sweepings that are to be re- converted into proper forms for use. The accidental intrusion of these metals, however, is, to some extent, unavoidable, and as an acquaintance with the more prominent characteristics or sensible properties of the resulting alloys sometimes furnishes valuable indications in the selection of the proper reagents em- ployed in their purification, a description of individual alloys is introduced. Tin, antimony, bismuth, lead, and arsenic, are peculiarly promi- nent in their effects upon the malleability of gold; either of these metals in exceedingly minute quantities rendering gold intractable. One part of antimony with nine parts of gold, form a pale, brittle alloy, and in the proportion of one part of the former to 1920 of gold, the resulting compound is too brittle to admit of successful lamination. An alloy of arsenic with gold containing ^\^ of the former is a gray, brittle metal, while in the proportion of 9^, the mallea- bility of the gold is seriously impaired without suffering any change of color. So energetic is the influence of this metal on gold that the latter is rendered brittle when subjected even to the vapor of arsenic. Tin, lead, and bismuth are somewhat analogous to arsenic in their influence upon the malleability of gold, either of them, in almost inappreciable quantities, rendering the latter metal un- manageable under the rollers. One part of lead or bismuth to 1920 of gold converts the latter into an unmalleable metal, while tin exceeds either in its remarkable tendency to render gold hard and brittle. Alloys of gold with tin are of a light color; those with lead are of a darker complexion. Zinc with gold forms a brittle alloy, and when combined in GOLD. 83 equal proportions is exceedingly hard, white, and brittle. Uniting or incorporating itself less intimately with the gold than either lead or tin, however, it not unfrequently happens that portions of the ingot will be brittle while others remain, in some degree, malleable; so that the bar, when rolled out in the form of plate, will be perforated or cracked at those points where the zinc preponderates, while remaining portions of the plate retain a moderate degree of softness and pliability. The working properties of gold are not sensibly affected by the incorporation of very small quantities of iron, as an alloy of these metals, in the proportion of one part of the latter to eleven of gold, remains malleable. Platinum, in itself a highly refractory metal, is, as before stated, rendered fusible in combination with other metals. When combined with gold in small proportions, the latter is rendered harder and more elastic without having its mallea- bility practically impaired. Platinum very readily affects the color of gold, the smallest quantities rendering the alloy pale and dull-colored. Silver unites with gold in every proportion, and is the chief metal employed in the reduction of gold to the required forms for dental uses. It renders gold more fusible, and imparts to it increased hardness without materially affecting its mallea- bility. The alloy is light-colored in proportion to the amount of silver introduced. Copper, like silver, is usually combined with gold in the formation of plate, solders, etc., and hardens and renders gold tougher without practically impairing its malleability. It im- parts to the alloy a deeper red color, and the form of plate is capable of receiving a polish excelling in richness and brilliancy any other metal. The foregoing alloys of gold, it will be perceived, are such as result from the incorporation with gold of minute propor- tions of any one of the base metals mentioned, and possess certain physical characteristics that indicate, with tolerable certainty, the particular alloying component. Thus, for ex- ample, if the alloy is light-colored and very brittle, the pres- ence of tin may be suspected; if brittle and dull-colored, lead 84 MECHANICAL DENTISTRY. is indicated; if grayish or dull-colored, but still malleable, tough and elastic, platinum is probably present; if unequally malleable, or brittle in spots, the presence of zinc may be inferred. Alloys of gold, however, embracing several or all of these metals in varying proportions, are sometimes accidentally formed, in which case the more distinctive features which characterize the binary compounds are lost or obscured. CHAPTER IV. REFINING GOLD. Elements Employed.—The separation of foreign metals from gold by what is termed the "dry method," or roasting, is effected by the action on them of either oxygen, chlorine, or sulphur, converting them into oxides, chlorides, or sulphurets. Certain compound substances are used for this purpose which, when heated and decomposed, yield these elements in sufficient quantities for the purposes specified. The refining agents in common use are nitrate of potassa (nitre, or saltpetre), which yields oxygen; chloride of mercury (corrosive sublimate), which yields chlorine; and sulphuret of antimony (crude antimony), which yields sulphur. Other compounds contain these ele- ments, but those mentioned are generally preferred because they contain them abundantly, are readily decomposed by heat, and do not materially interfere with the process of separa- tion by the introduction of troublesome components into the alloy. Before considering specifically the different modes of refining alloys of gold, it will be convenient to classify the different forms of gold as they occur in working this metal in the laboratory. 1. Plate-scrap or clippings, and plate-filings. These, if proper care is taken to prevent the introduction of fragments of platinum, impure filings, or particles of base metals, only require, provided they were originally of suitable fineness, to be remelted and again converted into plate or other forms for use. 2. Mixed filings, and fragments containing solder, platinum, etc. These, when melted alone, produce an alloy more or less impoverished in proportion to the quantity and quality of the foreign metals introduced in finishing pieces constructed of gold, and should either be separately refined by roasting, or reduced to pure gold by the " humid method," to be described hereafter. 85 86 MECHANICAL DENTISTRY. 3. Sweepings. This form embraces many impurities, earthy and metallic, and should first be thoroughly washed, to remove the earthy constituents, after which the remaining metals may either be mixed with class second, or separately refined. Another, and perhaps better, method, is to fuse together the sweepings and substances hereinafter mentioned, in the follow- ing proportions: Of sweepings, eight parts; chloride of sodium, four parts; impure carbonate of potassa, four parts; impure supertartrate of potassa, one part; and nitrate potassa, half part. Mix them thoroughly together, and melt in a crucible. The crucible with its contents should remain in the fire for some time, in order to secure a complete separation of the metals from extraneous matter. It is evident from the above classification that much time and labor may be saved by preserving these forms of gold separately as they accumulate in the shop. Separate lap-skins or receptacles, therefore, should be appropriated to the working of gold, one to receive scrap and unmixed plate-filings, which may be re-converted into plate without refining; another to collect the solder-filings, and such impure fragments as require purification. Separation of Foreign Metals from Gold.—The most trouble- some ingredients which find their way into gold alloys are what are commonly called base metals, as tin, lead, zinc, iron, antimony, bismuth, etc. In attempting to separate these metals from gold, it is not a matter of indifference what reagent is employed, inasmuch as distinct affinities exist, which may be advantageously consulted. If, for example, zinc or iron, or both of these metals are present in small quantities, any com- pound which yields oxygen will, by virtue of the affinity of the latter for these metals, effect their separation by converting them into oxides, hence, when these metals are to be got rid of, nitrate of potassa is employed. But oxygen has but a feeble affinity for tin, and when this metal is present, its separation is better effected by some compound which parts with chlorine in the act of decomposition; chloride of mercury is therefore used for the purpose. When the alloy of gold contains a number of these metals at the same time, and is very coarse, sulphuret REFINING GOLD. 87 of antimony, which is a very powerful and efficient reagent, should be resorted to, unless the operator should prefer, and which is the better way, to reduce the alloy to pure gold by the " humid method." After all traces of iron or steel have been removed from the gold fragments and filings by passing a magnet repeatedly through them, the latter should be placed in a clean crucible, lined on the inside with borax, and covered either with a piece of fire-clay slab, or broken crucible. Sheet-iron has been recommended for the latter purpose, but should never be used, as, when highly heated, scales form on the surface, and are liable to drop in upon the fused metals. If the operation of roasting is likely to be protracted, an inverted crucible, with a hole in the bottom, may be securely luted to the top of the one containing the metals; the refining agents and fluxes being introduced through the opening in the upper crucible. These are then placed in the furnace, on a bed of charcoal, or what is better, a mixture of charcoal and coke, the latter being built up around the crucible, and over it when covered with a second crucible, care being taken that no fragments of fuel are per- mitted to fall in upon the fused metals. Small portions of borax may first be added, and when the metals are fluid, the refining agents may be introduced in small quantities from time to time, and the roasting continued from half an hour to an hour, according to the coarseness of the alloy. The roast- ing may be conducted first with borax and nitre, to effect partial separation, when the crucible may be removed from the fire and the metals allowed to cool gradually. The crucible may then be broken, and the button of gold at the bottom removed and separated from the slag that covers it with a hammer. The button is then put into a fresh crucible and re- melted. If there is any known base metal present likely to render the gold brittle, the particular reagent which will most readily attack it may now be used. If, however, as is generally the case, the alloy is of uncertain composition, or contains various metals having distinct affinities, the process becomes, to some extent, experimental, and it may become necessary to use first one refining agent and then another, until sufficient 88 MECHANICAL DENTISTRY. separation is effected. Generally, it will be sufficient to use the nitrate of potassa alone, as most metals are oxidable. After roasting with nitre for half or three-fourths of an hour, adding small portions at a time, the melted metals may be poured into ingot molds previously warmed and oiled. If, after hammer- ing, annealing, and rolling the ingot, it should still be found brittle, it must be remelted, and chloride of mercury used as the refining agent. This will remove any traces of tin which may be present. If the alloy, however, is greatly impoverished, it may be more advantageously treated with sulphuret of antimony; in which case the metal should be melted in a large crucible with about twice or three times its weight of the native sulphuret, which should be added in small quantities at a time. The heat decomposes the sulphuret of antimony; the sulphur unit- ing with the base metals forming sulphurets, and the antimony uniting with the gold forming a leaden-colored alloy. The antimony may be parted from the gold alloy in the following manner: Place the mixture in a clean crucible, and, when melted, force a current of air with a pair of bellows upon its surface; this oxidizes the antimony, which passes off in the form of vapor. The current should be mild at first, as too great a draught is apt to carry off portions of gold by a too hurried volatilization of the antimony. A current strong enough to produce visible fumes will be sufficient. When these cease, the crucible may be covered, and as the melting point of the gold rises with the escape of antimony the fire should be urged to a stronger heat, and before pouring, a forcible current of air should again be thrown upon the surface of the melted metals to effectually dissipate any remaining portions of the antimony. If, after treatment with the reagents enumerated, the alloy should be found malleable, but stiff or elastic, and dull-colored, it is probably due to the presence of; platinum; and any further attempts to reduce it by roasting will prove unavailing. It must then be subjected to the process which will be hereafter described for the separation of gold and platinum. When it is desired to reduce the alloy to pure gold, which is REFINING GOLD. 89 generally advisable whenever the gold to be refined consists of very coarse filings, fragments of plate containing large quantities of solder, linings with platinum pins attached, particles of base metals, etc., the "humid process," as it is called, should be employed. The solvents in common use for this purpose are nitric, sulphuric, and nitro-muriatic or hydrochloric acid; but as the desired results can be more conveniently and directly obtained by the use of the latter, or hydrochloric acid, this most available method alone will be given. The following practical remarks on the process are copied from an article on the " Management of Gold,"* by Professor George Watt. " When the alloy is composed of metals differing but little in their affinities for oxygen, chlorine, etc., we resort to one of the ' wet methods.' And, in connection, we will only describe the one which we consider the most convenient and effectual for the practical dentist. It is effectual in all cases, as it always gives us pure gold. " Let us, then, suppose that our gold alloy has become con- taminated with platinum to such extent that the color and elasticity of the plate are objectionable. The alloy should be dissolved in nitro-muriatic or hydrochloric acid, called aqua regia. The best proportions for aqua regia are three parts of hydrochloric acid to one of nitric. If the acids are at all good, four ounces of the aqua regia will be an abundance for an ounce of the alloy. The advantage of using the acids in the propor- tion of three to one, instead of two to one, as directed in most of the text-books, is, that when the solution is completed, there is but little, if any, excess of nitric acid. If the acids be ' chemically pure,' four parts of the hydrochloric to one of the nitric produces still better results. " By this process the metals are all converted into chlorides; and, as the chloride of silver is insoluble, and has a greater specific gravity than the liquid, it is found as a grayish-white powder at the bottom of the vessel. The chlorides of the other metals, being soluble, remain in solution. By washing and pouring off, allowing the chloride of silver time to settle to the bottom, the solution may be entirely separated from it. * Dental Register of the West, vol. xii, p. 251. 90 MECHANICAL DENTISTRY. " The object is now to precipitate the gold while the others remain in solution. This precipitation may be effected by any one of several different agents, but we will mention only the protosulphate of iron. " This salt is the common green copperas of the shops, and, as it is always cheap and readily obtained, we need look no further. It should be dissolved in clean rain-water, and the solution should be filtered, and allowed to settle till perfectly clear. Then it is to be added gradually to the gold solution as long as a precipitate is found, and even longer, as an excess will the better insure the precipitation of all the gold. The gold thus precipitated is a brown powder, having none of the appearances of gold in its ordinary state. The solution should now be filtered, or the gold should be allowed to settle to the bottom, where it may be washed after pouring off the solution. It is better to filter than decant in this case, as, frequently, particles of the gold float on the surface, and would be lost in the washings by the latter process. " Minute traces of iron may adhere to the gold thus precipi- tated. These can be removed by digesting the gold in dilute sulphuric acid; and, when the process is properly conducted, thus far, the result is pure gold, which may be melted, under carbonate of potash, in a crucible lined with borax, and reduced to the required carat." CHAPTER V. ALLOYS OF GOLD FOR DENTAL PURPOSES. Gold in its pure state is rarely employed by the dentist in laboratory processes, on account of its softness and flexibility; it is, therefore, usually alloyed with such metals as impart to it —without practically impairing either its malleability, pliancy or purity—the degree of hardness, strength and elasticity neces- sary to resist the wear and strain to which an artificial piece constructed from it is unavoidably exposed in the mouth. Reducing Metals.—The metals with which gold is usually combined are copper and silver. It is sometimes reduced with silver alone, many regarding the introduction of copper into the alloy as objectionable, as plate derived from it is supposed to be more readily tarnished and to communicate to the mouth a disagreeable metallic taste. This is unquestionably true, if, as is sometimes the case, the copper used is in excess; when, in addition to the effects mentioned, gold, so debased, may become a source of positive injury to the organs of the mouth, as well as to the general health. The small proportions of copper usually employed in forming gold plate, however, is not likely to produce, in any objectionable degree, the consequences com- plained of, unless the fluids of the mouth are greatly perverted. If gold coin is used in the formation of plate, it maybe sufficient to add silver alone, inasmuch as copper is already present; though, usually, additional quantities of the latter metal are added. Required Fineness of Gold Plate.—Alloys of gold to be perma- nently worn in the mouth should be of such purity as will most certainly, under all the contingencies of health and dis- ease, resist any chemical changes that would tend to com- promise either the comfort or health of the patient. Evils of no inconsiderable magnitude are sometimes inflicted, either through ignorance, carelessness or cupidity, by disregard of this important requirement. If the general health of the patient remained always uniformly unimpaired, with the secretions of the mouth in their normal state, gold degraded to eighteen or 91 92 MECHANICAL DENTISTRY. even sixteen carats fine, would undergo no material changes in the mouth. But it must be remembered that, in addition to the corrosive agents introduced into the mouth from without, a variety of diseases, local and constitutional, effect important changes in the otherwise bland and innoxious fluids contained therein, which, from being alkaline or neutral, become more or less acidulated. Indigestion, with acid eructations; gastro- enteritis ; ague; inflammatory and typhoid fevers; brain affec- tions ; eruptive diseases; rheumatism; gout, etc., are some of the local and constitutional disorders almost uniformly impart- ing to the mucous and salivary secretions an acid reaction. When this condition of the secretions exists in connection with the use of gold readily acted on chemically by reason of its impoverishment, some degree of irritation of the tissues of the oral cavity is likely to ensue. Gold plate intended to be intro- duced into the mouth should not, therefore, as a general thing, be of a less standard of fineness than from eighteen to twenty carats. It may exceed this degree of purity in some cases, but will rarely or never, unless alloyed with platinum, admit of being used of a higher carat than the present American coin, which is 21.6 carats fine. Formulas for Gold Plate used as a Base for Artificial Den- tures.—Any of the following formulas may be employed in the formation of gold plate to be used as a base or support for artificial dentures. The relative proportions of the alloying components may be varied to suit the peculiar views or ne- cessities of the manipulator. The estimated carat of the ap- pended formulas are based on the fineness of the American gold pieces coined in 1837 and thereafter. GOLD PLATE EIGHTEEN CAEATS FINE. Formula No. 1. Formula No. 2. 18 dwts. pure gold, 20 dwts. gold coin, 4 dwts. fine copper, 2 dwts. fine copper, 2 dwts. fine silver. 2 dwts. fine silver. GOLD PLATE NINETEEN CAEATS FINE. Formula No. 3. Formula No. 4. 19 dwts. pure gold, 20 dwts. gold coin, 3 dwts. copper, 25 grs. copper, 2 dwts. silver. 40 -f grs. silver. ALLOYS OF GOLD FOR DENTAL PURPOSES. 93 GOLD PLATE TWENTY CAEATS FINE. Formula No. 5. Formula No. 6. 20 dwts. pure gold, 20 dwts. gold coin, 2 dwts. copper, 18 grs. copper, 2 dwts. silver. 20+ grs. silver. GOLD PLATE TWENTY-ONE CAEATS FINE. Formula No. 7. Formula No. 8. Formula No. 9. 21 dwts. pure gold, 20 dwts. gold coin, 20 dwts. gold coin, 2 dwts. copper, 13+ grs. silver. 6 grs. copper, 1 dwt, silver. 7^ grs. platinum. GOLD PLATE TWENTY-TWO CAEATS FIXE. Formula No. 10. 22 dwts. pure gold, 1 dwt. fine copper, 18 grs. silver, 6 grs. platinum. The union of platinum with gold, as in Formula No. 10, furnishes an alloy rich in gold, while it imparts to the plate derived from it a reasonable degree of stiffness and elasticity; preserves in a good degree the characteristic color of fine gold ; and does not materially impair its susceptibility of receiving a high polish. The amount of gold coin given in Formula No. 9 may be reduced with platinum alone, adding to it from eight to twelve grains; in which case, although the carat of the alloy is lowert,.!, its absolute purity remains unaffected, and plate formed fVom it will better resist any changes in the mouth than gold coi/n itself. Formulas for Gold Plate used for Clasps, Wire, Stays or Linings, Met all. he •Pivots, etc.—Gold used in the formation of clasps, stays, etc., is improved for these purposes by the addition of sufficient platinjum to render it firmer and more elastic than the alloys ordinairily employed in the formation of plate as a base. The advantages of this elastic property, in its application to the purposes under consideration, are, that clasps formed from such alloyx will adapt themselves more accurately to the teeth, as, when partially spread apart on being forced over the crowns, they vill spring together again and accurately embrace the more 'contracted portions. In the form of stays or backings, additi-onal strength being imparted, a less amount of substance will b required; the elasticity of these supports, also, will not 94 MECHANICAL DENTISTRY. only lessen the chances of accident to the teeth themselves in mastication and otherwise, but preserve their proper position when temporarily disturbed by any of the forces applied to them. The same advantages last mentioned are obtained from this property in the use of metallic pivots. Formula No. 1. Formula No. 2. 20 dwts. pure gold, 20 dwts. coin gold, 2 dwts. fine copper, 8 grs. fine copper, 1 dwt. fine silver, 10 grs. silver, 1 dwt. platinum. 20 grs. platinum. The alloy derived from either of these formulas will be twenty carats fine. Gold Solders.—Solders are .a class of alloys by means of which the several pieces of the same or of different metals are united to each other. They shouldxl?e more fusible than the metals to be united, and should consist W such components as possess a strong affinity for the substances \to be joined. They should also be as fine as the metals to whicrK they are applied will admit of without endangering the latter. Solders of different degrees of fineness, therefore, should ;always be pro- vided, from which the one most suitable for any given case may be selected. The use of solders of doubtful or unknown composition should be avoided, and hence they should be confounded either from pure gold or gold coin. \ The following formula taken from Prof. Harris's work on Dental Surgery, page 664, recipe No. 3, may be used in connec- tion with eighteen or twenty carat gold plate, and is' sixteen carats fine:— 6 dwts. pure gold, 2 dwts. roset copper, 1 dwt. fine silver. Recipes Nos. 1 and 2, page 663 of same work, are too coarse to be introduced into the mouth; the former being a fraction below fourteen carats, while the latter is still more objectionable, exceeding but little twelve and one-half carats. Formula No. 1 of the following recipes is a fraction over fifteen carats fine; and No. 2 furnishes a solder eighteen carats fine:— ALLOYS OF GOLD FOR DENTAL PURPOSES. 95 Formula No. 1. Formula No. 2. 6 dwts. gold coin, Gold coin, 30 parts. 30 grs. silver, Silver, 4 " 20 grs. copper, Copper, 1 " 10 grs. brass. Brass, 1 " In the reduction of gold for solders, Dr. Dorrence recom- mends the use of what he calls " solder alloy." This is derived from the following formula:— 1 part pure silver, 2 parts pure zinc, 3 parts pure copper. The copper and silver are melted without flux, in a clean crucible which is well lined with borax ; the zinc is then added in small quantities as rapidly as may be without chilling the molten mass so that it loses its fluidity, meanwhile stirring it with a clay pipe-stem or rod, or a white-wood stick, until the profuse fumes of the burning zinc just pass off, when pour immediately into an ingot mold, or into clean water in a clean wooden pail. The metals entering into the composition of this solder alloy should be absolutely pure, especially should they be free of arsenic, antimony, cadmium, etc., in which case not only the alloy, but gold and silver solders made from it, will be tough and easy-flowing. Inasmuch as the zinc, in com- pounding the alloy, has not been protected from oxidation, if it has been cast at the proper moment, it will be found present in about its combining weight. Both gold and silver solders made with this alloy will, as has been stated, be found very tough and easy-flowing, the range of proportion most desirable being, for gold solder, from 20 to 12 carats, or from 15 to 50 per cent. of alloy. Dr. D. very properly says, however, that the 12 carat or 50 per cent, solder is too coarse for dental work. From 10 to 15 per cent, of the alloy added to gold coin is recommended as a suitable solder in the construction of coin-gold crowns. Zinc, as a constituent of solders, is used principally with a view of rendering them more fusible without materially debas- ing them if the proper proportion is observed. Its employment under any circumstances has been objected to by some, on the ground that the alloy is more readily tarnished in the mouth, is more brittle, and that it furnishes more favorable conditions 96 MECHANICAL DENTISTRY. for galvanic action. These objections only hold good when zinc is used, in excess. When employed in quantities sufficient only to make the gold flow readily and evenly at a diminished heat, it is claimed that the base metal used in these alloys is chiefly consumed in the process of soldering, leaving a residuum of gold alloy equal, or nearly so, in purity to solder not so contami- nated. If such is the case, they are acceptable alloys for solder- ing purposes, inasmuch as it is not only desirable to have an easy-flowing solder, but one which shall have as little affinity as possible for acids often found associated with the fluids of the mouth. Care should be taken to add no more zinc than is necessary to make the solder flow freely under a heat that may be safely applied without danger of melting the pieces to be united. Method of reducing Gold to a lower or higher standard of Fine- ness, and of determining the Carat of any given Alloy.—In the process of compounding gold for dental purposes, the manipu- lator should always aim at exactness in the quantity and rela- tive proportions of the reducing components, and should be able to determine precisely the purity of the metals he employs. Gold alloys are too often arbitrarily compounded, and used without any adequate knowledge of their qualities or properties; and formulas, taken on trust, are employed without any certain knowledge of the quality of the alloys they produce. That we may knowr certainly the quality of the gold alloys used in the laboratory without resorting to the inconvenient process of analysis or assaying, they should always be made either from pure gold or gold coin, the standard of these being definitely fixed. But as the process of procuring pure gold is somewhat tedious and troublesome, gold coin is very generally employed for the purpose. The amount of alloy necessary to reduce either pure or coin gold to any particular standard, whether higher or lower, and the method of ascertaining the carat or fineness of any given alloy, may be readily determined by a few simple rules. The following practical remarks on the method are copied from an article on " Alloying Gold,"* by Professor G. Watt. * Dental Register of the West, vol. x, p. 396. ALLOYS OF GOLD FOR DENTAL PURPOSES. 97 " 1. To ascertain the carat of any given alloy.—-The proportion may be expressed as follows:— " As the weight of the alloyed mass is to the weight of gold it contains, so is 24 to the standard sought. Take, for example, Harris's No. 3 gold solder:— Pure gold..................6 parts. " silver.................2 " " copper.................1 " Total.................. 9 " The proportion would be expressed thus :— 9:6: : 24 : 16. " From this any one can deduce the following— " Rule.—Multiply 24 by the weight of gold in the alloyed mass, and divide the product by the weight of the mass; the quotient is the carat sought. " In the above example, 24 multiplied by 6, the quantity of gold, gives 144, which, divided by 9, the weight of the whole mass, gives 16. Hence, an alloy prepared as above, is 16 carats fine. " As another example, under the same rule, take Harris's No. 1 solder:— 22 carat gold................48 parts. silver...............16 " copper...............12 " Total.................76 " Now, as the gold used is but 22 carats fine, one-twelfth of it is alloy. The one-twelfth of 48 is 4, which subtracted from 48 leaves 44. The statement then is— 76 : 44 : : 24 : 13.9. " This solder, therefore, falls a fraction below 14 carats. " 2. To reduce gold to a required carat.—The proportion may be expressed as follows:— " As the required carat is to 24, so is the weight of the gold used to the weight of the alloyed mass when reduced. The weight of gold subtracted from this, gives the quantity of alloy to be added. " For example, reduce 6 ounces of pure gold to 16 carats. " The statement is expressed thus :— 16 : 24 : : 6 : 9. 7 98 MECHANICAL DENTISTRY. " Six subtracted from 9 leaves 3, which is the quantity of alloy to be added. From this is deduced the following— " Rule.—Multiply 24 by the weight of pure gold used, and divide the product by the required carat. The quotient is the weight of the mass when reduced, from which subtract the weight of the gold used, and the remainder is the weight of alloy to be added. " As another example under the same rule, reduce 1 penny- weight of 22 carat gold to 18 carats. "As the gold is only 22 carats fine, one-twelfth of it is already alloy. The one pennyweight, therefore, contains but twenty-two grains of pure gold. The statement is, therefore, thus expressed— 18 : 24 : : 22 : 29£. " Twenty-two subtracted from 29^ leaves 7£. Therefore, each pennyweight of 22 carat gold requires 7^ grains of alloy to reduce it to 18 carats. "3. To reduce gold from a lower to a higher carat.—This may be done by adding pure gold or a gold alloy finer than that required. The principle of the rule may be set forth in the following general expression :— " As the alloy in the required carat is to the alloy in the given carat, so is the weight of the alloyed gold used to the weight of the reduced alloy required. The principle may be practically applied by the following— " Rule.—Multiply the weight of the alloyed gold used by the number representing the proportion of alloy in the given carat, and divide the product by that representing the propor- tion of alloy in the required carat; the quotient is the weight of the mass when reduced to the required carat by adding fine gold. " To illustrate this, take the following example:— " Reduce 1 pennyweight of 16 carat gold to 18 carats. " The numbers representing the proportions of alloy in this example are found by respectively subtracting 18 and 16 from 24. The statement is, therefore— 6 : 8 : : 1 : li, from which it follows that to reduce one pennyweight of 16 ALLOYS OF GOLD FOR DENTAL PURPOSES. 99 carat gold to 18 carats, there must be one-third of a penny- weight of pure gold added to it. " But suppose that, instead of pure gold, we wish to effect the change by adding 22 carat gold. The numbers, then, respect- ively representing the proportions of the alloy would be found by subtracting, in the above example, 16 and 18 from 22, and the statement would be— 4 : 6 : : 1 : 1J. " It follows, then, that to each pennyweight of 16 carat gold, a half pennyweight of 22 carat gold must be added to bring it to 18 carats. " By the above rules we think the student will be able, in all cases, to calculate the fineness or quality of his gold, and to effect any reduction, whether ascending or descending, which he may desire." To facilitate the student in accurately compounding gold alloys from coins of that metal, the following table, giving the weight in grains, fineness, and the value of the gold coins of different nations, is given in this connection. TABLE OF COINAGE OF DIFFERENT NATIONS. ARGENTINE REPUBLIC. Doubloon, Province of Rio de la Plata........ Doubloon, Province of Rio de la Plata........ The same variation of fineness and weight in coins of the same date are to be found in the silver coin age of this republic. AUSTRIA. Ducat of Maria Theresa........................... Sovereign of Maria Theresa........................ Ducat of Leopold II................................ Ducat of Francis I................................. Quadruple of Francis I............................ Sovereign of Francis I............................. Sovereign of Ferdinand I........................... Half-sovereign of Ferdinand I..................... Ducat of Ferdinand I............................... Quadruple of Ferdinand I......................... Hungary ducat of Ferdinand I..................... BADEN. Ten guilder (five guilder same quality) of Louis, Grand Duke...................................... BAVARIA. Ducat of Maximilian Joseph and Charles Theodore Ducat of Maximilian Joseph II.................... Ducat of Louis..................................... Year. Weight. Fineness. Grains. Thous. 1828-32 418 815 1813-32 415 868 1762 53.5 965 1778 170 917 1790 53.5 986 1809-34 53.7 983 1830 215.5 983 1831 174.5 898 1838 174.5 901 1839 87 902 1838 53.7 985 1840 215.5 985 1839 53.7 986 1819 105.5 900 1764-97 53 980 1800 53 984 1832 53.5 987 Value. d. c. m. 14 66 15 51 2 26 6 71 2 27 74 8 77 1 38 27 8 14 28 1 100 MECHANICAL DENTISTRY. TABLE OF COINAGE OF DIFFERENT NATIONS (continued). Forty francs........................................ Twenty francs in proportion, same fineness. Sov- ereigns same as Austrian coinage. BOLIVIA. Doubloon..... ..................................... BRAZIL. Moidore of Maria I and John III................... Half-Joe of Peter II................................ The other moidores and half-Joes are of the same fineness with the moidore of 1779, varying slightly in weight. BRITAIN. The gold coins of this kingdom are of the uniform fineness of 915.5, but below the legal standard about one thousandth. The par value of the pound sterling is about $4.84. Sterling gold is worth 94.6 cents per pennyweight. BRUNSWICK. X. Thaler of Charles........................... X. Thaler of Charles WilHam Ferdinand___ X. Thaler of Wm. Fred, and George Regent. X. Thaler of Charles........................ X. Thaler of William........................ V. Thaler of Charles........................ Year. Weight. Fineness. Value 1827-36 1779 1833-38 Doubloons. CENTRAL AMERICA. Doubloons. Doubloons. COLOMBIA. Doubloon of eight escudos, Colombia, Bogotan Mint. Doubloon of eight escudos, Popayan Mint.......... Doubloon of New Granada, Bogota................. Half-doubloon of Ecuador, Quito................... Quarter-doubloon of Colombia, Bogota............. Quarter-doubloon of Ecuador, Quito................ Eighth-doubloon of Colombia, Bogota.............. Eighth-doubloon of Colombia, Popayan............ These last coins vary in fineness from 849 to 854, and in weight from 44J^ to 61^. The sixteenth-doub- loons are of the same quality. DENMARK. Specie ducat of Frederick V........................ Specie ducat of Christian VII...................... Current ducat of Christian VII.................... Christian d'or of Christian VII.................... Double Frederick d'or of Frederick VI............. EGYPT. Sequin fundoukli of Ach met III........ Sequin fundoukli of Mah moud I....... Sequin fundoukli of Mahmoud I....... Sequin fundoukli of Mustapha III..... Sequin fundoukli of Abdul Hamed..... Sequin fundoukli of Abdul Hamed..... Sequin fundoukli of Selim III.......... Half-sequin fundoukli of Mahmoud II. 1745 1805 1813-19 1824-30 1831-38 1748-64 1824-33 1819-24 1835 &seq 1823-36 1823-36 1837 1836 1823-35 1835 1823-36 1749 1795-1802 1783 1775 1813-39 1115(1703) 1143(1730) 1143(1730; 1171(1757) 1187(1773) 1187(1773) 1203 (1789) 1233(1818) Grains 199 416.5 125.5 221.5 202 204 204.5 205 205 102 417 417 417 416 8 416.5 416 8 209 104 104 51 51 53.5 53.7 48 103 204.5 Thous. 895 870 914 915 896 896 894 903 833 867 872 870 858 870 844 865 844 865 852 988 979 876 905 895 958 940 848 781 786 643 690 670 d. c. m. 7 67 15 58 4 94 8 72 7 7 81 7 87 7 89 7 91 7 89 3 96 14 96 15 57 15 66 15 61 15 39 15 61 2 13 1 57 1 42 1 31 1 32 1 08 1 15 51 1 90 1 87 1 2 27 6 2 26 4 1 81 1 4 01 4 7 88 2 ALLOYS OF GOLD FOR DENTAL PURPOSES. TABLE OF COINAGE OF DIFFERENT NATIONS (continued). 101 EGYPT (continued). Bedidlik. 100 piastres, of Abdul Majeed ........... Nusflix 50 piastres, of Abdul Majeed.............. Kairia Hastreen, 10 piastres, of Abdul Maieed..... The first date given above is the year of the Hegira the second, the Christian era. FRANCE. Louis d'or of Louis XV............................ Louis d'or of Louis XVI........................... Double Louis d'or of Louis XV.................... Double Louis d'or of Louis XVI................... Napoleon, 20 francs, of Napoleon.................. The subsequent gold coinage of France is of the uniform fineness of 899, except the twenty franc pieces of Louis Philippe, coined in 1840-41, which are 900. GREECE. Twenty drachms of Otho........................ HANOVER. Ducat of George III............................... Pistole or five thaler of George III............... Pistole or five thaler of George III............... Ten thaler of George III........................ Ten thaler of William IV and Ernst August..... HESSE. Ten thaler of Frederick II...................... Five thaler of Frederick II...................... Five thaler of William IX....................... Five thaler of William I........................ HINDOSTAN. Mohur of Bengal................................ Mohur of Bengal............................... Mohur of Bengal................................ Mohur of Bengal................................ Mohur of Madras................................ Mohur of Bombay............................... Half-mohur of Bengal........................... Star pagoda of Madras........................... Pondicherry pagoda of Pondicherry............. Porto Novo pagoda of Portuguese Company..... MECKLENBURG SCHWERIN. Ten thaler of Frederick Francis................ MEXICO. Doubloon of Mexico, Augustin, Emperor........ Doubloon of Mexico, Mexican Republic......... Other doubloons minted at Mexico weigh 417 grains, and are from 867 to 869 thousandths fine. The doubloon of Guanaxuato varies from 860 to 867 in fineness. Doubloon of Durango..... Doubloon of Durango..... Doubloon of Durango..... Doubloon of Guadalaxara. MILAN. Zecchino, or Sequin, of Maria Theresa and Joseph II Doppia, or pistole, of Joseph II..................... Forty lire of Napoleon.............................. Sovereign of Francis I.............................. Sovereign of Ferdinand I........................... Half-sovereign..................................... Year. Weight. 1255(1839) 1255(1839) 1255(1839) Grains. 132.2 66.1 27 1726-73 1786-92 1744 1786-92 1803-14 124 116.5 250 235 99.2 1833 89 1776 1803 1813-14 1813-14 1835 Aseq. 53.5 102 102 204.5 205 1773-85 1771-84 1788-89 1815-17 202 101 101.5 101.5 1770 1787 1793 1818 1818 1818 1787 190 191 191 204.7 180 179 95 52.5 52.5 52.5 1831 204.5 1822 1824-30 416.5 416.5 1833-36 417 417 417.5 416 1770-84 1783 1805-14 1831 1838 1839 53.5 97.5 199 174.5 174.5 87 Thous. 874 875 874 897 900 902 901 899 993 896 890 890 895 890 893 892 894 982 989 993 917 917 920 984 800 708 740 864 865 865 872 865 990 908 899 898 901 902 Value. c. m. 97 6 49 1 01 7 4 79 4 51 6 9 71 1 9 11 9 3 84 1 3 45 7 74 2 3 88 4 3 89 9 3 90 8 7 89 1 15 49 8 15 51 6 15 58 15 53 15 67 15 49 102 MECHANICAL DENTISTRY. TABLE OF COINAGE OF DIFFERENT NATIONS (continued). NAPLES AND SICILY. Six ducat, of Ferdinand IV.......... Onzia of Sicily of Charles........... Onzia of Ferdinand I................. Twenty lire of Joachim Napoleon... NETHERLANDS. Ducat............................ Ducat of William I............... Ten guilders of William I........ PERSIA. Toman of Fatha Ali Shah, Kajar......... Toman of Mohammed Shah, Shakinshah. Half-toman of Mohammed Shah.......... POLAND. Ducat of Stanislaus Augustus. PORTUGAL. Moidore of Peter II.............. Moidore of Peter II.............. Moidore of John V............... Half-joe.......................... Half-joe of Maria I and Peter III. Half-joe of Maria I................ Half-joe of John VI.............. Joannese of John V.............. Crown of Maria II............... PRUSSIA. Frederick d'or of Frederick II............... Frederick d'or of Frederick William II....... Frederick d'or of Frederick Wilhelm III--- Double Frederick d'or of Fred. Wilhelm III. Double Frederick d'or of Fred. Wilhelm III.. Ducat of Frederick William II............... ROME. Sequin of Pius VI........... Doppiaof Pius VI........... Doppia of Pius VII........... Gold BCudo of Rppublic....... Ten scudi of Gregory XVI.. Year. Weight. 1783 1751 1818 1813 1770-1810 1833-39 1816-39 1230-40 (1814-24) 1255(1839) 1252(1837) 1791 1689 1705 1714-26 1727-77 1778-85 1787-1804 1822-24 1730 1838 1752-82 1795-96 1799-1812 1800-11 1831 1787 1775-83 1777- 1799 1836 Imperial of Elizabeth.............................. The gold coins of Russia, though irregular in weight, are of thesame standard fineness during the reigns of Elizabeth and Catharine II. Ducat of Paul I................................... Three roubles of Nicholas.......................... Half-imperial of Nicholas......................... SARDINIA. Pistole of Victor Amadeus, etc..................... Carlino (island) of Victor Amadeus, etc............ Marengo of Republic............................... Eighty lire......................................... Genovine of Ligurian republic (Genoa)............. SAXONY. Double August d'or of Fred. August. Ill............ Double August d'or of Fred. August. Ill............ Double Anton d'or of Anthony..................... Ducat of Anthony................................. 1798 1838 1839 Grains. 135 58 53.5 53.7 103.5 71.2 53.7 27 165 165 165 217 220 221 221 439 148 102 102 102 205 205 53.5 52.5 84 84.5 910 267.5 253 60.5 100.5 148 1773 247 1800 98 398 1798 388 1784-1817 204.5 1826 205 1830-36 205 1830 53.7 Thous, 393 959 995 900 981 899 991 965 908 928 913 914 913 914 909 912 912 901 897 901 898 903 979 996 906 901 833 900 969 917 917 905 890 896 900 979 Value. c. in. 19 2 51 6 48 5 84 8 25 8 26 9 00 7 3 04 2 23 8 65 8 69 8 65 17 24 5 81 2 25 3 27 3 27 32 64 10 36 2 26 6 45 2 59 4 48 8 62 95 8 94 95 8 92 3 97 2 25 6 2 75 4 2 38 9 3 96 9 5 76 8 9 46 7 3 79 15 39 2 15 17 2 7 89 1 7 92 8 7 94 6 2 26 4 ALLOYS OF GOLD FOR DENTAL PURPOSES. 103 TABLE OF COINAGE OF DIFFERENT NATIONS (continued). SPAIN. Cob doubloon of Philip V, American.............. Doubloon of Ferdinand VI, American.............. Doubloon of Charles III, American................ Doubloon of Charles III, Spanish.................. Doubloon of Charles IV and Ferdinand VII, Ameri can.............................................. Pistole of Philip V, Spanish....................... Pistole of Charles III, American.................. Pistole of Ferdinand VII, American.............. Escudo of Charles III, Spanish.................... Escudo of Charles IV............................. Escudo of Ferdinand VII, American................ Half-doubloon of Charles III, Spanish............. Half-doubloon of Charles IV, American.......... Half-doubloon of Ferdinand VII, Spanish......... SWEDEN. Ducat of Gustavus III and Gustavus IV........... Ducat of Charles John XIV....................... SWITZERLAND. Pistole of Berne................................... Pistole of Basle.................................... Pistole of Soleure.................................. Pistole of Helvetian Republic.................... Ducat of Berne.................................... Ducat of Basle..................................... TUNIS. Half-sequin of Abdul Hamed...................... TURKEY. Sequin fondouk of Selim III...................... Sequin zermahboub of Selim III.......•........... Ohikilik of Mahmoud II.......................... Twenty piastres, of Mahmoud II.................., Yirmilik, 20 piastres, of Abdul Medjid............. TUSCANY. Ruspone of Francis III to Leopold III............ Ruspone of Louis I and Charles I.................. Ruspone of Leopold II............................ Sequin of Leopold................................ Sequin of Leopold II....... ..................... UNITED STATES. Ragle.............................................. Eagle............................................. Eagle.............................................. WURTEMBERG. Ducat of Charles.................................. Year. Weight. Grains. 1733-44 416 1751 416 1772-84 416 1786-88 416 1789-1821 416.5 1745 103 1774-82 103 1813-24 104 1786-88 52 1789-1803 52 1809-20 52 1780-82 206 1789-1808 208 1810-24 208 1777-1800 53 1838 54 1796 116 1795 118 1798 116 1«00 116 1794 52.5 53 1773 19 1789 52.5 1789 36 1822-24 25 1827 27.5 1840 24.5 1738-1800 160 1801-07 161 1824-34 161 1765-79 53 1824-34 53.5 1792-1834 270 1834-37 258 1837&seq. 258 1790-1818 53 Thous. 895* 908 843f 909 895 872 874 868 851 896 870 865 977 975 901 891 898 897 974 943 800 800 833 875 832 997 998 999 997 999 916.7 899.2 900 980 * Varies from 893 to i f Varies from 883 to 893, the oldest pieces being the best. CHAPTER VI. METHOD OF CONVERTING GOLD ALLOYS INTO THE REQUIRED FORMS FOR DENTAL PURPOSES. Manner of Procuring an Ingot.—The gold, to be molded in the form of ingot, is put into a clean crucible lined on the inside with borax, and placed in the furnace. When the contained metals are perfectly fused, the crucible should be removed from the fire with a pair of tongs, and the contents poured quickly but carefully into the ingot molds; the latter being placed conveniently near the mouth of the furnace, as the molten FlG. 52. metals soon become chilled on exposure to the open air. Before pouring, the molds, if made of iron, should be moderately heated and oiled, or coated with lamp smoke by holding their inner surfaces over the flame of an oil lamp or gas jet. Ingot molds are constructed of various substances, but those in most common use are formed of iron, and, for gold, are generally about two inches square and from one-eighth to one- sixth of an inch thick. (Fig. 52.) They should be slightly concave on their inner surfaces, to compensate for the greater shrinkage of the gold in the centre than at the margins of the ingot. Soapstone is sometimes employed for the same purpose, and 104 FORMING GOLD ALLOYS FOR DENTAL USE. 105 is preferred by some. Molds made from this substance should also be warmed and piled before pouring the metals. Molds are also made from charcoal, which is highly recom- mended for the purpose, though it requires to be frequently renewed. Prof. Gorgas, in commenting on the relative fitness or value of the several substances mentioned, says: " Iron is perhaps the most convenient; soapstone gives, with the same gold, a tougher ingot; whilst with charcoal, the greatest tough- ness of metal is obtained, so far as the nature of the ingot mold can modify it. Pig-iron, from the same furnace, run into iron molds, may be white and brittle; or into sand molds, gray and less brittle; or into charcoal, dark gray and soft. Some such molecular arrangement of gold, due to its manner of cooling, is ] >robably the correct explanation of the fact that a charcoal mold yields, other things being equal, a tougher ingot than iron." A charcoal ingot mold may be very easily and quickly made as follows: Selecting a close-grained, compact piece, of suitable size, cut through it with a saw, and then rub the divided sur- faces together until perfect coaptation is secured. The required size and shape of the mold is then cut out in one section of the block; or a strip of sheet iron, a little broader than the required thickness of the ingot, being bent into proper form, is placed between the two pieces, with the edges partially imbedded, and the whole secured in place by binding with wire, or with the use of clamps. Comparatively inexpensive, and at the same time more con- venient and durable contrivances designed ,for the same pur- pose, combining both crucible and mold, and embracing the 'special advantages claimed for charcoal, may be obtained at the dental depots. One of the simplest forms of this kind is the asbestos melting and ingot block shown in Fig. 53. When in use, place a piece of charcoal over the bowl-shaped portion of the ingot block, as it facilitates heating the metal. The small asbestos slab being placed in position to complete the mold, and retained in place by clamping, the metal, when sufficiently fused, is poured into the mold by tipping the block. The bowl or crucible lias a thin coating of whiting, to prevent borax or 106 MECHANICAL DENTISTRY. other flux from adhering. Should this occur, however, rub a little moist whiting in the bowl. The sides of the block are encased in strips of wood, to protect the hands from heat. A very ingenious, convenient, and useful apparatus, com- bining crucible and ingot mold, by the use of which ingots of Fig. 53. gold, silver, etc., may be quickly obtained without the use of a furnace, is shown in Fig. 54. The crucible is of molded carbon, and is supported in position by an iron side plate. A clamp holds crucible and ingot mold in position, swiveling on a cast-iron stand. The metal to be melted is placed in the crucible, and the Fig. 54. flame of the blowpipe directed on it until it is perfectly fused. The waste heat serves to make the ingot mold hot, and the whole is tilted over by means of the upright handle at the back of the mold. With this simple instrument, a sound ingot may be obtained at any time in about two minutes. FORMING GOLD ALLOYS FOR DENTAL USE. 107 Aside from the greater convenience and cleanliness, as com- pared with the older method in which draught-furnace heat is used, there is great economy of time in the use of the last named appliance combining crucible and mold, since an ingot may be thus obtained, with the use of the bellows or hydrostatic blow- pipe, in from two to three minutes. They are suitable for melting from two to four ounces of gold or silver. It not unfrequently happens that, at the first pouring, the metals arrange themselves in the ingot in accordance with the density of the several components, those of greater specific gravity passing to the bottom, and the lighter metals remaining above. Whenever this occurs, the ingot must be broken into pieces and remelted; this should be repeated, if necessary, until Fig. 55. Fig. 56. the alloy assumes a perfectly homogeneous appearance. It should then be annealed in hot ashes, which softens the gold and removes the adhering grease. Forging.—Before laminating the ingot it should be reduced somewhat in thickness by placing it on an even-faced anvil or other equally smooth and resistant surface, and subjected to repeated blows with a tolerably heavy hammer. It should be frequently annealed, and the process of forging continued, alternately hammering and annealing, until the ingot is re- duced one-half or more in thickness. Laminating or Rolling—The reduced ingot, well annealed, is next laminated or spread out into a sheet of greater or less ' 108 MECHANICAL DENTISTRY. thinness by passing it repeatedly between two strong, highly- polished, cylindrical steel rollers. The mills used for the pur- pose are variously constructed, the plainest forms (Fig. 55) being very simple in their mechanism, while others, or geared mills, are more complicated, and are constructed with a view to a greater augmentation of power, and precision, and certainty of action. The latter (Figs. 56, 57), if of approved pattern, materials, and manufacture, are, upon the whole, more economi- FlG. 57. cal and reliable than the cheaper varieties. The rollers, for the purposes of the dentist, should be from three to four inches in length. In laminating, the rollers should first be adjusted equidistant at both ends, and this uniformity, as they are approximated from time to time, should be preserved throughout. At every passage of the gold bar between the rollers the distance be- FORMING GOLD ALLOYS FOR DENTAL USE. 109 tween the latter should be diminished, care being taken that the approximation be not sufficient to clog or impede the free action of the mills. The gold, which, in time, becomes hard, and brittle, and liable to crack in the mills, should be frequently and well annealed by bringing it to a full red heat; this re- stores the pliancy of the gold and facilitates the operation in the press. When the ingot has been extended in one direction as far as may be desired, it should always be re-annealed before turning it in the mills; a neglect of this precaution will seriously inter- fere with the working of the gold by twisting or doubling the plate upon itself; and in some instances, provided the gold Fig. 58. has not been well annealed throughout the operation, or is in any considerable degree unmalleable, the plate will be torn across and rendered unfit for use. A thin or retreating edge may be given to the plate at any desired point or points by passing such portions part way between the rollers and withdrawing; repeating this, with the rollers brought a little nearer to each other every time the plate is introduced between them, and decreasing the distance the plate passes each time until it is reduced to as thin an edge as may be desired. The degree of attenuation obtained by rolling is determined 110 MECHANICAL DENTISTRY. by what is called a gauge plate (Fig. 58). This instrument is usually circular or oblong in form, and is marked at intervals on its edge by cross-cut grooves or fissures, which successively diminish in size and are indexed by numbers ranging from 6 to 40. The size of the grooves diminish with the ascending numbers. During the operation of rolling, the plate should be tested, from time to time, by the gauge, to determine when it has undergone sufficient attenuation. Thickness of Gold Plate required as a Base for Artificial Den- tures.—In prescribing the thickness of plate proper for the purpose indicated, no estimate can be given that will apply to all cases, as certain conditions of the mouth, to be mentioned hereafter, will suggest some modifications in this respect. Usually, however, plate for entire upper sets should correspond in thickness with number 26 of the gauge plate; for the under jaw, number 24 may be used; while for partial upper pieces, an intermediate number may be chosen, unless atmospheric- pressure plates are used, when the number recommended for full upper sets may be employed. Thickness of Plate for Clasps, Stays, etc.—Plate for these pur- poses should correspond with from 20 to 22 of the gauge; a less amount of substance, as before stated, being required when the alloy has incorporated with it a small proportion of platinum. Reduction of Gold Solders into Proper Form for Use.—The method of converting gold solders into the form of plate does not differ from that already described in the manufacture of plate as a base, except that when zinc or brass is used, the latter should be added after the other constituents are com- pletely fused, and then instantly poured, to prevent undue wasting of the base metals by a too protracted heat. The solder should be reduced to plate somewhat thinner than that used for upper sets, 28 of the gauge plate. It is customary sometimes to roll the solder into very thin ribbons, but this is objectionable for the reason that a greater amount of the alloy- ing metals being exposed in a given surface to the action of the heat in soldering, are burnt out or oxidated, which interrupts the flow and weakens the attachment between the solder and plate. Method of Obtaining Gold Wire.—To convert gold or its alloys FORMING GOLD ALLOYS FOR DENTAL USE. Ill into the form of wire, the operator should be provided with a draw plate, a vise, and a pair of hand pincers. A draw plate (Fig. 50) is an oblong piece of steel pierced with a regular gra- dation of holes, or a series of progressively diminishing aper- tures, through which the gold bar, reduced to a rod, is forced and made to assume the form and dimensions of the hole through which it is last drawn. The holes are formed with a steel punch, and are enlarged on the side where the wire enters and diminish with a gradual taper to the other side. A draw bench is sometimes employed in extending the wire, the power being applied by a toothed wheel, pinion, and rack-work, and is moved by the hands of one or two persons. For the pur- Fig. 59. poses of the dentist, however, it will be sufficient to fix the draw plate securely between the jaws of a bench vise, and, by seizing hold of one end of the gold rod with a strong pair of clamps or hand pincers, serrated or cut like a file on the inside of the jaws, the wire may be drawn steadily through the plate, passing from the larger to the smaller holes until a wire of the required size is obtained. In drawing the wire, the motion should be steady and uniform, for if drawn interruptedly or by jerks, the wire will be marked by corresponding inequalities. The gold rod should also be annealed from time to time, and the holes kept well greased or waxed. 112 MECHANICAL DENTISTRY. The process described above will answer equally well in reducing any of the ductile metals to wire, as silver, copper, platinum, etc., so that any further description of the method, in connection with these metals, will be unnecessary. Method of Constructing Spiral Springs.—Inasmuch as spiral springs have been, to a great extent, superseded by more ap- proved agencies employed in the retention of artificial teeth in the mouth, and as all the principal dental furnishing houses are supplied with these appliances already prepared for use, the author does not deem it necessary to enter into a descrip- tion of the various apparatuses used in making them. Fig. 60. The following simple contrivance will meet the limited re- quirements of those who are obliged or prefer to manufacture their own springs. The wire, obtained as already described, is held between two blocks of wood fastened between the jaws of a bench vise, as shown in Fig. 60. By means of a small hand vise, one end of the wire is clamped to a uniformly cylindrical and well-tempered steel rod or wire, four or six inches long, and about the size of a small knitting-needle, and which being made to revolve while resting on the blocks of wood, the wire is wound firmly and compactly around it, producing a uniform coil. CHAPTER VII. SILVER. General Properties of Silver.—Pure silver, when planished, is the brightest of the metals. Fused, or in the form of ingot, its specific gravity is 10.47; but when hammered or condensed in the coining press, its density is increased, and its specific gravity becomes 10.0. It fuses at an extreme red heat, generally esti- mated at 1.873° Fahrenheit. It is remarkably laminable and ductile; yielding leaves not more than TTnnnro" of an inch thick, and wire 400 feet of which may be drawn weighing but a single grain. It exceeds gold in tenacity or cohesion, but is inferior to platinum in this respect, A silver Mre .078 of an inch in diameter will sustain a weight of 187.13 pounds. Fine silver is unaffected by moisture or pure atmospheric air, but is readily tarnished with a film of brown sulphuret by exposure to sul- phuretted hydrogen. The sulphuret of silver thus formed may be easily removed by rubbing the metal with a solution of chameleon mineral, prepared by calcining equal parts of black or peroxide of manganese and nitre. Unlike gold and platinum, it is readily soluble in nitric acid; this and sulphuric acid being the only simple ones that dissolve it. Silver becomes very brilliant when heated; boils and vaporizes above its fusing point; and when cooled slowly, its surface presents a crystalline appearance. Alloys of Silver.—Silver combines readily with most metals, forming compounds of variable degrees of malleability, duc- tility, density, etc. Tin, zinc, antimony, lead, bismuth and arsenic render it brittle. A very minute quantity of tin is fatal to the ductility of silver. Silver does not easily combine with iron, although the two metals may be united by fusion. Gold, copper, platinum, iridium, steel, manganese, and mercury, also form alloys with silver. An alloy of nine parts of silver and one of copper is the 8 113 114 MECHANICAL DENTISTRY. Government standard of the United States coinage since 1837. To this, three-cent pieces form an exception; these being com- posed of three parts silver and two of copper. The coins of silver having a greater average fineness than those of our own country, are Brazil, Britain, Chili, France, Greece, Hindostan, Persia, Portugal, Rome, and Tuscany. A common impression prevails that the Mexican silver coin contains more than an average percentage of pure silver, and it is therefore sought after, on account of its supposed purity. This is true of some pieces coined at different periods, but the average fineness of the Mexican, as well as Spanish coins, falls below that of the United States mints. Refining Alloys of Silver.—The following account of the man- ner of obtaining pure, or nearly pure, silver from alloys of that metal by the dry (roasting) and wet (humid) methods, are given by Prof. Essig, in'his treatise on " Dental Metallurgy":— Dry Method.—" The dry method or assaying process consists in forming an alloy of the silver with lead, and is especially applicable to ores and the sweepings of the dentist's laboratory. The specimen to be treated is heated with from twelve to thirty times its weight of granulated lead, in a bone-ash cupel, which is placed in a muffle so arranged that a current of atmospheric air may pass freely over the vessel and oxidize the lead. This oxide of lead, being quite fusible, combines with any base metal present and oxidizes it, uniting subsequently with the oxide as a fusible slag, while the gold or silver will be held by the unoxidized portion of the lead. In the treatment of speci- mens of alloys, such as plate or coins, a quantity of the specimen is accurately weighed and mixed with from four to five times its weight of pure granulated lead. It is then placed in the cupel and exposed to heat, as above described, until all the lead is oxidized or converted into litharge, when the remaining button assumes the brilliant appearance of surface before alluded to, which denotes that the base metals or oxidizable constituents have been oxidized and taken up by the lead oxide. This button is then to be weighed by means of a delicate assay balance, and the loss of weight denotes the amount of alloy that was present. SILVER. 115 Wet Method.—" Pure silver, which is reckoned as 1000 fine, may be obtained from standard or other grades of silver by dissolv- ing them in nitric acid slightly diluted with water, the solution being much facilitated by exposure to gentle heat. If gold be associated with the alloy it will be found at the bottom of the vessel, in which case it will be necessary to use a siphon to remove the argentic nitrate solution. The silver is now to be precipitated in the form of chloride by the addition of an excess of common salt. When all has subsided the liquid is carefully poured off, and the chloride thoroughly washed, to remove all traces of acid. The chloride is then placed in water acidulated with hydrochloric acid (an ounce of chloride requiring six to eight ounces of water) and pieces of clean wrought-iron put in it, when a copious evolution of hydrogen follows, which, uniting with the chlorine of the argentic chloride, liberates metallic silver. The latter should not be disturbed until the last particle of it is thus reduced, when it will be found to be a spongy mass. The undissolved iron should now be carefully removed, the ferrous and ferric chloride carefully decanted, and the silver washed in hot water containing about one-tenth its bulk of hydrochloric acid. This is repeated several times, and finally the silver is again thoroughly washed with pure hot water. The silver, after drying, is then ready for melting, and if care has been observed in the process it will be found to be of a fineness of 000.7 parts in 1000, the 0.3 of impurity present being due to traces of iron. The chlorides may be acidulated with sulphuric acid, and reduced with zinc instead of iron. "Another method of precipitating silver in the metallic form consists in placing a sheet of copper in a solution of argentic nitrate. The metal is thrown down in a crystalline form. Silver thus obtained is never free from traces of copper. " Pure silver can only be obtained from samples of a lower grade by fusing the pure chloride with sodic carbonate. The reaction is shown in the following equation:— 2AgCl + Na2C03 = Ag2 + 2NaCl + O + C02. Owing to the copious evolution of carbonic acid gas which takes place during the decomposition, some of the silver may be thrown from the crucible, and loss may occur by the absorp- 116 MECHANICAL DENTISTRY. tion by the crucible of some of the fused chloride. To avoid this, the sides of the vessel should be coated with a hot satu- rated solution of borax. " A composition of 100 parts of argentic chloride, 70.4 of calcic carbonate (chalk), and 4.2 of charcoal, has been recommended as a means of obtaining pure silver. This mixture is heated to dull redness for thirty minutes, and then raised to full red- ness ; carbonic acid and carbonic oxide are given off; the calcic chloride is converted into calcic oxy chloride, underneath which, in the bottom of the crucible, will be found the button of pure silver." Reduction of Silver to the Required Forms for Dental Purposes.— Owing to the very soft and flexible nature of silver in its pure state, it is usual, when converting it into plate or other forms for use, to employ an alloy of the metal. Hence silver coins, which are made harder by the copper they contain, are gener- ally selected for the purpose. The employment of silver, thus debased, as a base for dental substitutes is regarded by many as unsafe and injudicious. Although the influences of an alloy so readily acted upon as this by the various agents which affect it chemically cannot always be certainly predicted in every case, yet no reasonable doubt can be entertained but that, under the favoring conditions which usually exist in the mouth, the evils accruing, directly and indirectly, to the organs of the mouth, and through them to the general system, are positive and undoubted. If used at all, therefore, it should be alloyed with the least practicable amount of copper, or, what is better, pure silver should be reduced with platinum alone, in suffi- cient quantities to impart to the plate an adequate degree of strength and elasticity. The tendency of silver to tarnish in the mouth when alloyed with copper may be diminished by boiling the finished piece in a solution of cream of tartar and chloride of soda, or common salt, or by scrubbing it with aqua ammonia, which removes the superficial particles of copper, and exposes a surface of fine silver. When platinum is introduced as the sole alloying component, the purity of the silver is not only preserved, but the alloy is less easily acted on chemically, while the plate derived from it is rendered sufficiently inflex- SILVER. 117 ible and elastic. From three to five grains of platinum may be added to one pennyweight of pure silver. On account of the strong affinity of sulphur for silver, the fuel most proper to be used in melting it is charcoal. The various processes employed in the conversion of silver into the required forms for use are similar to those described for gold, and need not be recapitulated. Formulas for Silver Solders.—Silver solders are usually composed of silver, copper and zinc, in variable proportions. Alloys formed from the following formulas are such as are generally employed in soldering silver plate derived from the coins of that metal. Three-cent pieces, composed of two parts silver and one of copper, may also be used for the same purpose:— Formula No. 1. Formula No. 2. Silver,.....66 parts. Silver,.....6 parts. Copper, .... 30 " Copper, .... 2 " Zinc,.....10 " Brass,.....1 " When the material to be united is composed of pure silver and platinum, silver coin alloyed with one-tenth zinc may be used as a solder. In compounding silver solders, the silver and copper should be first melted, and the zinc or brass afterward added, when they should be quickly poured, to prevent undue waste, by oxidation, of the more fusible component. The ingot, when cold, should be rolled into a plate a little thicker than that recommended for gold solder. CHAPTER VIII. PLATINUM AND THE PLATINOID METALS. Platinum is, a grayish-white metal, resembling, in, some measure, polished steel. It is harder than silver, and has a density greater than any other known metal, its specific gravity being 21.25. It remains unaltered in the highest heat of a smith's forge, and can only be fused by means of the oxy- hydrogen blowpipe and galvanism. A white heat does not tarnish it, nor is it in any way affected by exposure, either in the air or water. It is insoluble in any of the simple acids; nitro-muriatic acid being the only one that dissolves it. It is sufficiently malleable to be hammered into leaves so thin as to be blown about by the breath. It may be drawn into wire the two- thousandth of an inch in diameter, and a still greater attenua- tion may be obtained by coating the wire with silver, drawing it out, and dissolving off the latter metal. It expands less by heat than any other metal, and is much inferior to gold, silver and copper as a conductor of electricity. While it does not oxidize in the air at any temperature, nor is soluble in any one acid, if heated to redness in the air in contact with caustic alkalies or alkaline earths, a hydrated oxide is formed which combines with the alkaline base, in a similar manner to palladium. Platinum is very soft and flexible, and when rolled into thin sheets, say 28 or 30 of the gauge-plate, and well annealed at a strong white heat for eight or ten minutes, it may be readily forced into all the inequalities of a zinc die without producing any appreciable change in the face of the latter. The following interesting and practical observations on the method of melting and welding platinum scraps are by E. A. L. Roberts. By the process of welding, the operator will be enabled to re-convert his waste scraps of platinum into con- venient forms for use, and which he could not otherwise avail himself of, on account of the infusible nature of this metal in its uncombined state :— " Platinum used by dentists should be soft, tough, and with- 118 PLATINUM AND THE PLATINOID METALS. 119 out flaws. These qualities can be attained only by thorough melting and welding. The welding must be done at a white heat. When the surface is cool enough to be visible, the metal is too cool to be welded, and every blow is injurious, because it has a tendency to shatter and shake it to pieces. The necessary delicacy of this process, and the uncertainty of success, has led some writers to declare that platinum is incapable of being welded. The platinum must be perfectly clean, and must be heated in a muffle. When welded, the metal should he handled with tongs plated with platinum, and hammered with a clean hammer on a clean anvil, both of which should be as hot as possible, without drawing the temper of the steel. The ham- mer used in welding should weigh about a pound, to prevent drawing the metal; but when welded, the metal may be forged with a heavier hammer. " The scraps or sponge should be condensed in a square mold, very compactly, two pieces of which, weighing from ten to twenty ounces, may be put into a muffle together. When the heat becomes so great that on opening the door the metal becomes invisible, bring one of the pieces, in-the tongs, quickly to the anvil, give it three or four quick, sharp blows, in rapid succession. Return the piece to the muffle, and proceed with the other piece in like manner, and thus alternately till both are thoroughly welded. " Platinum should never be thrown into water while hot, as that tends to make it crystallize. It should be thoroughly hammered, which makes it tough and fibrous. " The following process gives the best results in melting this metal. Condense the scraps, sponge, -or filings in an iron mold. Lay the condensed mass on a concave fire-brick, and heat it to whiteness. Take the brick from the muffle, and place it in a sheet-iron pan, coated with plaster and asbestos. The pan should be deep enough and broad enough to catch all globules and other loose particles of the metal. Place it under the jet of the oxyhydrogen blowpipe, in the following manner:— " The pan is provided with a handle, opposite to which is a ring, which is to be attached to an iron hook and rod, suspended from the ceiling by a slip of india-rubber, which enables the 120 MECHANICAL DENTISTRY. operator to hold the pan conveniently at any distance from the jet of the burning gases. The hydrogen is first lighted, and gives a powerful flame, but as the oxygen combines with it, the flame subsides into an intense focus of heat, in which the metal is soon brought to a state of fusion. Begin at one end and melt along toward the other, till the whole is fused in one mass. The platinum in this condition, when cool, is quite crystallized and sonorous. It breaks very easily, like spelter-zinc. Heat it very hot and forge it. A continuation of this process renders it soft, tough, and fibrous. When reduced to the width desired, and to the thickness of one-fourth of an inch, it should be made very hot, and passed instantly through the rollers." Platinum, in mechanical practice, is chiefty employed as a base for continuous-gum work; it is also used as a coloring ingredient of porcelain, and for pins for attaching mineral teeth; and, to a limited extent, in some of the minor operations of the shop. Pure gold is the only proper solder for this metal. Alloys of Platinum.—Platinum unites with most of the base metals, forming alloys of variable degrees of hardness, elas- ticity, brittleness, color, fusibility, etc., but their practical value to the dentist is not sufficient to justify a separate description of their properties. Alloyed with gold it forms a straw-colored alloy, the shade depending on the quantity of gold added. Silver hardens it, the resulting alloy being unaffected by sulphur. Platinoid Metals.—The platinoid metals, palladium, iridium, osmium, rhodium, and ruthenium, are native contaminations, the alloys of these metals having a close general resemblance to platinum. Among the platinoid metals, palladium and iridium are the only ones that have been used for dental purposes, and these only to a limited extent. Palladium is of a steel-gray color, and when planished, is a brilliant steel-white metal, not liable to tarnish in the air. Though closely resembling platinum, it may be readily distinguished from the latter metal by the follow- ing tests: 1. It has little more than one-half the density of platinum. 2. If a piece of it is heated to redness, it assumes a bronze-blue shade, of greater or less intensity, as it is cooled PLATINUM AND THE PLATINOID METALS. 121 more or less slowly ; but if it is suddenly chilled by immersing it in cold water, it instantly resumes its original lustre. 3. When a drop of the tincture of iodine is let fall upon its surface and evaporated over the flame of a lamp, a black spot remains, which does not occur with platinum. Palladium melts at about the heat required to fuse malleable iron, and is the most fusible of the platinoid metals. It is soluble in nitric acid, but its best solvent is nitro-hydrochloric acid. Palladium, being very costly, and possessing no properties that specially recommend it for dental uses, is but little employed in prosthetic practice. Iridium, though generally found associated with platinum, osmium, and other allied metals, sometimes occurs native and nearly pure. Like platinum, it is very refractory when exposed to high temperatures, and can only be fused by the oxyhydro- gen blowpipe, or by the heat of the voltaic current. An alloy of one-fifth platinum and four-fifths iridium has been met with in octahedral crystals, whiter than platinum, and of specific gravity 22.00. When native platinum is dissolved in nitro- hydrochloric acid, black scales remain behind, which are com- posed of iridium and osmium. These metals may then be separated by one of the methods in use, and the iridium is obtained in a gray metallic powder, resembling spongy plati- num. Iridium is very hard, white and brittle, and has a specific gravity of 21.15. None of the acids attack the pure metal, but when alloyed with platinum it is readily dissolved by aqua regia or nitro-hydrochloric acid. If heated in a finely- divided state in the open air, iridium absorbs oxygen; it is also oxidized by nitre and caustic potash. The extreme hardness, and consequent rigidity, of iridium renders it, in its unalloye'd state, practically unfit for base plates, on account of the great difficulty of swaging it into proper form. This, however, may be accomplished in certain cases, as in partial pieces, with the use of zinc dies and counters; and in these cases it is desirable on account of the increased strength its property of hardness imparts to the plate. It may be used to advantage, however, alloyed with platinum, a small quantity imparting to the latter increased stiffness and elasticity. CHAPTER IX. ALUMINUM. Aluminum is the metallic basis of alumina, the latter being the characteristic ingredient of common clay. It is only within the past few years that the attention of chemists has been directed to the production of this remarkable metal with a.view to its general introduction into commerce and the arts. Prior to the researches of M. Deville, who, under the patronage of the then Emperor of the French, commenced his researches in 1854 for the production of this metal on a large scale, the small quantities produced and the corresponding exorbitant prices it commanded, rendered it entirely unavailable for other pur- poses than merely scientific experiment. The improvements in the methods of obtaining it, however, which have been more recently introduced, cannot fail to render its production more economical, and it is now supplied in much larger quantities and at a corresponding reduction in the cost of the metal:— The following account of the properties of this metal is taken from a paper read before the Society of Arts, London, by its Secretary, P. Le Neve Foster. It embodies a very com- plete description of the properties of this remarkable metal:— " One of the most striking properties of aluminum is its extreme lightness, its specific gravity being 2.6, nearly that of glass, whilst that of platinum is 21.5, gold 19.5, silver 10.5, copper 8.96, zinc 7.2, tin 7.3. "The metal is malleable, ductile, almost without limit; it can be reduced to very thin sheets, Or drawn into very fine threads. Its tenacity, though superior to that of silver, is less than that of copper; but no very accurate experiments have been made in this respect. " When pure it is about as hard as silver. Its elasticity is not great. It files readily, and is said not to injure the file. It conducts electricity with great facility, so that it may be con- sidered as one of the best conductors known, almost equal in 122 ALUMINUM. 123 this respect to silver, and more than eight times a better con- ductor than iron. It melts at a temperature a little above that of zinc, between zinc and silver. In its chemical qualities it would seem to take an intermediate rank between what are termed the noble metals and the common metals, being, as Deville states, one of the most unalterable of metals. " It might be imagined that it would as readily reassume its oxygen as it parted with it with difficulty when in its state of oxide. This, however, is not the case; it appears to be as in- different to oxygen as either platinum or gold. In air and in oxygen it undergoes no sensible alteration, and it even resists it at the highest temperature which Deville could produce in a cupelling furnace, a temperature higher than that employed in assaying gold. Water has no action, according to Deville, on aluminum, neither at its ordinary temperature, nor when boiling, nor even upon the metal at a low red heat, near its melting point. According to Professor Crace Calvert, this state- ment must be received with some degree of caution, as in experiments he has made he considers that oxidation does take place slowly when the metal is immersed in water for any considerable length of time. It is not affected by sulphur or sulphuretted hydrogen, like silver, nor is it acted upon to any considerable degree by any of the oxy-acids in the cold ; nitric acid, whether strong or weak, at its ordinary temperature, in no way affects it, though when boiling it acts upon it slowly. Small grains of aluminum, plunged in sulphuric acid for three months, remained apparently unaltered. The vegetable acids, such as acetic, oxalic and tartaric acids, have scarcely any effect on it at all. The true solvent of the metal is hydrochloric acid, which attacks it rapidly. It appears to resemble tin when brought into contact with hydrochloric acid and the chlorides. Its absolute harmlessness permits of its being employed in a vast number of cases where the use of tin would not be desir- able on account of the extreme facility with which that metal is dissolved in the organic acids. " Figuier, in his scientific Year Book for 1858, just published, states that the caustic alkalies, potash, and soda, and even ammonia, dissolve aluminum sensibly. He also states that 124 MECHANICAL DENTISTRY. common salt and acetic acid (vinegar), especially when mixed, attack and dissolve aluminum. He adds, that the mixture of salt and vinegar for seasoning a salad, made in a spoon of aluminum, feebly but inevitably attacks it. "All these points, however, deserve to be inquired into, as there seems some discrepancy between different writers on them." Alloys.—"Aluminum, like iron, does not unite with mercury, and scarcely at all with lead. It, however, forms a variety of alloys with other metals. It can be alloyed with iron, and when aluminum becomes cheaper, it will be curious to see what effect mixtures of this metal with iron will have upon its quality, whether for good or for evil. It seems to unite readily with zinc, and these have been found to give the best promise as solders for aluminum; but, unfortunately, when melted, neither of them are sufficiently liquid, and do not run readily. The joints will not bear a blow. A variety of alloys with nickel have been made, and that consisting of 100 parts of aluminum and 3 of nickel is found to work readily, and to have gained hardness and rigidity, as compared with the pure metal. The alloys, however, with copper are the most striking; they are light and very hard, and capable of a fine polish. In the same degree that copper adds to the hardness of aluminum, so does the latter, when used in small quantities, give hardness to copper, without, however, injuring its malleability. It renders it susceptible of a fine polish, and, according as the proportions are varied, the color of the alloy becomes deep or pale gold. Alloys of copper with five and ten per cent, of aluminum resemble gold, perhaps, more than any other metallic alloy hitherto employed. They do not tarnish sensibly by exposure to the air. Aluminum can be deposited by the battery, and by the same agent it can be gilt or silvered." Some attempts have been made to render aluminum avail- able as a base for artificial teeth, but with only partial success. When in the form of plate, no suitable solder has yet been discovered by which the several parts of a dental appliance may be securely united to each other; and experiments in casting this metal have practically failed, owing to its extreme ALUMINUM. 125 lightness and consequent want of fluidity, its great contraction, and its susceptibility to the action of alkaline solutions. More experience in its proper management, and a further acquaintance with its capabilities in yet unknown forms of combination with other metals, may ultimately demonstrate its applicability to dental purposes. At the present time, its use is rarely attempted except as a base in connection with rubber or celluloid, the latter substances being employed as a means of attaching teeth by a method similar to that described in another place when gold or silver plate is used. CHAPTER X. COPPER, ZINC, LEAD, TIN, ANTIMONY, AND BISMUTH. COPPER. Copper is one of the metals most anciently known ; it is of a brownish-red color, with a tinge of yellow; has a faint but nauseous and disagreeable taste, and imparts, when exposed to friction, a smell somewhat similar to its taste. Its specific gravity ranges from 8.8 to 8.9. It is both malleable and ductile, but excels in the former property, finer leaves being obtained from it than wire. It is inferior to iron in tenacity, but surpasses gold, silver and platinum in this respect. Copper melts at 1996° Fahrenheit. Alloys of Copper.—Copper unites readity with most metals, forming alloys of great practical value in the arts, but which have but a limited application in dental laboratory processes. Many of these alloys are curious and instructive, as illustrating the singular and unaccountable influence of alloying upon the distinctive properties of the component metals. Copper and tin, for example—the former of which is highly ductile, and the latter equal malleable—when combined in the proportion to form speculum metal (9 C : 1 T), form an alloy distinguished for its extreme brittleness, with a surface hardness almost equal to steel. By increasing the quantity of tin until the compound assumes the proportions constituting gun-metal (C 2 : T 1), the alloy, though neither malleable nor ductile, becomes eminently tough and rigid. Other prominent examples might be given, showing how completely this combining influence defies all calculations in regard to ultimate results. The following summary embraces the names and composition of the more familiar alloys of copper, omitting, as unnecessary in this con- nection, a description of their individual properties. Alloys of Copper with Zinc.—Brass is an alloy of uncertain and variable composition, consisting usually, however, of two to five parts of copper and one of zinc. Brass melts at 1869° Fahr. 126 COPPER. 127 Prince's metal, and its allied compounds, Pinchbeck, Similor, and Manheim gold, consist of nearly equal parts of copper and zinc. Mosaic gold consists of 100 parts of copper and from 52 to 55 of zinc. Dutch, gold, from which foil of that name was formerly obtained, is formed of 11 parts of copper with 2 of zinc. Bath metal is composed of 32 parts of brass and 9 of zinc. Brass solder consists of two parts of brass and one of zinc, to which a little tin is occasionally added. Alloys of Copper w-ith Tin.—Bell metal usually consists of 100 parts of copper with from 60 to 63 parts of tin. Cannon metal is compounded of 90 parts of copper with 10 of tin. Cymbals and gongs contain 100 parts of copper and 25 of tin. Speculum metal consists of two parts of copper and one of tin. Copper and arsenic form a white-colored alloy, and in the proportion of nine parts of copper and one of arsenic, is white, slightly ductile, and is denser and more fusible than copper. Genuine German silver is composed of copper, 40.4; nickel, 31.6; zinc, 25.4; iron 2.6; but the proportions of the metals of this alloy differ according to the various uses to which this compound is applied. Chinese packfong consists of five parts of copper alloyed with seven parts of nickel and seven parts of zinc. Babbitt metal is a compound of copper, antimony, and tin, in somewhat varying proportions. The following formula is given by Henry Long Jacob, in the Britisli Journal of Dental Science :— Copper...................2 parts Antimony.................3 parts Tin....................12 parts. The following method of preparing it is given by the same writer:— "In preparing this metal, the copper is first melted in a crucible, with about an equal weight of tin (the copper thus fusing much more readily than by itself); a little more of the tin is then added, next the antimony, and lastly the remainder of the tin by degrees, stirring well during the whole of the time; the metal can then be poured into sand molds of any convenient form. About a year and a half ago, I furnished Mr. T. Fletcher 128 MECHANICAL DENTISTRY. with this formula, and I believe it is given in his work on' Dental Metallurgy.' The melting point of this metal is lower than that of zinc, and somewhat higher than that of lead, so that counter-molds of this latter can be readily made to it with proper care. I am under the impression that the original Bab- bitt metal was said to contain a portion of lead, but this addition I found to be injurious." ZINC. Zinc is a bluish-white metal, possessing considerable lustre when broken across. The commercial variety is always impure, containing traces of iron, lead, cadmium arsenic, carbon, etc. It does not easily tarnish in dry air, but soon becomes dull on ex- posure to moisture. In the condition in which it ordinarily occurs it is a brittle metal, but may be rendered malleable by annealing it at certain temperatures. This change in its con- dition is effected by subjecting it to a heat of from 220° to 300° at which temperature it may be rolled into sheets, and retain its malleability when cold. The best annealing temperature for zinc is about 245°. A knowledge of this fact will enable the operator to avail himself of the advantages of this property by annealing his zinc die, by which its liability to crack or part under the hammer is diminished. The specific gravity of zinc varies from 6.9 to 7.2. It melts at about 773°, and when heated much above this point with contact of air, it burns with a brilliant greenish-white flame, while woolly-looking flocculi rise from the vessel in which it is being heated and float in the air. Zinc has been long and almost exclusively employed in the formation of dies used in swaging metallic plates employed in mounting artificial teeth, and experience has very justly accorded to it undisputed pre-eminence above all other un- alloyed metals for the purpose. A more particular account of its peculiar fitness for dental purposes will be given under the head of Metallic Dies and Counter-Dies. LEAD. Lead has a grayish-blue color, with a bright metallic lustre when melted or newly cut, but it soon becomes tarnished and TIN. 129 dull-colored when exposed to the air. The specific gravity of commercial lead, which is usually contaminated with other metals, is 11.352. It fuses at 612°. Exposed to a high heat, it absorbs oxygen rapidly, forming on its surface a gray film of protoxide and metallic lead. It is both malleable and ductile, but soft and perfectly inelastic. Lead, either in its pure state or when alloyed with certain other metals, serves important purposes in the laboratory. In its simple or uncombined state it is useful only in forming counter-dies. Alloyed with antimony in the proportion of from \ to \ of the latter, with the addition sometimes of very small portions of copper, tin, and bismuth, it forms different grades of type-metal, which is harder than lead, and very brittle, and is sometimes used for dies; and sometimes, though very rarely, for counter-dies. When used as a counter to a zinc die, it is improved for the purpose by adding to it an equal quantity of lead ; it may also be used in the form of a die in connection with a lead counter after rough stamping with zinc. The alloy known as Rose's fusible metal is composed of two parts of bismuth to one of lead, and one of tin, and melts at about 200°. A still more fusible alloy is composed of lead 3 parts, tin 2 parts, and bismuth 5 parts, which fuses at 197°. There are other alloys of lead, to be mentioned hereafter, melting at from .200° to 440°, which may be advantageously employed in forming dies to be used after zinc, where the latter, from its greater shrinkage, fails to bring the plate into accurate adapta- tion to the mouth. Soft solder is an alloy composed of lead and tin in the propor- tion of two parts of the former to one of the latter. TIN. Tin is a brilliant, silver-white metal, the lustre of which is not sensibly affected by exposure to the air, but is easily oxid- ized by heat. It has a slightly disagreeable taste, and emits, when rubbed, a peculiar odor. It is soft, inelastic, and, when bent, emits a peculiar cracking sound called the creaking of tin. It is inferior in tenacity and ductility, but is very malleable, and may be beaten into leaves the yttW of an inch in thick - 9 130 MECHANICAL DENTISTRY. ness; ordinary tin foil being about r^Vo" of an inch thick. It fuses at 442°; boils at a white heat, and burns with a blue flame to binoxide. The more common alloys of tin with other metals have already been noticed. It was at one time used as a base for artificial teeth; and more recently, it has been introduced as a component of " cheoplastic " metal, a compound used for the same purpose. In its pure state, it is sometimes used for counter-dies, and occasionally for dies. When employed for the latter purpose in connection with a lead counter, the latter should not be obtained directly from the die, as the high tem- perature of melted lead would produce, when poured upon tin, partial fusion of the latter and consequent adhesion of the two pieces. When tin is used in the formation of a die, therefore, either a counter previously obtained from a zinc die should be used, or the " dipping" method employed, by which the counter-die is first obtained from the plaster model, and a die from the counter. ANTIMONY. Antimony is of a silver-white color, with a tinge of blue, a lamellar texture, and a crystalline fracture. It is brittle and easily pulverized. The specific gravity of the purest variety is 6.715. It fuses at about 810°, and when heated at the blow- pipe, it melts with great readiness, and diffuses white vapors, possessing somewhat of a garlic smell. Antimony enters as an ingredient into the composition of type and stereotype metal, music plates, and Britannia metal. It is also a component of certain fusible alloys analogous to those already mentioned under the head of lead, and which, in the form of a die, are sometimes used on account of their slight degree of shrinkage. BISMUTH. Bismuth is a white-colored metal resembling, in some degree, antimony. It is soft, but so brittle as to be easily pulverized. Its specific gravity is 9.83, which may be increased somewhat by hammering. It melts at 480° Fahr., and may be coaled six or seven degrees below this point without fixing; but the BISMUTH. 131 moment it begins to solidify the temperature rises to 480°, and continues stationary till the whole mass is congealed. When the temperature of the metal is raised from 32° to 212° it expands y^n in length. Bismuth has the property, in a high degree, of increasing the fusibility of the metals with which it is incorporated, and is a common ingredient of the more fusible alloys, some of which melt in boiling water. One part of bismuth with 24 of tin is malleable, but the alloy of these metals becomes brittle by the addition of more bismuth. Bismuth unites readily with antimony, and in the proportion of one part or more of the former to two of the latter, it expands in the act of cooling. There are many other metals and alloys besides those already enumerated, but which have not been particularly described on account of their inutility in the laboratory for dental purposes. Among these may be mentioned iron, brass, bronze, etc., which are only employed for auxiliary purposes, and are both inconvenient and impracticable for dies by reason of their infusible nature and consequent contraction; nickel, on account, also, of its extreme infusibility and its tendency to render the alloy of which it is a component less fusible; sodium, on account of the changes produced on it by exposure to the air; potassium, on account of its extreme sensi- tiveness to the influence of low temperatures, being semi-fluid at 60° Fahr., nearly liquid at 92°, and entirely so at 120°; arscnic, because it volatilizes before fusing; cadmium, with no advantages above tin, on account of its scarcity and costliness; etc. CHAPTER XL GENERAL PROPERTIES OF ALLOYS, AND THEIR TREATMENT AND BEHAVIOR IN THE PROCESS OF COMPOUNDING. All alloys possess metallic lustre, are opaque, conduct heat and electricity, and, in a greater or less degree, are ductile, mal- leable, elastic, and sonorous. Some alloys, as brass and gong metal, are usually malleable in the cold, and brittle when hot. Metals sometimes unite in atomic ratios, forming compounds of definite or equivalent proportions of the component metals, as certain alloys of copper and zinc, gold and copper, gold and silver, mercurial alloys, etc., while, on the other hand, many are formed in all proportions, like mixtures of salt and water. Metals differ in respect to their affinity for each other, and do not, therefore, alloy with equal facility; thus it is difficult to unite silver and iron, but the former combines readily with gold, copper, or lead. The ductility of an alloy is, in general, less than that of its constituent metals, and this difference is, in some instances, remarkably prominent, as in the case of certain alloys of copper and tin, already mentioned. An alloy is generally harder than the mean hardness of its components, a property which, when taken in connection with their increased fusibility, gives to alloys peculiar value in the formation of dies for stamping purposes. To the rule stated, amalgams, or mercurial alloys, are cited as exceptions. The density of an alloy varies with the particular metals composing it, being generally either greater or less than the mean density of its several components. It is impossible to predict with certainty the melting point of an alloy from that of its separate constituents, but, gener- ally, the fusibility of the alloy is increased, sometimes in a most remarkable degree. The alloy of 5 parts of bismuth, 3 of lead, and 2 of tin is a striking example of this fact, this compound melting at 197°, while the mean melting point of 132 PROPERTIES AND TREATMENT OF ALLOYS. 133 its constituents is 514°. Silver solder is also a familiar illus- tration of the influence of alloying on the fusibility of metals: copper, melting at 1996°, and silver at 1873°, when combined, fuse at a heat much below that required to melt silver, the more fusible component of the alloy. Again, iron, which melts at a little less than 3000°, acquires almost the fusibility of gold when alloyed with the latter. Examples might be multiplied, but it will be sufficient to add that, in general, metallic alloys melt at a lower heat than is required to fuse the most refractory or infusible component, and sometimes than the most fusible ingredient. The color of an alloy cannot, in general, be inferred from that of its component metals; thus it would be conjectured that copper would be rendered very much paler by adding to it zinc in considerable quantities, but the fallacy of such an inference is at once shown by an examination of some of the rich-looking gold-colored varieties of brass, as Prince's metal, pinchbeck, and similor, composed each of nearly equal parts of copper and zinc; and Manheim gold, compounded of 3 parts copper and 1 of zinc. The affinity of an alloy for oxygen is greater than that of the separate metals, a phenomenon that is ascribed by Ure to the increase of affinity for oxygen which results from the tendency of one of the oxides to combine with the other ; by others it is attributed to galvanic action. According to Fara- day, 100 parts of steel, alloyed with one of platinum, is dis- solved with effervescence, in dilute sulphuric acid too weak to act with perceptible energy on common steel. It is offered in explanation of this fact that the steel is rendered positive by the presence of platinum. A similar illustration is afforded by the action of dilute acid on commercial zinc, which is usually an alloy of zinc with other metals. The action of air is, in general, less on alloys than on the separate metals composing them. To this, however, there are exceptions, as the alloy of 3 parts of lead and 1 of tin, which, when heated to redness, burns briskly into a red oxide. Some points of practical interest suggest themselves in con- 134 MECHANICAL DENTISTRY. nection with the behavior and proper management of alloys in the process of compounding. As metallic alloys can only be formed by fusion, and as the affinity of the metals composing them for oxygen is greatly increased by heat, especially those denominated base, it is important that this tendency, which is incompatible with the proportional accurateness of the compound, should be, as far as practicable, guarded against. Hence, various substances hav- ing a greater affinity for oxygen than the metals to be united, as oil or grease, rosin, powdered charcoal, etc., are generally added, coating the surface of the liquid metals, and which, by affording a protective covering, preserves, with little change, the proportions of the alloy. Some difficulty is occasionally experienced in obtaining a perfectly uniform alloy, on account of the different specific gravities of the metals composing it—each metal assuming the level due to its density. This partial separation is common to gold and silver, provided they have not been adequately stirred before pouring. This result is not so likely to occur when the metals employed are in small quantities and are sud- denly cooled, but when used in considerable masses and allowed to cool slowly, it is much favored by permitting the metals to fix themselves in the order of their separate densities. Hence, whenever a notable difference in the specific gravity of the metals exists, the fused mass should be briskly stirred imme- diately before the instant of pouring it, and should be made to solidify quickly. If uniformity be not obtained in this manner, it will be necessary to remelt, and repeat the process, if neces- sary, until the alloy is rendered sufficiently homogeneous. In alloying three or more metals differing greatly in fusi- bility, or that have but little affinity for each other, it is better to first unite those which most readily combine, and afterward, these with the remaining metal or metals. If, for example, it is desired to unite a small quantity of lead with brass or bronze, some difficulty would be experienced in forming the alloy by direct incorporation of the metals, but union could be readily effected by first melting the lead with zinc or tin, and then adding the melted copper. PART SECOND. ARTIFICIAL DENTURES. Before considering particularly the distinct and special methods employed in the construction of artificial dentures, such preliminary processes as are common, in some degree, to all, will, for the sake of convenient arrangement, and the avoidance of unnecessary repetition hereafter, be first considered. These processes relate:' 1. To the treatment of the mouth preparatory to the insertion of artificial teeth. 2. The manner of obtaining impressions of the mouth. 3. The manner of procuring and forming plaster models of the mouth. 4. Metal- lic dies and counter-dies. 135 CHAPTER I. TREATMENT OF THE MOUTH PREPARATORY TO THE INSERTION OF ARTIFICIAL DENTURES. It rarely occurs that all the structures of the mouth are in such condition as will render it proper to insert an artificial appliance without some preparatory treatment. This import- ant requirement cannot, in any material respect, be disregarded by the practitioner without endangering the utility and perma- nence of the substitute, and inflicting upon the patient a train of consequences alike distressing and pernicious. Every experi- enced dentist is familiar with the fact that an artificial substi- tute, resting upon diseased roots of teeth and impinging continually upon gums already irritable and inflamed, soon becomes a source not only of annoyance and discomfort to the patient, but is rendered, in a great degree, inefficient in the performance of some of its more important offices. There is, besides, a perpetual and cumulative aggravation of the morbid conditions, and, sooner or laler, irretrievable destruc- tion of the remaining natural organs will be induced. These consequences cannot be wholly averted by the most skillful manipulation, but they may be greatly magnified by a defect- ive execution of the work, or by a faulty adaptation of the. appliance to the parts in the mouth. Patients not unfrequently attempt, by every artifice or pretext that caprice or timidity may suggest, to persuade the operator to violate his own clear convictions of duty, but, unless under circumstances of peculiar exigency, he should be careful to guard himself against the imputation of incom- petency or bad faith by being peremptory and unyielding in his demands upon the patient to submit to the necessities and just requirements of the case, and no ordinary circumstance should influence him in opposition to his better informed judgment. The conditions usually met with, to which it will be neces- 136 PREPARATORY TREATMENT OF THE MOUTH. 137 sary to direct attention in the treatment of the mouth, are: 1. The presence of useless and diseased remains of teeth. 2. Accumulations of tartar. 3. Diseased states of the gums and mucous membrane. 4. Caries. Useless and Diseased Remains of Teeth.—It may be stated, as an absolute rule of practice, that all teeth, or remains of teeth, affected by incurable forms of disease, should be removed before inserting either partial or entire dentures. This recommendation must, however, be construed in the light of the curative resources of dental surgery and therapeutics. Many diseased conditions associated with the teeth that have heretofore been generally regarded as incurable, have, in the use of more radical and efficient remedial measures, proven amenable to such treatment as assures their retention for many years in a condition fitting them for important uses. A new impulse has of late been given to such conservative treat- ment of these organs with the view, chiefly, of utilizing them more generally for purposes of support in setting artificial crowns, and in the method of replacement known as " bridge work." The marked success which of late years has attended the treat- ment of diseased roots, and the increasing importance attached to them for the purposes mentioned, as well also as the essen- tial office they perform in preserving the structural integrity of the associated alveoli, and in maintaining the normal circula- tion and nutrition of the parts, would seem to justify the con- clusion that their extraction is plainly contra-indicated, save in rare and exceptional cases of intractable disease, in which case there is no question concerning the propriety or necessity of their removal. Their presence in connection with the substi- tute must, sooner or. later, become not only a source of annoy- ance and distress to the patient, but will, in all probability, lead ultimately to consequences of a still graver nature. Inflamma- tion and suppuration will be likely to be induced, or, if already present, will be aggravated, by the mobility and unaccustomed pressure of the substitute in the process of mastication, thus contaminating and vitiating the oral secretions, which act, by reason thereof, with increasing energy upon oxidizable materials 138 MECHANICAL DENTISTRY. present in the mouth, as well as upon the remaining natural teeth, while the contiguous parts, through their immediate con- nection or sympathetic relations with the structures of the mouth, respond to the local disturbances, and the case, in time, becomes complicated with those various distressing maladies about the head and face so commonly associated with diseased conditions of the oral cavity. At last, the patient, no longer able to endure the offensiveness and distress arising from the presence of the substitute in the mouth, or to properly masticate his food, is compelled to have the offending organs removed. The absorp- tion of the gums and processes which follows this operation, and the corresponding changes which occur therefrom in the form of the alveolar ridge, make it imperative either to reconstruct the piece or to supply the patient with an entirely new sub- stitute ; whereas, if due regard is had to the proper preparation of the mouth in the first instance, the patient may be spared such inflictions, and the operator the discredit which almost invariably attaches to the neglect of the measures recommended. Removal of' Salivary Calculus or Tartar.—The deposits of tartar which so frequently collect at the necks of the teeth, and under the free margins of the gum, are a prolific source of evil, inducing ultimate destruction of tKe investing membranes and contiguous alveoli, and as this deposit is continuous and progressive, following closely the wasting or destruction of the implicated tissue, teeth originally firm become in time not only unfitted for the proper performance of the functions required of them, but a source of diseased action in surrounding structures. Hence it becomes absolutely necessary, as it relates to the general health of the mouth, to thoroughly remove, with suitable instruments, all traces of this concretion from the teeth. If any considerable number of the teeth are found coated with tartar, and it is deposited in large quantities, it will be im- practicable, as a general thing, to remove thoroughly all remains of it at a single sitting. The operation should be repeated, therefore, from time to time, until every portion of it is com- pletely separated from the teeth, and the surface thus denuded smoothed and polished with appropriate instruments. In some complications characterized by suppurating processes and PREPARATORY TREATMENT OF THE MOUTH. 139 necrosed alveoli, as in so-called " Rigg's disease," or pyorrhoea alveolaris, the treatment must be more thorough and radical. Diseased Conditions of the Mucous Membrane and Gums.—It will seldom be necessary to institute treatment for the reduc- tion of inflammation and suppuration of the soft tissues of the mouth after removal of diseased roots and tartar, inasmuch as these conditions, being generally provoked by and associated with the latter, will spontaneously subside with the removal of the exciting causes. If, however, this does not occur within a reasonable time, relief may generally be obtained with the use, as a mouth-wash, of any of the remedies ordinarily employed, as dilute tincture of arnica or calendula, phenol sodique, etc. As a means of allaying soreness or tenderness of the gums after extraction, the author has had gratifying success in the use of Pond's extract of hamamelis. If there are morbid con- ditions of the soft tissues or osseous structures of the mouth, not immediately arising from the presence of diseased roots and tartar, they should be treated in accordance with the particular pathological conditions present. Caries or Decay of the Remaining Teeth.—In order that all the teeth which it is deemed advisable to retain in the mouth may be permanently preserved, it will be necessary to fill, or other- wise treat, such as may be affected by caries. This operation will be attended with more satisfactory results, and be accom- panied with less pain to the patient, and diminished risk of failure, when performed after the removal of the roots of teeth and tartar, and the restoration of diseased conditions of the mouth to health, as, in this case, there will be less irritability of the general system, and reduced sensitiveness of the teeth operated on. Surgical Treatment of the Mouth after the Extraction of Teeth. —In the operation of extracting preparatory to the insertion of artificial dentures, especially in cases accompanied by unavoid- able fracture of the processes, it sometimes happens that' loose and pendulous portions of gum remain, giving temporary annoyance to the patient. Any considerable excess of such tissue may be, in part at least, clipped off, while sharp and pro- truding portions of processes at other points should be removed, 140 MECHANICAL DENTISTRY. as, if they are allowed to remain, the gum closing over them will, in a short time, become irritated and inflamed, and exceed- ingly painful to the slightest pressure. If, in the course of a few weeks, prominences still remain, over which the mucous membrane is stretched and irritated or inflamed, as is more frequently the case around the sockets of the cuspidati, the membrane should be divided over such points with a lancet, and the sharp points of bone underneath broken down with suitable cutting instruments. Time Necessary to Elapse after the Extraction of Teeth before Inserting Artificial Dentures.—The time that should elapse after extracting the natural teeth, before replacing them with arti- ficial substitutes, will depend upon various circumstances. If the appliance is only intended to meet the wants of the indi- vidual until all the changes effected by absorption of the gums and processes are fully completed, it may be inserted in from one to three weeks, depending somewhat upon the number of teeth extracted, the extent of the injuries unavoidably inflicted upon the parts, and the virulence gf the diseased action present in the structures of the mouth at the time of the operation. If there are no unusual complications, and the space or spaces to be supplied are such as are made by the loss of only one or two teeth at intervals, the parts quickly assume their normal con- dition, and the piece to be temporarily worn may be applied within a few days. If, however, a greater number or all of the teeth have been removed, more or less inflammation and tenderness will be present for from ten days to two or three weeks, rendering the wearing of an artificial piece uncom- fortable to the patient, and in some degree mischievous by aggravating the morbid conditions already existing. Another objection to the too earty introduction of artificial substitutes into the mouth arises from the fact that the changes which occur in the ridge are much more rapid within the first few weeks after the extraction of the teeth than at any subsequent period, so that the plate, if inserted immediately or within a few days after such operation, will soon lose its bearing upon the ridge and become inefficient for masticating purposes, or may even fail to be retained in the mouth without much PREPARATORY TREATMENT OF THE MOUTH. 141 annoyance to the patient. Two or more weeks, therefore, should elapse before applying the substitute. In the meantime, the patient should be seen frequently, and such medical or surgical treatment adopted from time to time as the case may demand. The time occupied in the completion of those changes which occur in the alveolar border after the extraction of all or any considerable number of the teeth cannot be definitely stated, but will range from five to eighteen months or more, according to the amount of superfluous structures to be removed, the density of the osseous tissues,*and the functional activity of the absorbents. In all cases, ample time should be permitted to elapse in order that no appreciable change in the form of the parts may take place after the appliance has been permanently adjusted. It should be remembered, however, that there is no period of time when the changes in the maxillary bones which follow the extraction of the natural teeth may be said to be absolutely completed. It is well known that, in exceptional cases, renewed absorption may occur long after the time when it is supposed to be completed, extending in some cases quite beyond the ordinary limits. This is ascribed by many to mis- fitting plates, or to some particular quality of the material used as a base, notably vulcanized rubber. While there may be some plausibility in this view, it can hardly be accepted as final or conclusive. That the unusual destruction or wasting away of involved tissue is induced by some abnormal action of the absorbent or nutritive processes is without question, but whether this is induced by local or systemic causes remains in doubt. " CHAPTER II. MATERIALS, APPLIANCES, AND METHODS EMPLOYED IN OBTAINING IMPRESSIONS OF THE MOUTH. In the process of constructing a dental substitute, it is of the first importance that as accurate an impression as possible should be obtained of all those parts of the mouth with which the appliance is any way connected. If this important prelimi- nary step is, in any essential respect, imperfectly performed, the ultimate utility of the artificial fixture will either be greatly impaired or wholly destroyed, notwithstanding all the subsequent manipulations may be most carefully and skillfully performed. The operator, therefore, should not only avail himself of every appliance and facility that will enable him to attain the' most perfect results, but should have an exact and intelligent acquaintance with the nature, properties, and adaptability of the impression materials used. The substances ordinarily employed for this purpose are: beeswax; combinations of beeswax, paraffine, and gutta- percha; modeling composition; gutta-percha; and plaster-of- Paris. Some diversity of opinion exists as to the relative value of these several impression materials, and the choice of any one of the class is generally determined by individual notions of the indications to be fulfilled in any given case, and the supposed special adaptability of the material to the* fulfillment of such indications. In the case of entire dentures, where there is a near ap- proach to uniformity of hardness or softness, and consequent uniformity of resistance, in the tissues of the mouth, plaster, of the proper consistence, unquestionably takes precedence of all other materials for the purpose, and the almost universal preference given to it in such cases is a virtual confession of its superior fitness. Its capability, beyond that of all the other substances mentioned, of securing the most perfect 142 IMPRESSIONS OF THE MOUTH. 143 impression of the several parts in their undisturbed relation to each other is unquestioned, and it may be affirmed with positiveness that, except, possibly, in the case of plastic bases, where there is no compensation for the slight expansion of the plaster, if all the surfaces on which the substitute rests were equally pliant or equally resistant to forces applied to them, no other material would be required. But, strictly speaking, this condition of uniformity never prevails, and in many cases there is a marked departure from it. The most common and troublesome complication of this kind occurs where there is a more or less pliable or yielding condition of the alveolar ridge associated with a comparatively hard and resistant surface along the median line of the floor of the palate, being more pronounced near the soft palate. In such cases, this inequality of softness and hardness, if considerable, prevents a properly balanced contact and pressure of a substitute constructed from an impression of the parts in a state of repose. Thus, for example, in the case of a perfectly fitting denture secured in the manner just stated, if the ridge along the mesial line of the palatal vault is more than usually hard and prominent, and the lateral portion of the arch and alveolar ridge relatively soft and yielding, the substitute, meeting with a fixed point of resistance at the floor of the palate, will prevent the lateral walls and ridge from being sufficiently compressed on the application of retaining forces, whether atmospheric, adhesive or capillary, or of all combined. Hence, when forcible pressure is made on one side over the ridge, as in mastication, the substitute, impinging or riding upon the central resistant surface of the arch, as upon a pivotal point, will be detached and thrown off from the opposite side. If the same yielding condition of the anterior portion of the ridge prevails, the appliance, when forces are applied to the front teeth, will be dislodged posteriorly. The proposed remedy for the instability of the substitute, resulting from the conditions mentioned, consists in so con- structing the dental appliance that, when applied to the mouth, and subjected to the action of the retaining forces, a degree of resistance in those parts where the soft tissues are in excess 144 MECHANICAL DENTISTRY. will, through compression of the tissues, be secured, equal, or nearly so, to that presented by the central portion of the arch; in other words, by establishing an equilibrium of pressure or resistance in all the parts on which the plate rests. It is generally believed that certain forms of impression material, through the pressure they exert, are capable of con- tributing materially to this result. This is predicated on the assumption that the pressure they exert1 is sufficient to com- press or displace the tissues in question. It may be well to inquire if the compressing power of these substances, in the cases under consideration, has not been overrated. If by the term compression, as used in this connection, is meant conden- sation or diminished bulk of tissue, certainly no such result could be obtained by any force capable of being applied within the mouth, however hard and resistant the material used. Any change in the normal configuration of the arch and ridges possible, in the use of such substances must, therefore, result, not in condensation, but in displacement of tissue. It can be readily understood how this displacement may occur along the summit line of the ridge in cases characterized by considerable excess of gum material lying in loose and gristly folds, chiefly in front of the bicuspids, and associated generally with the long use of partial dentures. In applying pressure in such cases, the effect would be to force these mobile, structures out of their customary relations to the ridge and arch. How far such a procedure is in accordance with the principles of right practice must be submitted to individual judgment. That any change in the mere relative position of such loose structures to the ridge would contribute in any appreciable manner to the stability of the substitute is not very apparent. Within the limits of the maxillary arch or palatal vault, the fossas or depressions lying on either side of the central line are filled more or less completely with a mass of comparatively soft but elastic areolar, cellular, or connective tissue, which, in its unchanged condition, is thought to practically interfere, in many cases, with a properly balanced contact or bearing of the substitute. A partial remedy, at least, it is claimed by many, may be found in the use of some impression material of suffi- IMPRESSIONS OF THE MOUTH. 145 cient firmness to compress or displace such tissues sufficientlv to afford points of resistance to the substitute equal, or nearly so, to that offered by the median line of the arch. The dis- placement here, if any, would be in the direction of the least resistance, or toward the velum or soft palate, all portions of the arch anterior to the latter, except in the case of an air chamber, offering effectual resistance to displacement in any other direction. When the nature and relations of these as- sociated soft structures of the mouth are considered, it is highly improbable, and we think impossible, that any appreciable change of contour within the arch could take place on the application of any force applied in the use of either wax, modeling composition, or gutta percha. If these conclusions should be justified by experimental tests, as we believe they would be, it would be practically unimportant, except where the tissues of the ridge are characterized by unusual mobility, what material was used, provided a perfect impression could be obtained with it. The paramount merits of plaster, as a substance capable beyond question of fulfilling perfectly this requirement, would therefore recommend it, in ordinary cases, in preference to any other material. That other substances have a special and distinctive value for impression purposes in connection with partial dentures, will not be gainsayed, but their manifest unfitness for the same purpose in all cases of edentulous jaws render their employment unadvisable, save, perhaps, in rare and exceptional cases. One possible result of the use of any of the impression materials named, exclusive of plaster, both in full and partial cases, must always render their employment of doubtful expe- diency whenever plaster can be successfully manipulated for the same purpose, namely, their great liability to distortion on the application of forces necessary to detach them from the mouth, and the impossibility of detecting any change of form until the error, too late for correction, is revealed in a faulty adaptation of the finished piece to the mouth. It must not, however, be understood from this that it is impossible to secure a practically accurate impression of the parts in the use of these materials. The purpose is, rather, to impress the im- 10 146 MECHANICAL DENTISTRY. portance and absolute necessity of extraordinary care in their manipulation in order to secure satisfactory results. The rela- tive liability of the several substances named to such disturb- ance of form, and the precautions necessary to be taken to avoid such an unfortunate and generally fatal accident, will be more particularly noticed when we come to treat of them indi- vidually as impression materials. This will be done in the order before named. Beeswax.—There are two varieties of this substance in common use, the yellow and white wax. The yellow variety is esteemed preferable to the white on account of its superior toughness; the latter being, to some extent, disintegrated, or rendered less tenacious, in the process of bleaching, but is frequently used and is preferred by many on account of its color. The more desirable properties of the yellow wax are often impaired by the admixture with it of tallow, with which it is, for mercenary purposes, frequently contaminated. The presence of tallow may be detected by its characteristic odor, and by the whitish or pale yellow color it imparts to the wax, which in its pure state, is of a deep, bright straw color. Wax used for impressions should always be kept in con- venient form for immediate use, and may be prepared either by warming it until sufficiently soft and then rolling or press- ing it into thin sheets; or having melted it in a properly formed vessel, immerse in it a strip of thin board, previously moistened, and withdraw quickly; this is repeated as the suc- cessive layers cool, until a coating of sufficient thickness is obtained. The latter is a convenient method of obtaining sheets of wax of a uniform thickness, a form frequently required for various purposes in the dental laboratory. The following directions in the use of wax will apply also to its combinations with paraffine and gutta-percha, and also to modeling composition. Manner of Obtaining an Impression of the Mouth in Wax, for Partial Upper Dentures.—Until within the past few years, wax has been used almost exclusively for the purpose of obtaining an impression of the mouth in those cases where any number of the natural teeth remain in either or both jaws, and, for this IMPRESSIONS OF THE MOUTH. 147 purpose, is ordinarily more convenient and manageable than plaster, and, if carefully manipulated, will secure in many cases a sufficiently accurate impression of the parts. Before preparing the wax, a suitable impression cup or tray should be selected, conforming as nearly as possible in size and shape to the general form of the arch and ridge. The proper size should always be determined by trial of the empty cup in the mouth before taking the impression. Impression cups are made from a variety of substances, as sheet-tin, porcelain, vulcanized rubber, and Britannia metal, and sometimes, in order to meet the requirements of special or exceptional cases, either brass, copper, block-tin, or gutta-percha may be used. Cups constructed of sheet-tin, which any tinner can readily make to order, were formerly very generally used for partial cases, and if proper care is taken not to inflict injury to the lips and soft parts with the thin, sharp edges when introducing and pressing the cup to its place in the mouth, they may be used with satisfaction. Porcelain cups are adapted to the use of the several impres- sion materials named, except plaster, the latter being quite liable to part from their glazed surfaces on the application of the necessary force to detach the impression, leaving the plaster in the mouth. Aside from their purity and attractive appearance, they possess no advantages that would make them preferable to Britannia cups, while they are objectionable because of their liability to injury, and entire incapability of being changed in form to meet special requirements. When used in connection with wax, they should be slightly heated before the former is introduced. Hard rubber trays, of any desired form, may be readily made from plaster models by any one accustomed to rubber work, and are chiefly adapted to the use of plaster, as they are not readily cleansed if other plastic substances are employed. Their form may be materially changed by immersing them for a few moments in boiling water. Britannia metal, however, meets most fully all the require- ments of an impression cup, and is well adapted to the use of 148 MECHANICAL DENTISTRY. any of the impression materials commonly employed. The great variety in form and size found at dental depots will amply meet all the requirements of ordinary cases. For un- usual or abnormal conditions requiring exceptional forms of trays, the operator must construct for himself such appliances, either swaged or cast, as will best serve his purpose in the individual case. Whatever cup is selected in securing an impression in wax for a partial upper case, it should be large enough to embrace the alveolar ridge, leaving a space of nearly a fourth of an inch between the rim and the external wall of the alveolar ridge. In cases requiring an impression of a limited portion only of the arch, as where clasps are used, the form of cup shown in Fig. 61 may be used. If it is designed to employ a plate covering nearly or quite all of the hard palate, a cup Fig. 61. Fig. 62. (Fig. 62) of the same general form, but with its central portion extended posteriorly, will be found especially well adapted to the purpose. A cup designed for similar cases by Dr. Wardle, exhibited in Fig. 63, is particularly adapted to high arches, being pro- vided with a movable palate plate, by which the central portion of the impression material is effectually forced into the highest portions of the palatal arch, and laterally against the sides and necks of the remaining teeth. Having selected a cup of the proper form and size, the wax should be warmed in a spirit flame until it acquires about the consistence of freshly-made putty. Wax is sometimes softened by immersing it in hot water, but the dry heat is preferable, as the former seems to impair, to some extent, its toughness and continuity. In taking the impression the operator should IMPRESSIONS OF THE MOUTH. 149 place himself behind and to the right of the patient, and should be sufficiently raised above the latter to enable him to manipulate with the greatest ease and certainty, and at the same time to command as full and unobstructed a view of the interior of the mouth as possible. The cup with the wax arranged should then be introduced into the mouth without unnecessary delay. To do this properly, and without subject- ing the patient to annoyance, will occasionally require some care and expertness, on account of the disproportionate size of the cup and orifice of the mouth. An ample and expanded jaw, for example, is frequently associated with a small mouth, and if in addition to this the sphincter muscle of the mouth happens to be rigid and unyielding, the introduction of a cup Fig. 63. of sufficient size may be attended with some little difficulty and embarrassment. This impediment, however, may be readily overcome in most cases by presenting the cup obliquely to the mouth, one side resting against, and pressing outward, the corner of the mouth, while—as the opposite corner is extended with the first and second fingers of the left hand—the cup is passed in with a rotary movement. When the cup is within the mouth it should be carefully adjusted over the ridge before pressing it up, so that no por- tions of the rim may cut into the soft tissues of the mouth, an accident liable to happen without care, arid which wall make it necessary, in most cases, to withdraw the cup before the im- pression is complete. The proper position of the cup in the 150 MECHANICAL DENTISTRY. mouth secured, it should be held firmly with the thumb rest- ing on the handle above, and two or more of the fingers on the under surface, when it is slowly but steadily and forcibly pressed against the parts above until the ridge is completely imbedded, and the wax carried closely against the roof of the mouth. The cup should then be held stationary with one hand, while with the fingers of the other the wax around the margins of the cup should be pressed closely into all the depressions occurring on the outside of the ridge between the remaining teeth, or wherever irregularities may present them- selves on the external border of the jaw. The finger should also be passed to the roof of the mouth at the central and posterior edge of the cup, making pressure against the pro- truding wax upward and forward into the anterior and deeper portions of the palatal arch. When the operation has been conducted thus far, and before removing the cup, gentle up- ward pressure upon the latter may again be made—not enough to move the entire body of wax, but only sufficient to correct any partial displacement that may have happened from acci- dental tilting or lateral movement of the cup during the concluding manipulations. After the wax has remained in the mouth long enough to become in some degree hardened, it should be carefully detached by gentle traction upon the cup, and removed from the mouth in the same manner in which it was introduced; care being taken not to displace the wax or otherwise mar the impression. The force with which the wax impression will adhere to the mucous surfaces on the complete exclusion of air is oftentimes very considerable, and will require a corresponding tractive force to dislodge it. In applying this force, it should be borne in mind that, in the very plastic condition in which the wax is applied to the mouth, it is not only very soft and yielding, but, being wholly inelastic, is incapable of recovering its form when temporarily disturbed, and that, consequently, any dis- tortion of the impression occurring from the force applied in removing it from the mouth will be permanent, and pos- sibly fatal. It should, therefore, as has already been stated, be allowed to remain in the mouth long enough to become some- IMPRESSIONS OF THE MOUTH. 151 what hardened, say from three to five minutes, and this process mav be facilitated by holding against the cup a napkin satu- rated with cold water. The proper degree of hardness will, however, depend upon the circumstances of the case. If the remaining teeth present to each other parallel walls, or nearly so, permitting an easy escape of the wax from the interdental spaces, the greatest practicable degree of hardness that can be attained is desirable. If, on the other hand, these spaces are V-shaped or dovetailed, as is very generally the case where the teeth to be replaced have been long absent, the impression should be removed while the wax is somewhat plastic, permit- ting a ready separation by such displacement of wax immedi- ately around the adjoining teeth as must always occur in these cases in the use of wax. In proportion as the wax is rendered hard and unyielding will be the resistance to its escape from these spaces, and the dangers of change of form in parts of the impression more or less remote from them augmented. It is, therefore, unadvisable in such cases to produce hardness arti- ficially by the application of ice or cold water. Under similar conditions, the same precaution should be taken against over- hardening in the use of gutta-percha and modeling composition. Imperfections occurring from displacement or dragging of wax on removal from the mouth, if inconsiderable, may be remedied with tolerable accuracy by subsequent carving of the plaster model, and this may be aided by a comparison of the plaster representation of the teeth with those in the mouth. If, however, the interdental undercuts, and those associated with bell-crowned teeth at other points, are more pronounced, it is better to use either'the modeling composition or gutta percha, and if in excess, plaster. Inasmuch as it is necessary, in constructing partial sets of teeth, where swaged base plates are used, to be provided with two or more plaster models, and as the latter cannot well be obtained in perfect condition from a single impression, it is better that at least two of the latter should be secured in the first instance. Manner of Obtaining an Impression of the Lower Jaw in Wax, for Partial Dentures—If the case is one where teeth at intervals 152 MECHANICAL DENTISTRY. are to be supplied, the form of cup used in taking an impres- sion for an entire lower denture (Fig. 67) may be employed ; or if the vacuity exists in the front part of the ridge only, then one like that represented in Fig. 61 will answer the purpose. If, how- ever, as is more generally the case, the front teeth remain, and those posterior to the cuspids or bicuspids are to be replaced, the form of cup exhibited in Fig. 64 should be used, a portion being cut out from the front part of it, forming a vacuity which receives and permits an unobstructive passage of the front teeth. As the latter are often very long, it is difficult, with the ordinary form of cup, to press the wax down fairly upon the ridge behind without bringing their cutting edges prematurely in contact with the floor of the cup in front. Instead of the opening represented in the cup, however, it will be sufficient in most cases to have it formed with a depression in front of adequate depth to receive the points of the anterior teeth. In taking an impression of the lower jaw, after having prepared and arranged the wax by softening and filling the groove of the cup flush with the margins, the operator may first take a position to the right and back of the patient, and introduce the cup into the mouth in the manner heretofore described, when he should pass to the front of the patient, and having adjusted the cup properly over the ridge, the first two or three fingers of each hand should be placed upon the top of each side of the cup, and a thumb upon each side and under- neath the jaw, and firm and steady pressure made until the ridge is wholly imbedded. Before final adjustment of the wax to the ridge, however, care should be taken not to enclose any loose folds of membrane along the line of junction between the ridge and cheeks, or of loose tissue lying on the inside near the base of the tongue. To avoid the former, immediately before final pressure is made, the cheek should be distended and drawn outward with the finger, first on one side and then on IMPRESSIONS OF THE MOUTH. 153 the other, holding the cup, in the meanwhile, steadily in place. The loose and movable tissues on the inside will be drawn away from the ridge somewhat if the patient is directed to raise the tongue well toward the roof of the mouth. Some little additional pressure may then be made upon the cup, after which the wax should be pressed in around the margins of the cup, both externally and within, when the impression is care- fully removed from the mouth, observing the precautions stated when treating of wax and other allied substances. Manner of Obtaining an Impression of the Mouth in Wax for Entire Upper Dentures.—The form of cup employed in taking an impression of the upper jaw, in the absence of all the natural teeth, is seen in Fig. 65. A number of these, corre- sponding as nearly as possible in FlG 65 form and size to the various modi- fications in the configuration and dimensions of the maxillary arch, should be kept conveniently at hand. If the teeth have been re- cently extracted, the wax should be prepared somewhat softer than usual, to prevent displacement of the gums, which, in their unabsorbed condition, possess more or less mobility. The cup should be filled flush with the edges, and built up in the centre if the depth of the palatal vault requires it, and the wax properly trimmed; it is then in- troduced into the mouth and adjusted to the ridge, as already described, and pressed to the jaw with sufficient force to fully encase all the parts to which the substitute is ultimately to be applied. The wax, as the cup is pressed up, has a tendency to roll out at its edges and thus depart from the upper and outer portions of the ridge; hence care must be taken to press the wax in around the marginal portions of the cup, filling up any depressions or fosses that may occur on the external border of the jaw. It is particularly necessary to observe this precaution whenever the ridge overhangs, as is prominently the case for the first few months after the extraction of the teeth. If the impression is an accurate one, some difficulty is occa- 154 MECHANICAL DENTISTRY. sionally experienced in detaching it from the mouth, on account of the thorough exclusion of air from between it and the mouth, the wax being held firmly in place by adhesive force ; in which event it is only necessary to admit the air between the two; and this may generally be readily effected by placing the finger against the jaw on one side and above the wax, pressing firmly toward the centre of the arch and upward, dragging the mucous membrane somewhat from the edge of the cup, and at the same time depressing the latter on the same side. A small portion of air being admitted, it will soon diffuse itself between the adhering surfaces and allow the wax to be readily detached. To harden the wax, and thereby prevent it from dragging at those points where the ridge over- hangs, or to prevent any change of form on the application of sufficient force to detach it from the mouth when it adheres Fig. 66. with great tenacity, a cup has been constructed with a chamber underneath, into which a stream of cold water is admitted. Two short pipes, as will be seen by reference to Fig. 66, com- municate with the chamber, and these again connect with a double tube fitting them closely, and united at the other end with two gum-elastic tubes—one communicating with a vessel of water conveniently placed and provided with a stop-cock, the other leading to a spittoon or other waste place. The two portions of pipe may be disconnected when not in use. After taking an impression with this cup, and before removing the wax from the mouth, the two portions of pipe are connected and a continuous current of cold water passed through the chamber by turning the faucet connected with the tank; when sufficiently hard, the wax is removed from the mouth before IMPRESSIONS OF THE MOUTH. 155 disjointing the pipes, to prevent the water from flowing upon the patient. This object can be accomplished, however, equally well, and much more conveniently, by applying to the cup, for several minutes, a napkin saturated with ice-cold water, or enclosing a piece of ice. To provide more perfectly against failure of the wax being carried closely against the roof of the mouth in cases where the palatal vault is very deep, a piece may be cut from the central part of the cup, the wax being pressed at this point up- ward and forward into the deeper portions of the palatal fossa; or a still better expedient Avill be found in the use of the Wardle cup, shown in Fig. 63. The author would repeat, in this connection, his conviction that it is impracticable, in most cases, to obtain a faultless impression of the mouth in wax, for full upper dentures. There are points, not readily accessible to the fingers, where the wax departs from the external and posterior borders of the jaw, and is not, therefore, susceptible of easy correction; besides, when reached and the remedy applied, there is no certain assurance that in pressing the wax in at one point we are not displacing it at another. The same uncertainty in regard to results also attaches to the use of the modeling composition and gutta-percha in these cases. For this reason, we invari- ably use plaster in these cases, and we have sufficient reason to believe that the results are more uniformly successful. Manner of Obtaining an Impression of the Lovoer Jaw in Wax, for Entire Dentures.—The method pursued in securing an im- pression of the lower jaw in wax for an entire denture differs in no essential respect from that described when taking an impres- sion for lower partial pieces, the form of cup being represented in Fig. 07. When the parts are im- bedded in the wax, the latter should be pressed in around the inner border of the holder, but more especially near the posterior part of the ridge on each side where the latter overhangs and 156 MECHANICAL DENTISTRY. approximate each other, forming corresponding excavations underneath. After adjusting the wax to the ridge along the border of the cup, the latter should again be pressed directly down upon the jaw before removing it, to correct any partial deformity that may have occurred during the previous man- ipulations. Modeling Composition, which of late years has largely super- seded the use of wax for impressions, is compounded of gum dammar, stearine, French chalk, carmine for coloring, and some perfume. The consistence of the mass depends upon the relative quantity of stearine and chalk introduced, the grades as manufactured being designated as soft, medium, and hard. This material takes a sharper impression of the parts than wax while its elastic property makes it especially suitable where there are overhanging ridges, irregularly arranged and bell-crowned teeth, and dovetailed interdental spaces. It is prepared for use by softening it either with dry heat, or by im- mersing it in hot water. When sufficiently plastic, it is intro- duced into a cup sufficiently heated to render the material somewhat adhesive. Before removing it from the mouth, it should be cooled some- what in order to preserve its form unchanged. Excessive hardness, however, should be avoided where portions are pressed into unusual undercut spaces, as the force necessary to detach it in such cases may produce deformity of the body of the impression more or less remote from the teeth and spaces mentioned. When removed from the mouth, it should be immediately dipped in cold water. The general manipula- tion of the compound in the mouth, both in full and partial cases, is the same as that described when wax is used, and the same care should be observed when removing the impression from the mouth. It is readily separated from the plaster model by immersing both in hot water until the impression material is quite soft, being careful not to overheat it. Gutta-percha—This substance, which is especially adapted to the class of partial cases already referred to, is perhaps not as generally employed as its distinctive merits warrant. It pos- sesses in a considerable degree the property of elasticity so IMPRESSIONS OF THE MOUTH. 157 necessary to a faultless impression in partial cases characterized by abnormal conditions as to the form and position of the remaining teeth. Of gutta-percha, Dr. W. C. Coffin, of Eng- land, says: "As to the material itself, the pink preparation made for many years by the Gutta-percha Company, when freshly prepared, left nothing to be desired, if only not treated according to the directions sent out by the depots. A careful analysis showed this to consist of 56.8 per cent, of very finely ground and pure oxide of zinc and 9 per cent, of vermilion. Its working properties depended, however, on the quality of the gutta-percha itself, which varies immensely in the whole- sale market. A satisfactory sample is distinguished by the strong smell characteristic of the fresh gum, its great pliability, toughness and absence of brittleness when cold, and its freedom from stickiness when wet at the temperatures below 212° F. After using a few times it becomes more plastic with heat and gives sharper casts, but with age and much use, it rapidly deteriorates." The method of preparing it for impressions requires more care than when the materials heretofore mentioned are used. It is customary to soften it in water near the boiling tempera- ture, say from 180° to 200° F. When sufficiently plastic, remove, press it with the fingers, kept wet, into the cup, and just before introducing it into the mouth, chill the surface by dipping it for a moment into cold water. It is then introduced into the mouth, and treated in all respects just the same as when using wax or modeling composition. Like the latter, it should be cooled before removing from the mouth, and by the same means, but extreme hardness, where there are pronounced undercuts, should be guarded against, as its extreme rigidity in this condition would, in such cases, render the removal of the impression exceedingly difficult. The following is Dr. Coffin's method of preparing and using gutta-percha: " In the process, a basin of cold water is provided, and another, lined with cloth, is filled with boiling water. In this gutta-percha in tolerably thin sheets is placed, and im- mediately softens; it is then lifted out on a smooth stick or glass rod and just dipped into cold water for a second. It may 158 MECHANICAL DENTISTRY. then be manipulated with wet fingers and placed in the cup. Becoming thus somewhat chilled, the filled cup is put into the hot water again for half a minute, then just dipped into the cold and placed in the mouth. It should be kept in the mouth for a minute and a half or two minutes, and then quickly removed, and placed at once in cold water." Gutta-percha contracts much more on cooling than either of the substances heretofore mentioned, and it is this property that gives it special value in cases where plastic materials, as rubber and celluloid, are used as bases. The contraction of the gutta- percha impression compensates, in a great measure at least, for the expansion of the plaster model, and in this way secures a more perfect adaptation of the substitute. For the same reason it would be contra-indicated in the case of swaged plates, inas- much as the contraction of the metallic die would be super- added to that of the gutta-percha. The gutta-percha impression may be removed from the plaster model in the same manner as described in the use of modeling composition. Plaster-of-Paris.—Plaster-of-Paris, or technically, calcium sul- phate, has been long employed in taking impressions of the mouth for entire dentures, and more recently, and to a more limited extent, for partial cases. For entire dentures, it has almost entirely superseded the use of all other materials on account of its capability of receiving a practically faultless imprint of the parts on which the substitute rests. The same quality of exactness recommends it also in partial cases where conditions exist that render an accurate impression of the parts with other materials impossible. Plaster is derived from gypsum by a process of calcination. The latter, or gypsum, is a common mineral, frequently crystal- lized, oftener amorphous, and oftentimes forming rock masses. Its transparent variety, called selenite, sometimes occurs in large plates, which have been used for windows. It also fre- quently occurs in aggregated needle-like crystals, and is then called fibrous gypsum. In its amorphous condition, when compact and translucent, it is named alabaster. More com- monly it is white, opaque, and soft, and is then called snowy IMPRESSIONS OF THE MOUTH. 159 gypsum. The most important deposits known are those of the Paris basin at Montmartre, from which it has taken the com- mon name of plaster-of-Paris. In the preparation of plaster, as used in the arts, the gypsum rock is ground between buhr-stones until it is reduced to a fine powder, when it is calcined by being heated in kettles or stills, the combining water being thus driven off. If, in this condi- tion, it is again mixed with water, the latter recombines with it, the mass becoming first plastic, and then solid. Hence, it is admirably adapted to a great variety of modeling processes. In its ordinary calcined form, plaster absorbs moisture from the atmosphere, and should, therefore, be carefully protected from dampness. Should the latter occur, the uncombined moisture may be driven off by exposing the plaster to a moderate heat in a shallow pan or other suitable vessel. In the process of hardening, after having been made plastic by the addition of water, more or less expansion of the mass, both during, and for a time after, solidification, takes place, varying with the kind of plaster used, and the various methods employed in preparing it for molding purposes. As hardness and expansion are conditions of great practical moment to the dentist in the use of this indispensable material, the author feels warranted. in quoting entire the following test experiments conducted by Dr. Stewart J. Spence, of San Francisco, Cal., made expressly for the purpose of obtaining the maximum of hardness with the minimum of expansion in the use of plaster under the varying conditions alluded to. Dr. S. says:— " The tests were made in a full upper celluloid blank, with various plasters, mixed in various ways, and with other materials, viz., alum, salt, sand, and marble-dust. • The expan- sion of the cast prevented it from fitting again in the blank, and showed the space between them, which varied from one to five thicknesses of note-paper. " Tests of various plasters :— " 1. The best S. S. White plaster, mixed plain (i. e., without alum, salt, etc), showed the least expansion, but was much the softest after setting. 160 MECHANICAL DENTISTRY. "2. The best plasterer's plaster, mixed plain, set hard, with moderate expansion. "3. Coarse builder's plaster set very hard but with great expansion. " Different samples of plaster, even when apparently alike, acted quite differently, especially when mixed with alum, some then becoming too porous and soft for any use, though setting hard without it. Most of these experiments were made with a sample of the best plasterer's plaster, which worked well with alum. " Tests were made in mixing plaster :— " 1. Mixed thick, and stirred about ten seconds. " 2. Mixed thin, and stirred about a minute. " 3. Mixed of medium consistence, and poured immediately. " Contrary to expectation, the last showed equal hardness with the two former, and but about half their expansion. " Further experiments were made on this line, testing the effects of duration of stirring and consistence of the ' mix' on the hardness and expansion of the cast. Firstly, three mixes were made, stirred the same length of time, but of different consistences:— " 1. Mixed very thin. " 2. Mixed very thick. " 3. Mixed of medium consistence. " The last showed greatest hardness and least expansion. Beyond a certain consistence, casts are not made harder by thick mixing, friability and porosity coming in to counteract the hardness gained thereby. " The next test had reference to duration of stirring. From the same cupful of plaster were poured— " 1. Mixed medium thick and poured immediately. " 2. Mixed medium thick and stirred two minutes. " The latter set almost immediately after being poured, expan- sion commenced very quickly, and continued, till by next day it had increased to at least five times that of No. 1. It was also the softer. So much for thick mixing and long stirring. " Thus, it was found that by mixing plaster of medium con- sistence and pouring immediately the casts made thereby set IMPRESSIONS OF THE MOUTH. 161 harder, expanded less, and the expansion set in much slower than by any other mode of mixing; the only drawback being that it set more slowly. " It still remained to be seen whether the same good results would accompany this method of mixing when alum was used. Three casts were made to test this, which clearly demonstrated that the same good results followed that method. " Tests were made to decide if thickness of the model affected the space made by expansion between its roof and the blank :— "1. A cast was made about one-sixth of an inch thick. 2. Another was half an inch. 3. About one inch. 4. About two inches. Contrary to expectation, that two inches thick showed no more expansion than that of only one-sixth of an inch. So with the others. " Experiments were then made by mixing with plaster, sand, marble, salt, and pulverized alum:— " Marble Dust.—This did not perceptibly increase the hardness or affect the expansion. u Sand,—This seemed to increase to some extent both the hardness and expansion. " Salt.—This materially lessened the expansion and increased the softness. It reduced the expansion of the S. S. White plaster to practically nothing. It also hastened setting when used in small quantities. The more salt used the softer was the cast but the smaller the expansion. " Alum.—About ten grains to the heaping tablespoonful of plaster gave the best results, reducing expansion to the mini- mum. I first mix the alum with the water, then the plaster. After some search I found a plaster which would set hard with alum, much harder than without it; but most plasters set soft with it; and all softened very much on boiling, and remained so when dry. This was the great objection, and mixing with sand or marble dust did not remedy it. For closing flasks with wet heat this is objectionable, so much so in some plasters as to absolutely contraindicate the use of alum, especially with celluloid. " Tests were made of casts in water:— "1. A cast mixed with alum and boiled about an hour became n • 162 MECHANICAL DENTISTRY. soft, but did not expand, and even seemed to have slightly con- tracted. " 2. A cast mixed thick, without alum, etc., and boiled for an hour, softened slightly and expanded. " 3. A cast ordinarily mixed, soaked in cold water several hours, showed no appreciable softening or expansion. " An important point noticed while conducting these experi- ments was that the casts continued to expand for two or three days, and that for a few minutes after setting the expansion was imperceptible, indicating that this period should be seized for obtaining the model from a plaster impression, and that the model should be used as soon as possible. After a few days, expansion ceased. I have made plaster set harder by drying it over a fire for an hour or two, before mixing. It must not be used while hot. " It is well known that casts can be hardened by heat, expel- ling the water of crystallization. Perhaps it is not so well known that casts thus hardened become much softer in boiling water than if not so dried. In fact, this drying can be carried so far as to render them readily pulverized under slight pres- sure. " I am informed that the best results can be obtained by mixing plaster, alum and water; then re-calcine." In the foregoing experiments, where Dr. Spence treats of alum as an ingredient of plaster mixtures, he states that its effect is to make most plasters set soft. The particular salt used by him in these experiments was the ammonia alum, or sulphate of alumina and ammonia. Mr. Fletcher, of England, alluding to this latter statement, says: " Alum, as properly understood, means the sulphate of alumina and potash (potash alum). Its action with plaster-of-Paris is totally different from that of ammonia alum, which for some years past has been sold in the place of the potash salt, to which the name was originally given. A solution of potash alum, boiling hot, in- stead of softening plaster, will make it so hard that it is difficult to cut or break, and it will cause plaster which has lost its power of setting totally to set again, although not sufficiently hard for use." Dr. Spence, in subsequent experiments with the IMPRESSIONS OF THE MOUTH. 163 use of potash alum, was unable to obtain the results claimed for it as above stated. If Mr. Fletcher's statement should be verified, the ascribed property would give great additional value to alum as an in- gredient in plaster mixtures, especially for models used in con- nection with the vegetable plastic bases, since, according to Dr. Spence, the minimum of expansion being secured in its com- bination with plaster, and also the maximum of hardness as claimed by Mr. Fletcher, the best possible results might be an- ticipated in the cases indicated. The practical application of the facts established by the fore- going experimental tests may be briefly summarized as follows: In the use of the vegetable plastic substances, as rubber and celluloid, requiring the least practicable expansion of the plaster impression, and the greatest attainable hardness and non- expansion of the model, the best results will be obtained (1) by taking the,impression with the best S. S. White plaster made into a paste of medium consistence with water impregnated with potash alum in the proportion of ten grains to a heaping tablespoonful of plaster, placing it in the cup as soon as thoroughly mixed, and (2) filling the impression, immediately on its removal from the mouth, for the model, with a mixture of the best plasterer's plaster of the same consistence and com- position as used for the impression, and (3) the earliest practi- cable use of the model in the construction of the substitute. On the presumption of the absolute reliability of Dr. Spence's experiments, this mode of procedure would give, practically, a perfectly fitting substitute in the use of the substances named. In the case of cast metal bases, the almost inappreciable ex- pansion of a model obtained by the means just described would be compensated for by the slight contraction of the metallic compounds used for such purpose, thus securing an accurate adaptation of the appliance. Where the base plate is swaged, the quality of hardness not being so essential, the choice of materials and methods in ob- taining the impression and model must be determined by the relative contractability of the metals used for dies. Consid- erable expansion of the impression and model would be fairly 164 MECHANICAL DENTISTRY. compensated for by the greater shrinkage of zinc, while a less degree of expansion of the model would be indicated in the use of Babbitt metal, or other similar metallic compounds fusing at a low temperature, and having proportionately less shrinkage. The experiments of Dr. Spence furnish important and valuable data for intelligent discrimination in the selection and treatment of plaster for special conditions, and should be carefully studied by every painstaking operator. A singular and heretofore unobserved phenomenon in con- nection with the setting of plaster mixed with plain water is pointed out by Dr. Bowman Macleod, of Edinburgh,* from which he draws conclusions so practically important concerning its influence in modifying the adaptation of a dental substitute, as well as in other respects, that space is here given to such of his observations as are deemed essential. A block of plaster was cast within a square of two feet, which on the following day showed an expansion of five- sixteenths of an inch in length and breadth. " But I found," he says, "that not only had the plaster expanded, but the upper surface was raised; and on sawing the block through in a diagonal direction, I found that instead of the block lying dead upon the plane beneath, it presented a concave surface toward the plane, the highest point of which measured one- half inch. This showed, first of all, that the plaster had not only expanded, but had done something more than its now greater length and breadth would lead one to suspect; for, in thus taking a concave form, it must have either retracted to an equal extent, or expanded in an irregular manner, causing warpage. " Making still further experiments by casting plaster in the ordinary impression cup, I found, invariably, the same result produced, and that the centre portion—the palatine portion— of the cup always presented an open and well defined space between the upper surface of the impression cup and the lower surface of the hardened plaster. This circumstance, therefore, would produce in your model a fault similar to that resulting from the sucking of the waxy or resinous impression materials, * Transactions of the Odonto-Chirurgical Society. IMPRESSIONS OF THE MOUTH. 105 and, as you can readily see, -would give you a much higher dome than that of the natural arch. Hence the rocking of the plate, which has hitherto been attributed—if my deductions be justified—to every cause but the right one. Continuing my researches, I found that although in the equal surface and depth of the modeling tray, the defect always ran in one direction, yet on pouring the plaster into irregular molds, such as the impression of the mouth, the position of the point of warpage was not always persistent, but seemed to be con- trolled by the thickness of the superincumbent layer of plaster, and this led to the conclusion that while in some instances the defect would determine itself on the palatine ridge in the shape of an exaggerated dome, at other times, and that more frequently in under dentures, it would express itself in irregular lateral expansion, and consequent misfit upon the posterior portion of the alveolar ridge. Naturally, then, I began to inquire how this defect might be overcome, and I find that by the addition, to the water with which the plaster is mixed, of potash alum (hitherto used entirely for the purpose of quick setting in impression taking), in the proportion of from three to four ounces to the gallon, you will entirely overcome the irregular expansion and consequent warping which takes place in coarse plaster-of-Paris as used with water alone. But here you have the two blocks of equal dimensions—one cast with water, and the other with potash-alum water. It requires no explanation on my part to point out the difference between the two. In the one case, the expansion is five-sixteenths of an inch; warpage, one-half inch. In the other, expansion, nil: and warpage, ditto; and the two surfaces, dead. You have here a series of impression cups of various sizes and shapes, filled with plaster, cast with pure or plain water, and with potash alum, and which require but to be examined to con- vince you of the fact of the deadness of plaster-of-Paris when treated with potash alum, and its behavior under ordinary cir- cumstances. The conclusion I draw from this is, that all plaster, either for impression taking or for models, should be cast with potash alum, when strict and definite results are to be obtained; and that in the case of gum block work, that 166 MECHANICAL DENTISTRY. opening of the joints—which has hitherto caused so much trouble to practitioners, and, to a great extent, has prevented the more general adoption its other merits might have com- manded, and which has drawn out many suggestions as to the best mode of prevention—the opening of the joints may now be entirely prevented by the use of potash alum for both matrix and model within the flask." Manner of Obtaining an Impression of the Mouth in Plaster for Partial Upper and Lower Dentures.—In partial cases, whether above or below, there are, almost universally, conditions associ- ated with the presence of the remaining natural teeth which, until more recently, have been thought to contra-indicate the use of plaster as an impression material, but experience has demonstrated that, with the adoption of certain available means, and careful and skillful manipulation, there are few if any cases in which this material may not be successfully employed. Its superior capabilities of receiving a faultless imprint of the mucous surfaces recommend it for this purpose in all suitable cases. The conditions mentioned above relate to those cases where the cervical portions of the crowns are relatively small; or where the teeth are irregularly arranged in the circle, having either an anterior, posterior, or lateral obliquity; or where there are marked depressions or fossas on the external border of the alveolar ridge; and especially where there are well-defined dovetailed or wedge-shaped interdental spaces. These condi- tions prevail in different degrees in individual cases, and the instances are exceedingly rare where some or all of them are not present. As plaster prepared for impressions, in the act of setting or hardening, becomes rigid and unyielding, and therefore practically incapable of any change of form by dis- tortion or dragging of any portion of it on traction, the difficulty, not to say impossibility, of detaching it by the ordi- nary means, where these conditions prevail, will be apparent. In cases of very slight deviation from the normal position of the teeth, sufficient force, judiciously applied, may disengage the impression, provided the plaster is not allowed to set hard. To provide against separation of the plaster and cup on the appli- IMPRESSIONS OF THE MOUTH. 167 cation of the necessary force, the outer edge of the cup (Fig. 62) may be turned in somewhat, or a cup like that shown in Fig. 68, especially designed for the purpose by Dr. Samuel Wardle, may be used. It will be seen to consist of an ordinary tray, the cup portion perforated in the centre, through which a small rod passes with a screw cut on one end, and the other sur- mounted with a concave flange, around and underneath which the plaster collects. The rod is formed with a shoulder resting on the palatal face of the cup, and is fixed in position by screw- ing the tap against the lower surface of the tray. A number of these centre pieces, with shafts of various lengths, should be provided, in order that any desired elevation may be given to the cup or flange; for the latter is designed not only to confine the plaster, but also to carry it up into the roof of the mouth Fig. 68. where the latter is very deep. On removal of the impression from the mouth, if any portion of the plaster essential to the form of the impression should break away, the fragment or fragments may be secured and afterwards applied to the frac- tured surfaces. If, however, the mal-arrangement of the teeth is considerable, or very pronounced, the separation of the plaster impression must be accomplished in some other way than by simple trac- tion. Prof. Charles J. Essig recommends the following method of procedure:— " An impression cup should first be selected, of the proper size and shape — those with the flat floor (Fig. 62) are best for partial cases ; the plaster should be mixed thin, almost as thin • 168 MECHANICAL DENTISTRY. as water, adding chloride of soda to facilitate setting. Plaster mixed in this manner does not become as hard and unyielding as that mixed merely to saturation. Now oil the cup so that it will readily separate from the impression when hard, fill the cup as soon as the plaster thickens sufficiently, then, with a small spatula place a layer of the soft plaster in upon the palatine surface, otherwise by enclosing the air in the deep portion of the arch, the accuracy of the impression may be impaired. After this precaution, the cup is placed in the mouth, and gently pressed up until its floor comes in contact with the teeth. When the plaster is sufficiently hardened, remove the cup, which, from its having been oiled, is done without difficulty; with the thumb and index finger break off the outside walls; the portion covering the palatine surface is then removed by the use of a blunt steel spatula, curved at the end in the form of a hook. The pieces are then placed back into the cup, where they will be found to articulate with perfect accuracy. " Should the first attempt be rendered futile, by the tendency to nausea, or troublesome gagging on the part of the patient, camphor water, as recommended by Dr. Louis Jack, may be used as a gargle, which will, in nearly every case, prove an effectual remedy." This device is effectual to the extent described by Prof. Essig, but it affords only a partial remedy for difficulties which present themselves in many of these cases. The most for- midable obstacle to the removal of a plaster impression will be found generally in that portion of it embraced in wedge-shaped interdental spaces, and undercuts formed by truncated, cone- shaped crowns, and malpositions of the teeth, and when the outside walls of the impression alone are broken off, and re- maining portions are imbedded in these undercuts, it will rarely be possible to remove the portion covering the palatal surface without further fracture, and removal by sections. It is to be regretted that Prof. Essig has not given his method of operating in such cases more fully and explicitly. The following mode of operating,, in which gutta-percha cups are used, was practiced by the late Prof. Austen, and is highly commended by the editor of the last edition of Harris' work: IMPRESSIONS OF THE MOUTH. 169 " Take a wax impression and make a model; in partial cases, brush over the teeth of the model one or two layers of thin plaster, to fill up all undercuts, and to make the plate fit loosely ; saturate the model with water, and mold over it a gutta-percha cup. This last is done, not by using the gutta- percha in sheet, but by first making it into a ball; then work- ing it from the palate outward, leaving a thick mass in the centre. It should be, on the inside, from one-fourth to one-half of an inch thick, so as to be stiff and unyielding, but on the outside not more than one-eighth or one-sixteenth thick, so as to be slightly elastic and yielding. The whole inside of the cup must be roughened up with a scaler or excavator, in such a way that the plaster can take firm hold. In most partial cases, the impression will have to be removed in sections; the inside remaining entire, but the outside and the parts between the teeth coming away separately. In certain cases it is necessary to partially cut through the cup before putting in the plaster, and usually upon the thick masses of gum which fill the interdental spaces. A cut on the inside, in line with the ridge, gives pliancy to an otherwise rigid cup, and permits its easy removal. When it is desirable to extend the cup around the entire arch, so as to get an exact plaster impression, not only of the gum but of all the remaining teeth, this rim of gutta- percha must be slit at two or three points, to give that pliancy which is a chief merit in this form of cup. These cups have no handle, but are removed by inserting a plugging instru- ment into a small hole previously made in the back part of the cup, where it is thickest." The following novel and original method of securing an un- broken plaster impression in cases requiring the replacement of the front teeth is thus described by Dr. Stewart J. Spence, in the March number (1883) of the Dental Cosmos:— " In replacing one or more of the six anterior teeth of either arch it is frequently desirable to provide for the retention of the plate by bracing it against the palatal or lingual surfaces of the bicuspids or molars, by the application of ' stays ' fitted to these surfaces, with just sufficient pressure to retain the denture and not enough to move the teeth. 170 MECHANICAL DENTISTRY. " It is the more desirable to employ this principle of reten- tion in those cases where the surfaces referred to bulge or lean inward, so as to lock the plate in position. But it is precisely in such cases that there arises the difficulty of taking an un- broken and correct impression by the ordinary impression trays, the remedy for which difficulty is the subject of this article. " The tray, and manner of using it, which I am about to de- scribe, are, I believe, exceedingly well adapted to overcome the difficulties in the cases referred to. Not only do I obtain a cor- rect impression of the teeth at the parts desired, but also an unbroken impression of the palatal arch. " I will first describe the tray, and how I make it; and then my mode of using it. It can readily be made in a few minutes, out of an ordinary upper tray, with a pair of shears. I cut away about one inch of the posterior portion of the tray, and thus bring it within the dimension most needed for taking im- pressions for small partial plates replacing anterior teeth. Next cut away from each side the flange of the tray, leaving it re- maining in front. Then cut through the tray from the centre of the posterior palatal part forward to the base of the remaining flange in front, which is left unsevered; this presents two wings, as we may term them. Three objects are gained by dividing the palatal portion of the tray into these two wings: First, the wings can be bent laterally to the width of the arch of each mouth, measuring from bicuspid to bicuspid, across the oral cavity. Second, they can be readily bent upward or downward to suit any height of palatal arch. Third, the plaster runs through the space between the wings, and anchors the impres- sion to the tray, so that they sustain the strong force required in removing the impression from the mouth without separating from each other. " The tray being completed we will describe its use. Plaster is mixed with pulverized alum, to produce hardness in a short time, and at the same time to prevent expansion of the plaster. I mix it only moderately thick and do not stir it long, because I have found, by experiments, that this yields the hardest cast with the least expansion. It is then placed in the mouth, the plaster, as a rule, not being permitted to extend any further IMPRESSIONS OF THE MOUTH. 171 beyond the bicuspids than can be avoided. To insure a correct impression of the higher parts of the roof, when needed, the fingers should be inserted to the back of the tray and the plaster there pressed against the palate. It will readily be seen that by not investing the buccal surfaces of the bicuspids the impres- sion may be more easily withdrawn; but this is but one object for cutting away the side flanges of the cup—the main reason for so doing is that the outer cusps of the bicuspids and molars may be exposed, so that they may be grasped by the finger. Therefore, before the plaster has fully hardened, I trim away any of it which may have run over these outer cusps and then give time for the impression to become very hard. This being done, I place the index finger under the cusps, and forcibly draw these teeth outward from their positions in the arch ; thick rubber dam being wrapped around the finger. This application of force will usually so far move the teeth on which it is employed, in twenty or thirty seconds, that force may safely be used at the handle of the tray—this, however, should never be applied until the plaster has set quite hard; for it is a fact, though not generally appreciated, I believe, that pressure made on plaster, even when apparently set, will compress or dislodge its par- ticles similarly, except in degree, to that which is done by pres- sure on wax or modeling composition: the ease with which a piece of plaster can be crushed between the thumb and finger after it has set sufficiently to break with a sharp fracture is de- monstration of this fact. Both hands of the operator should be used to spread the teeth if an assistant is at hand to manipulate the tray. " Interrupted traction is the best way in which to apply force to the handle: but the motion each way must be very slight, a mere wriggle, not a swaying up and down, or the plaster will be broken in the interdental spaces. The force exerted in thus withdrawing the impression also aids in spreading the teeth if the plaster has been permitted to set sufficiently hard. If, when it has been partially -withdrawn, the impression be per- mitted to remain a minute or two, it will be more easily re- moved at the end of that time, because it has been pressing the teeth in the meantime. 172 MECHANICAL DENTISTRY. " The same tray and mode of use apply to either arch. Of course the surfaces of the teeth should be free from salivary calculus." While the method above described is doubtless practicable in a limited number of cases, and could be made available in the construction of a substitute sufficiently yielding and elastic to .pass between the teeth on the application of moderate force, there are manifest objections to such means of retention in the cases spoken of by the writer whenever the plate or base is com- paratively rigid and inelastic. To utilize the principle involved, namely, the mechanical support afforded by the teeth as a means of retention, the coaptation of the substitute to the undercut surfaces must be as perfect as that of the impression. In the case of rigid bases, very nearly if not quite the same difficulty of applying and removing the substitute must obtain Fig. 69. A A, Teeth or interspace. B, Wax impression tray. C, Plaster impression of palatine vault and palatine half of teeth or interspace. D D, Buccal or labial half of teeth or interspace. E, Palatal vault. as that experienced in the removal of the impression. It may be reasonably supposed that the patient would be unable to apply a force equal to that implied when Dr. Spence says " both hands of the operator should be used to spread the teeth if an assistant is at hand to manipulate the handle of the tray." And if the removal of the piece by the patient, on the applica- tion of adequate force, were possible, the frequent and prolonged repetition of the act, absolutely necessary in all such cases, would ultimately loosen and displace the teeth used as supports, and thus defeat the object of the operator. The author is indebted to Prof. Wilbur F. Litch for the following description and illustration (Fig. 69) of a method of securing plaster impressions for partial cases :— IMPRESSIONS OF THE MOUTH. 173 " A wax impression tray is made, and either scored or per- forated, to afford anchorage for the plaster. This extends only midway of teeth or interspace. After the plaster has hardened, the outer edge is trimmed, notched, and oiled in the mouth, and sections D D of the diagram made by carrying plaster into position by means of a spatula, the outer section being made in two pieces, joined at about the median line. The three pieces are removed separately and joined by means of the notches made in the palatine section, C, into which notches the plaster of sections D D will fit. After the three sections are cemented together, they may be imbedded in plaster, to more securely hold them together while the model is being poured." Another method of securing plaster impressions in sections is the following, practiced by Dr. A. G. Bennett, Clinical Instructor in the Pennsylvania College of Dental Surgery : — A A, Molar teeth. B, Palatine vault. C C C, Impression tray. D D, Wax cut-ofls. E E, Labial sections of plaster impression. F, Palatal section of impression. "A wax cut-off is placed in the floor of the impression tray in such manner that it will touch the crowns of the molars and the cutting edges of the incisors about midway between their buccal or labial and palatine walls, as shown in Fig. 70, letters D D. After the wax cut-offs have been firmly attached to the tray by heat, the tray is oiled, filled with plaster, and placed in position in the mouth. After the plaster has hardened, the tray is withdrawn, the plaster remaining in the-mouth, when the outer sections, E E, are readily broken off, and the plaster section, F, withdrawn. The several pieces are then replaced in their proper position in the tray." Dr. F. M. Dixon, of Philadelphia, Pa., gives the following description of a method of procedure in the class of cases under 174 MECHANICAL DENTISTRY. consideration, which seems to provide more perfectly for the removal of the palatal portion of the impression in cases characterized by unusual inward inclination of the teeth. The process described relates to partial upper cases:— " First take an impression of the whole upper jaw in wax, and harden by applying ice-water. Divide this impression, with a slightly heated knife blade, into the number of sections desired for the plaster impression. From the inner surfaces of these sections, a sufficient quantity of the wax is cut away to make room for the required amount of plaster. Hard-setting plaster is then poured into one of the palatal sections, and the latter placed in its proper position in the mouth, securing an im- pression of the palatal surfaces of the teeth of that side, and about one-third of the palate of the same side. When the plaster has hardened sufficiently, the section is removed and laid to one side while an impression of the opposite side is secured in the same manner. " The patient may now be dismissed with an appointment for another sitting. In the interim, these sections are carefully trimmed in such a manner that the lower or lingual surface shall present a bevel from margins near the mesial line of the palate to the grinding surfaces of the teeth, that the next section may be readily removed after hardening in the mouth. When the patient returns, the prepared lateral sections, oiled on their under surfaces, are placed in the mouth and an impression of the central portion of the palate and palatal surfaces of the incisors are secured, as before. The impression of the buccal surfaces, when needed, are taken in like manner, with the other sections in situ." While the author fully recognizes, in these partial cases, the value and importance of absolute accuracy, so far as it relates to impressions of all the parts affording a basis for the sub- stitute, he believes that the paramount necessity, claimed by many, of securing an equally exact impression of all undercuts has been over-estimated. A partial denture constructed from any substance capable of being molded accurately to a model obtained from such an impression, especially as it relates to cone-shaped interdental spaces, is incapable, in that condition, of IMPRESSIONS OF THE MOUTH. 175 being forced into place in the mouth, and not until considerable, if not all, of such parts as the operator has been to so much pains in securing with faultless accuracy has been removed, is this possible. We do not wish to be understood as advising against the use of plaster in these cases. It has important and indispensable uses in this connection, but should be employed with intelligent discrimination, and, in view of the unusual difficulties attending its successful manipulation, only in cases of plain and positive necessity. We believe that, in all cases not characterized by excessive undercutting, either gutta-percha or the modeling compound will, with careful manipulation, secure sufficiently accurate results, but when these conditions are more pronounced, the danger of distorting the body of the impression on the application of sufficient force to detach these materials from interdental and other undercut spaces, would point to the use of plaster as the more suitable material, not so much to obtain a perfect impression of all the parts in their existing relations to each other, as to secure exemption from any change of form in the general body of the impression. In such cases, the use of plaster is clearly indicated. Manner of Obtaining an Impression of the Mouth in Plaster for Entire Upper Dentures.—The form of cup used in securing an impression of the upper jaw for entire sets of teeth, differs in no essential respect from that recommended when wax is used for similar purposes. If the external border of the alveolar ridge is very deep, or there is considerable space intervening between the heel of the cup and the floor of the palate, a rim of wax may be placed along the outer margin of the cup, and extended across its posterior border, in order more effectually to confine the plaster within the cup and prevent its escape into the back part of the mouth before it has fairly reached the palatal vault. If the latter is very deep, with a marked excavation in its central and anterior portion, or if it presents somewhat the form of a deep fissure, the plaster may fail to be carried perfectly against the floor of the palate, or the air becoming confined within the central portion of the arch, when the plaster is pressed up, may displace the latter and form corresponding chambers in the impression. If these 176 MECHANICAL DENTISTRY. imperfections are but slight, they may be subsequently reme- died either by filling up the cavity or cavities in the im- pression, or by trimming away at these points from the model. The better plan, however, where these conditions of the vault prevail, is to take up a small portion of plaster on the end of a spatula and apply it to the deeper portions of the arch just before introducing the cup. In preparing plaster for use in these cases, it should be so treated as to insure quick-setting when applied to the mouth. This is generally accomplished either by adding to a very thin mixture of plaster and water a small quantity of sodium chloride or common salt, and stirring until it begins to thicken; or by constant and protracted beating with a spatula until somewhat tough and pasty. In either condition, it adapts itself readily to the parts, hardens quickly, and is not liable, with ordinary care, to incommode the patient by running back too far upon the soft palate, or into the fauces. So quickly, indeed, does it condense, that unless expeditiously introduced into the mouth, it will begin to "set" before the parts are fairly imbedded. When preparing it for use, therefore, the plaster should be mixed at the chair with the cup conveniently at hand, while the patient should be in proper position and in immediate readiness for the operation. In view of the liability of the plaster to run back into the fauces when the cup is pressed to its place in the mouth, pro- ducing nausea and involuntary retching, and which is very liable to occur whenever the mixture is too thin or is im- properly manipulated, it is recommended to instruct the patient to avoid swallowing while the plaster is in the mouth. Patients are also advised to breathe through the nostrils, but we see no good reason for this injunction. It should be remembered that, in the act of breathing through the nose, the velum palati or soft palate is depressed to cut off the passage of air through the mouth, and that it is thus brought more immediately in con- tact with any portions of plaster that may be protruding from the heel of the cup. The stimulus of contact will tend to pro- duce involuntary contractions of the muscles of the soft palate and fauces, and thus portions of soft, or fragments of hard, plaster will be worked or drawn back into the fauces, producing IMPRESSIONS OF THE MOUTH. 177 the very evils it is designed to avoid. If, therefore, patients are instructed at all in this respect, they should be advised to breathe naturally through the mouth, this channel affording less ob- struction to respiration than that through the nostrils, in the act of taking an impression. The patient being seated as nearly upright in the chair as possible, with the head inclined slightly forward, the cup is filled with the plaster mixture and introduced quickly into the mouth, when it is pressed up slowly and gently until the parts are completely encased and portions of plaster are seen to protrude from all parts of the margins of the cup, other-wise the impression is liable to be imperfect, either on its outer borders or on its posterior palatal face. Immediately after introducing and pressing up the cup, the lip in front should be extended and drawn down over the cup, when gentle pres- sure, as the plaster is hardening, may be made upon the lip and cheeks, to force the plaster more perfectly into close contact with the outer surface of the alveolar ridge. It is essential to perfect success in this operation that the cup, after the parts are once imbedded, should be held perfectly stationary until the plaster becomes fixed, as the slightest movement when the plaster is in the act of consolidating will derange the impression and render it faulty. Again, if after the parts are imbedded, the operator discovers that they are not sufficiently encased, and the plaster has partially set, no further effort should be made to press the plaster up upon the parts, but the cup should be withdrawn and the operation repeated with fresh plaster. If the operation has been successfully conducted, the plaster will adhere to the mouth, in most instances, with great tenacity, and it will be necessary to observe some caution in removing it, for, if forcibly detached, injury may be inflicted upon the soft parts by tearing away portions of mucous membrane; or the impression may be fractured or otherwise impaired. In addition to the means already adverted to in connection with the method of separating wax impressions from the mouth, resort is sometimes had to the following expedient: The central portion of the cup being pierced with two or three small holes, 12 178 MECHANICAL DENTISTRY. a blunt-pointed probe is passed at these points through the plaster, before the latter has hardened perfectly, to the roof of the mouth. Into these passages the external air passes and diffuses itself between the surface of the plaster and the palate, when the impression may be readily detached. The author has succeeded best in detaching impressions in such cases by upward and interrupted traction upon the handle of the cup, which, by depressing the latter posteriorly, more readily permits the introduction of air than by either of the methods commonly employed. Manner of Obtaining an Impression of the Mouth in Plaster for Entire Lower Dentures.—The general form of cup used for the above purpose is shown in Fig. 71. This being filled with the plaster mixture, prepared as described in connection with full upper pieces, is inverted and quickly introduced into the mouth Fig. 71. Fig. 72. and pressed down upon the ridge until the latter is completely imbedded, being careful at the same time to draw7 the lower lip away from the cup, and the cheeks outward, in order to prevent any loose tissues from folding in upon the outer borders of the ridge as the cup is pressed to place, thus seriously marring the impression. In securing an impression of the lower ridge in plaster, better results can, in many cases, be obtained by first taking the im- pression in wax, enlarging the impression thus secured with suitable instruments, and using this as a tray for plaster. A form of tray, contrived expressly for the use of plaster by Dr. B. W. Franklin, is exhibited in Fig. 72. It consists of two chambers, or a double groove, communicating with each other by a fissure running from heel to heel of the cup. The groove corresponding with the curvature of the lower jaw is filled with IMPRESSIONS OF THE MOUTH. 179 plaster properly prepared, inverted, passed into the mouth, and pressed down upon the parts. As the cup is pressed down, portions of plaster will be forced through the fissure into the upper chamber; this should be pressed down at all points along the groove with the finger, securing more perfectly, in this manner, the intrusion of the plaster into any irregularities or depressions that may occur in the ridge. Or, the empty cup may be placed in its proper position over the jaw and the plaster introduced into the upper groove and pressed down with the fingers through the fissure on to the ridge, filling the depending chamber. CHAPTER III. PLASTER MODELS. After an impression of the mouth has been secured in either of the ways mentioned in the preceding chapter, the next step in the process of constructing an artificial denture is to procure from the impression a representation of the parts in plaster. The copy thus secured is called a model, and, if correctly obtained, is a true counterpart or fac-simile of all parts of the mouth represented in the impression. Manner of Obtaining a Plaster Model from an Impression in Wax, Gutta-Percha, or Modeling Compound, for Partial Dentures.— The impression should be first trimmed by cutting away super- fluous portions that overhang the borders of the cup, care being taken not to mar any essential part of the impression. The surface imprinted should then be uniformly smeared with a thin coating of oil applied with a camel's-hair brush. The oil should not be of too thick a consistence, nor applied in too large quantities, as it will collect in the more depending portions of the impression, and, failing to be displaced by the plaster, leave the model imperfect at these points, especially at the coronal extremities of the plaster teeth. The cup is now surrounded by some substance that will confine the plaster and give proper form to the body of the model. For this purpose an}T material that is easily shaped may be used, as a thin sheet of lead or wax, paper, strips of oil or wax cloth, etc. Before pouring the plaster, if it is desired to strengthen any of the plaster teeth—as those adjoining the vacuities in the jaw, or such as are to be used in adjusting clasps—and thus secure them against accident in handling, adequate support may be imparted to them by placing short pieces of stiff wire vertically in the depressions made in the impression by the teeth, supporting them in an upright position by imbedding one end in the wax or other material in the centre of the bottom of each cavity. 180 PLASTER MODELS. 181 When the cup is properly inclosed, a batter of plaster, of some- what thinner consistence than that used for impressions, is poured in upon the surface of the wax in sufficient quantity to give to the body of the model a depth of from one to three inches, according to the particular requirements of the case. The plaster should not be poured directly or hastily into the cavities formed by the teeth, but upon points contiguous to them, and from which it should be allowed to run slowly into the depressions, expelling the contained oil or air, and filling them perfectly. When the plaster has become sufficiently hard, any portions overlapping the borders of the impression, and not essential to the form of the model, should be cut away, and the two separated by immersion in warm water until the warmth imparted to the model renders the impression sufficiently soft to allow the former to be removed without fracturing the plaster teeth. Dry heat should be applied to the model whenever it is desired to obtain duplicate copies from the same impression, as by the use of hot water the impression is destroyed, the latter, however, being generally used when gutta-percha is employed. When separated from the impression, the model should be properly trimmed and shaped with a knife blade. The general form of the body of a model is shown in Fig. 74. Where a swaged base is required, the walls, as will be seen, are made as nearly vertical or parallel as will admit of the model being readily detached from the sand in the process of molding; for if made too flaring or divergent, the metallic die obtained from it will be more liable to crack or spread apart under the repeated strokes of a heavy hammer, or to rock under one-sided blows. During the process of stamping or forcing a metallic base into adaptation to the die—which is a metallic counterpart of the model—the plate, when cut to the exact pattern of the parts to be covered by it, is frequently forced or dragged back toward the heel of the die, and is thus drawn from the teeth at the sides and in front. This displacement of the plate may be prevented by cutting away all of the plaster teeth from the model, leaving, however, enough of them remaining where they unite with the body of the model to form a shoulder to 182 MECHANICAL DENTISTRY. Fig. 73. each tooth, as in Fig. 73. In this case the plate should be sufficiently ample in its dimensions to partially overlap the border, when, as it is forced into adaptation, distinct in- dentations will be made in it, corres- ponding exactly with the palatal curvatures of the teeth; the portions of the plate covering the cut ends of the teeth are then cut away with plate forceps or other instruments. If, however, the plate is of the exact size required before stamping, one or two plaster teeth upon each side of the model may be allowed to remain, against the anterior face of which the plate is made to rest, holding it stationary. Fig. 74. Fig. 75. Manner of Obtaining a Plaster Model from an Impression in Wax, Gutta-percha, or Modeling Compound, for Entire Dentures.— The same general method is pursued in obtaining a plaster model from an impression of either the upper or lower jaw for entire dentures with the substances mentioned, as that employed in partial cases. The general form of these pieces is represented in Figs. 74 and 75. If it is desired to swage a rim to the plate, forming a groove ^ or socket into which the plate extremities of the teeth are ^ received, the model should be formed in the manner represented in the annexed cuts; in which it will be seen that an abbrpt shoulder is formed on the external border of the model of the PLASTER MODELS. 183 upper jaw (Fig. 74), but which on the lower (Fig. 75), is extended round the inner border also, as it is desirable, in the latter case. to give a rounded edge to the lingual border of the plate, and which is accomplished in part by swaging in the first instance and afterwards by turning the edge down upon the plate with pliers or by other means. The model is prepared by adjusting a strip of softened wax around the border and cutting away from its upper surface in such a way as to form a groove, the bottom of which shall be on a line with the extreme edge of the base or plate, and which should be indicated upon the model with a pencil mark before applying the roll of wax. Plaster may be substituted for wax, and should always be used whenever heat is applied to the model in the process of obtaining a metallic swage, as by the "dipping" method. If the model is to be used in molding, the groove should be sufficiently open to permit the ready withdrawal of the sand, otherwise the die at this part will be imperfect; if, however, the face of the model is to be immersed in molten metal, securing first the counter-die, any form may be given to the groove that will best facilitate the operation of overturning the margins of the plate. Rimmed plates are only required when single gum teeth or sectional or entire blocks are employed, or when plate teeth are mounted on a platinum base with continuous gum. Whenever an air chamber is to be stamped in the base, the model should be prepared for the purpose before casting the metallic swages. The general form and position of the central cavity or chamber in the arch is represented in Fig. 74. The model maybe prepared in either the following ways: 1. The form of the chamber may be cut from the wax or plaster impression, in which case the plaster will be raised at a corresponding point or points upon the model, and will have exactly the same form and depth as the cavity in the impression. 2. Cover the palatal face of the model with a sheet of wax equal in thickness to the required depth of the chamber, and cut out from this, at the desired point, the form of the cavity; fill the latter with plaster, and when hard remove the wrax 184 MECHANICAL DENTISTRY. and trim the raised portion to the proper form. 3. Cut a pat- tern chamber, of the required form and thickness, from sheet wax or lead ; place it in proper position in the arch and press down with the fingers or burnisher until it conforms to the contour of the palate; it is then fixed in place either by con- fining it with a small piece of wire or tack driven through it into the plaster, or by interposing softened wax or other adhe- sive material between the chamber and model. A small brush loaded with a varnish mixture passed round the edge of the chamber will insure sufficient adhesion of the latter. The same general method as that when central chambers are formed is pursued in the preparation of the model when it is desired to construct lateral cavities in the plate. The form and position of these on the model will be indicated by inspec- tion of the form of " lateral cavity " plates as exhibited in the chapter on " Entire Dentures. " There are other modifications in the form of cavity plates, some of which are obsolete; that known as " Cleveland's chamber" is still in limited use, and will be described in a subsequent chapter, but does not require a model differing in form from the one described in connection with full dentures with central chambers. Manner of Obtaining a Plaster Model from an Impression in Plaster, for Partial Dentures.—The surface of the impression in plaster should first be glazed, by applying to it, with a camel's- hair brush, a uniform coating of varnish, to prevent adhesion of the model. Two kinds of varnish are in common use— a transparent and colored. The former is preferred, for the reason that it penetrates the plaster more thoroughly, giving to it a greater depth of surface hardness, while the latter, if not sufficiently fluid, forms a somewhat superficial incrustation, which is liable to peel off in handling, leaving portions of the model unprotected. Either, however, if properly prepared and applied, may be employed. Formula No. 1. Formula No. 2. TRANSPARENT VARNISH. COLORED VARNISH. Gum sandarach, . . . 5 oz. Gum shellac,.....5 oz. Alcohol,.......1 quart. Alcohol,.......1 quart. PLASTER MODELS. 185 The sandarach and shellac should first be freed from all impurities by careful picking and washing; they are then added to the alcohol and digested over a moderate heat until thoroughly dissolved. Other substances, as gum elemi, Venice turpentine, etc., have been recommended as addi- tional ingredients, but they are not indispensable, and may be omitted without sensibly impairing the properties of the varnish. After glazing the surface of the plaster impression with varnish, a thin and uniform coat of oil should be applied; it is then enveloped, and the model procured in the same manner as when the other plastic materials are used. The following method of preparing the plaster impression before it is filled in for the model is recommended by Dr. C. W. Spalding: " After the impression has become hard, coat the surface with a lather of soap and water; wash this off and immerse the model in water. This expels air and avoids liability to porosity of the surface of the model. Again coat the surface with a strong lather of soap and water, and wash off as before, when the impression is ready to receive the plaster for the model. I prefer this method to varnishing, for the reason that the varnish used is not always of uniform consistence." In separating the model from a plaster impression, for par- tial cases, it will be necessary to cut the latter away in pieces, as any attempt to separate the two in the ordinary manner would inevitably break away the plaster teeth from the model. The impression should be chipped away with care, to avoid defacing the model. To provide more perfectly against this accident, it is better to coat the impression with colored var- nish, as this will indicate with greater certainty the line of contact or union between the two pieces. Dr. Spalding sug- gests a simple and effective device for the same purpose, which consists in coloring the water used to mix the plaster for the impression with aniline red. When separated, the model should be trimmed and formed in the manner before de- scribed. 186 MECHANICAL DENTISTRY. Manner of Obtaining a Plaster Model from an Impression in Plaster, for Entire Dentures.—The preparation of a plaster impression of either the upper or lower jaw, for full dentures, and the method of procuring a model therefrom, differ in no essential respect, except in the mode of separation, from the manipulations required when the impressions have been taken in plaster for partial pieces. A model can, ordinarily, where there are no considerable depressions or undercuts on the ex- ternal face of the ridge, be readily separated, either by taking the model in the hand and tapping the handle of the cup, or by. forcing a wedge-shaped instrument between the impression and model at the posterior border. When, however, there are con- siderable undercuts, such as usually prevail on either side of the median line in front, above and below, or the anterior and middle portions of the ridge are thin, prominent, and over- hanging, the application of sufficient force to detach the im- pression in a body will inevitably fracture such portions of the ridge of the model as are engaged in the contracted spaces. In such cases, the cup being removed from the impression, the latter should be grooved as deeply as possible without marring the face of the model, in such a way that, when the instrument is forced in at suitable points, the impression will be fractured on a line with the grooves, and thus be detached in sections. One groove may be made continuously along a line correspond- ing with the summit of the ridge, and others extending at right angles with this to the outer borders of the impression. When these external sections are removed separately by wedging at the extreme border of the impression, the whole central portion will be easily detached. Extreme thinness and prominence of the ridge will most generally be found in connection with the lower jaw, and will require cautious manipulation to avoid accident to the model. If any portion of the model is defaced by the introduction of the wedge, it maybe afterwards remedied by restoring the contour with plaster. After detaching the model in the manner mentioned, the entire body of it should be glazed and hardened by applying to it a uniform coat of varnish, if it is to be used in obtaining a metallic die. This PLASTER MODELS. 187 protective covering will prevent the surface from wearing, render it more pleasant to the touch, facilitate its withdrawal from the sand, and give a more perfect mold. A model may be better prepared for permanent preservation by immersing it for a short time in a solution of carbonate of soda, by which its surface is converted into carbonate of lime, and thereby rendered hard and durable; care must be taken not to introduce any of the bicarbonate of soda into the solution. CHAPTER IV. METALLIC DIES AND COUNTER-DIES. A metallic die is a fac simile or transcript of the mouth in metal, and is also a copy or likeness of the plaster model. A metallic counter-die is a copy of the impression, and is a reversed image of the die and plaster model. Manner of Obtaining a Metallic Die.—Two general methods are employed in procuring a metallic counterpart of the model; first, by molding; secondly, by a process termed " dipping." Molding.—For this purpose the best material is marble-dust, though other substances, as sand, Spanish whiting etc., have been recommended. Marble-dust has the advantage of being always ready for use, as it absorbs sufficient moisture from the atmosphere to render it cohesive, is cleanly, and gives a smooth and uniform surface to the die. When sand is used it should be fine and even-grained, the best for the purpose being that used by brass founders. It is prepared by mixing with it sufficient water to render its particles somewhat adhe- rent, so that when portions of it are pressed in the hand and then parted with the fingers it will break away in well-defined fragments. Excess of water should be avoided, as the vapor formed by the molten metal, when poured upon it, will displace portions of the latter, and form cavities, or blisters, in the face of the die; nor should the sand used be too dry, as in that case it wull crumble away in detaching the model. Oil has been proposed as a substitute for water, in which case it is recommended to add one quart of the former to a peck of sand. It is claimed that the sand so prepared is always in immediate readiness for use. The molding material being properly prepared, the model is placed with its face uppermost on the molding board, and surrounded with a metallic ring. A common " wagon box," of which two or three sizes should be had, will answer every purpose. If sand is used it should first be well sifted, to 188 METALLIC dies and counter-dies. 189 remove the coarser particles, and then filled into the ring, packing it closely with the fingers around and over the model until even with the upper edge of the box. Some care must be observed in the management of the molding material when packing it, for, if made too compact, the vapor formed in pouring hot metal, failing to pass out readily, will be confined within the cavity and cause imperfections in the face of the die; or, if too loosely packed, the fluid metal, when poured into the mold, will, to some extent, permeate the pores of the sand or other material and render the face of the die rough and imperfect. The box, with the model encased, is then lifted above the board and the model dislodged by tapping it gently underneath with a small mallet or hammer until it parts from the mold. The uncertain and hazardous method, sometimes resorted to, of detaching the model by pressing it alternately backward and forward until loosened, and then lifting it out, should never be practiced, as more or less deformity of the mold is unavoidably produced thereby. It not unfrequently happens that the ridge on the plaster model of the upper jaw overhangs, forming corresponding depressions above, the excavations occurring more commonly in front and on each side of the mesial line. Whenever this form of the model exists, it will be impracticable to obtain a correct mold in the manner just described, since the sand becoming impacted in these excavations will be broken away and remain with the model when the latter is dislodged. The difficulty mentioned, however, may be readily overcome in all cases by employing the sectional molding flask invented 1 >y Dr. G. W. Hawes, the several parts of which are represented in the accompanying cuts. Fig. 70 represents the lower ring, composed of three movable pieces, with flange extensions that project in toward the centre. When used, this portion of the flask is closed and the sections kept in place by pins passing through the joints. Inside of this ring the model is placed face upward, the ridge extending a little above the upper plane of the ring. Sand, well sifted, is then packed in around the model on a level "with 190 MECHANICAL DENTISTRY. the most projecting points on the outside of the ridge, as indi- cated by the dotted line in Fig. 78. The surface of the sand should be trimmed smoothly, and should be cut squarely and at right angles wdth the ridge to prevent the sand from breaking away when the model is withdrawn. Very finely pulverized charcoal, contained in a loose muslin bag, is now sifted over the exposed surface of the sand to prevent the next portion contained in the upper ring from adhering. The plain ring (Fig. 77) is then placed over the one containing the model, and is filled with sand well packed over the face of the die. The upper ring is now carefully lifted from the lower one on a Fig. 76. Fig. 77. Fig. 78. line with the pins, thus separating the two portions of sand, and again exposing the uncovered face of the model. One of the pins should then be drawn from the lower ring, the sections of the latter carefully unfolded, and the model withdrawn ; when the ring may be again closed and confined by replacing the pin. The upper ring is then readjusted in its proper re- lation to the lower one, and the flask inverted, when the mold, if the process has been accurately conducted, will be found perfect. In the absence of the " Hawes " flask, the same results may be attained by employing the following simple method, recom- METALLIC DIES AND COUNTER-DIES. 191 mended by Dr. Bernard, and subsequently described as follows: " The plaster model being prepared in the usual manner for molding, varnish the front (or the whole) with a thin solution of shellac. When dry, apply a mixture of plaster of proper consistence to the front of the model, from the bottom up to the edge of the alveolar line, spreading it on both sides so as to entirely fill up the depression around, making the bottom half an inch thick, and sloping off toward the alveolar ridge. A\ nen this has hardened, separate it from the model, and draw the top of it over sand paper to obtain a flat edge, and let it dry. Readjust this front piece to the model; procure a mold in sand or other material, in the usual way; place the extra piece back in its proper position in the mold, and proceed to cast for the die." In obtaining a mold from the model of a lower jaw, but little difficulty will ordinarily be experienced in obtaining it perfect in the manner first described. The depressions at the posterior and inner border of the ridge are the points most liable to drag or displace the sand, and when the latter occurs, the surplus metal in the die at such points must be cut away with suitable instruments; or the cavities in the model may be so filled out with wax before molding as to permit the ready separation of the model without displacing the sand, in which case, also, it will be necessary, afterward, to trim the redundant metal from the die. A die is more readily and accurately obtained from a model for partial dentures by cutting away the plaster teeth, as before described. The displacement of sand where the ridge over- hangs will, as a general thing, be unimportant in these cases, as the base but rarely more than partially overlaps the border. When whiting or marble-dust is used in molding, it is un- necessary to mix water with them, as the moisture which they absorb from the atmosphere will give to them the proper consistence. Having obtained a mold in either of the ways mentioned, the metal designed for the die should be melted and poured carefully in upon the more prominent portions on the face of the former. If the metal is raised much above its fusing point, 192 MECHANICAL DENTISTRY. or the sand is quite damp, the former should be poured very slowly into the mold. It is better, however, that the sand should be partially dried before pouring the metal, and the die cast on the instant of the metal becoming sufficiently fluid. An observance of these precautions will protect the sand from the over-action of heat, prevent ebullition of the fused metal from the too rapid decomposition of the water of the sand, and will give a smoother face to the die, and secure the metal or metals from undue waste by oxidation. The opinion is enter- tained by some that greater shrinkage of the die occurs when the metallic substance of which it is composed is poured at a temperature much above its fusing point; the fallacy of this is made obvious by a moment's reflection, as a simple example will show that any change affecting the face of the die, as a consequence of contraction, can only occur in the metal between its point of solidification or liquefaction—for they are iden- tical—and its working temperature. Zinc, for example, melts at 773°. Now if its temperature be raised to 1200°, it will re- main fluid until it reaches 773°, and in passing through the intermediate degrees of heat, it will, in obedience to gravity, adapt itself perfectly to all parts of the more depending portions of the mold; and this perfect continuity of the two surfaces will remain unaffected by the contraction of the metal until the latter commences to " set," or solidify (773°), after which, and not until then, the zinc begins to part from the face of the mold by contracting upon itself between 773° and the mean temperature of the air. So far as any change, by contraction, in the face of the die is concerned, therefore, it is obviously immaterial whether the zinc be poured on the instant of melting or at 1200°; the result will be the same in either case. The author is indebted to Dr. B. W. Franklin for the fol- lowing method of securing metallic dies and counters by a process which greatly facilitates the operation and insures accu- rate and satisfactory results: " I take all impressions, full and partial, in plaster. A small hole, less than TV of an inch, is drilled through the highest point of the palatal surface of the impression, through cup and all; into this place two or three broom splints, cutting them off even with the surface of the METALLIC DIES AND COUNTER-DIES. 193 plaster, to allow7 any vapors to pass off. I sometimes smoke the surface of the impression. Around the impression place sufficient putty to form a ring the size and height required for the die. Into this pour, at as low heat as is consistent with the mobility required for sharp castings, the bismuth alloy known as Sir Isaac Newton metal, or, which is better in some respects, 8 parts bismuth and 4 parts each of tin and lead— the latter composition being a little harder. If a little judg- ment is exercised in pouring either of the above alloys, a perfect die will be secured from moist plaster impressions without any drying. As the bismuth is expansive and the alloy is hard and somewhat brittle, I run only a thin casting, not more than half an inch in thickness, over the highest portion of the impres- sion. I have cast-iron or brass heads made, 3J inches in length, 3 inches in diameter at large end, and 2 inches at the other; the large end is flat, and well coated with common tin- man's* solder. This head is heated until the solder begins to soften; it is then placed in a pan or other convenient vessel, and the die, face side up, is placed upon the tinned surface. When the die begins to melt, and perfect union is secured, cold water is dashed upon the die and head ; and thus we have a sharp die, with an iron head, to sustain the force of the blow in stamping the plate, and by this means preventing any spreading of the face of the die or liability of breaking in the process of swaging. " I now take sheet lead of the thickness of about Xo. 24, standard gauge, and adapt it to the face of the die by means of a wooden mallet or burnisher, or other convenient means. Trim the lead plate to the size required for the plate to be stamped; when the lead plate is nicely fitted, remove it care- fully from the die and place it in a ring or narrow molding flask, the palatal side up; now gently stamp molding sand into the plate and flask up level with the edges of the flask; then reverse the flask and cut the sand away clean for half an inch or more down to the edge of the lead plate all around. Around the plate place a common molding ring sufficiently large to form the counter, which is made by pouring melted tin or lead (or any alloys of these metals) on to the lead plate, being careful 194 MECHANICAL DENTISTRY. not to run the metal so hot as to melt the lead plate. When the counter is cool enough to handle, the adhering sand is brushed or washed away; the die is then placed into the bed or counter, and, with a moderate-sized hammer, give one or two sharp blows to bring the die and counter together. In swaging gold plates, two or three, or more dies may be required ; these may be made either by running the die metal into the im- pression (if not broken) or by running into lead plates, gotten up as before described, reserving, of course, the first die and counter for the final swaging of the plate. I have gotten up a die and counter from the impression, with the aid of an assist- ant, in the foregoing manner, in twrelve minutes. I usually get out my die immediately after taking the impression; adapt a wax or gutta-percha plate to the die, and get the articulation before the patient leaves the office." In the act of contracting, the central portion of the die, being the last to solidify, is gradually drawn toward the periphery, forming, when the contraction is completed, an excavation of greater or less depth in the centre of its base, a form unfavorable to an equal distribution of the force applied in swaging, and greatly increasing the danger of distorting the face of the die by cracking or spreading, especially when zinc is used. To concentrate and equalize this force is a matter of the first im- portance. The liability to such an accident may, to some extent, be avoided by placing on the die a cone-shaped cap of any hard metal, as zinc, brass, or cast-iron. This, however, while it provides against one-sided blows of the hammer, affords only a partial remedy, since the same danger of spreading the die exists, in consequence of the cap resting on the outer border of the base of the die, with no central bearing whatever. To equalize the force perfectly, the cone-shaped metal cap should be incorporated with, and form part of, the body of the die itself. This is partly, if not wholly, accomplished by Dr. Franklin's expedient, but a simpler method, we think, and one that certainly and completely fulfills the requirements men- tioned, is the following, described by Mr. George Ward, of England:— " Having cut the plaster model to its smallest required pro- METALLIC DIES AND COUNTER-DIES. 195 portions—the depth never to exceed two inches, if that—and having*stearined it and prepared the molding sand, which should always be sifted before using or dampening, place the model in the centre of a casting ring, ram well home the sand on the side and top, and withdraw in the usual way. If the sand mold is true, proceed to pour in the melted zinc. Now, as soon as the fluid zinc reaches the level of the sand, place on it a hollow cone of gun metal with a top no larger than the face of the swaging hammer, and with base in proportion. The best practical size of the hollow cone is as follows: Diameter of base, 3f, and cross, 2f inches; top, 2 across, 1\ inches; depth of cone, If inches. The writer has had these cones cast from his own patterns ; they are not round, but the shape of the plaster model. " As soon as the melted zinc reaches the level of the sand mold, place on it one of these cones; see that it is fairly in the centre, and then through the top pour in the rest of the zinc until the cone is full. Before doing this, however, care should be taken to back up the edges of the base of cone with moist sand, and to hold it firmly down in its place, or the fluid metal will raise the cone and the metal overflow. The entire operation takes not nearly so long to do as to describe in writing. After letting the Avhole cool, dig it out, and the gun-metal cone will readily come away of itself, leaving as fine and strong a zinc die as it is possible to procure, which no amount of hammering will ever split or crack. It need not be explained to a truly scientific dental mechanician that the denser and heavier the zinc dies are, the more effectually the blows of the hammer will tell on the plate to be struck up. Not only this, but the now solid, cone-shaped head of the die will enable the blowrs to fall every time on the self-same spot— a fact alone of great importance in striking up plates, and one which should never be lost sight of or neglected." Dipping.—By this process the counter-die is first obtained, and from this the die. For the purpose, two or three sheet-iron pans, varying in size, should be provided, measuring from three to five inches in diameter, and from two to three inches in depth, the open ends of which should be somewhat larger than 196 MECHANICAL DENTISTRY. the bottoms. The metal for the counter is melted and poured into the pan, and immediately before " setting," the' model, being unvarnished and previously well dried, is immersed, face downward, until all parts of the palatal arch and ridge are imbedded in the metal. The chamber, as well as the groove around the outside of the ridge concerned in the forma- tion of a rim to the plate, should, in this case, be formed in plaster. Ordinarily, the conformation of the ridge above and below is such as to render it impracticable to remove the model from the metallic matrix without injury; hence two or more models will be required whenever this method is practiced. After the counter-die and model are separated, all traces of plaster should be carefully washed from the matrix, and the latter surrounded with a sheet-iron ring forced slightly into the counter immediately outside of the cavity formed by the model; into this the metal for the die is poured, filling the matrix and ring. If the metal or alloy forming the die fuses at the same or a higher heat than that composing the counter, the matrix should be protected from adhering to the die by coating its surface uniformly either with lamp-smoke or a thin mixture of whiting and water, or alcohol. Counter-die.—A counter to the die is generally obtained directly from the latter, and may be procured in either of two ways. 1. The die is placed, face upward, upon the molding board, and sand, prepared as in molding, built up around it, leaving only the ridge and palatal face exposed. It is then encircled with a cast- or sheet-iron ring two or three inches deep, its edge imbedded in the sand to prevent the escape of the fluid metal; into this the metal for the counter is poured until nearly or quite full. 2. The metal for the counter may first be poured into a sheet-iron vessel of proper size, and, im- mediately before setting, the face of the die is immersed in the liquid mass and held perfectly stationary until solidification of the counter takes place. The method of procuring a counter- die directly from the plaster model, as in the process of dipping, has already been described. METALLIC DIES AND COUNTER-DIES. 197 The metal commonly employed for the counter is lead, although other substances, as tin, type-metal, some of the more fusible alloys hereafter to be mentioned, etc., are sometimes employed. When the counter is taken by pouring the metal or metals composing it upon a die fusing at a low heat, some caution should be observed lest the two pieces adhere by partial fusion of the die. In such cases the surface of the die should be well protected with lamp-smoke or whiting; the lead should be poured at the lowest practicable temperature, and the con- duction of heat facilitated by surrounding the die with a heavy cast-iron box or ring. To avoid incurring any risk, however, the counter-die, if composed of a less fusible metal or compound than the die, may be first obtained directly from the model, and the die obtained from this, as in the process of dipping; or, a counter of lead, previously taken from a zinc or other more fusible die, may be used. During the process of forcing a plate into adaptation to the form of the mouth with swages, it not unfrequently happens that the marginal portions of the former become wedged or immovably fixed between the outer border of the die and cor- responding portions of the counter before its central portion is forced into contact with the palatal surface of the former, thus rendering it difficult to conform the plate accurately to the parts without the application of sufficient force to deface or otherwise mar the form of the die. In such cases the central portion of the plate may be first swaged with a partial counter, which is made to receive only the palatal portion and upper surface of the ridge of the die. After forcing the central part of the plate into adaptation with the partial counter, the process may afterward be completed with a full counter after having turned the edges of the plate down upon the outer border of the ridge with a mallet and pliers. As before remarked, preference is usually given to lead in the formation of a counter-die, mainly on account of its greater softness. This property in a counter is practically important. In the process of forcing a metallic plate into adaptation to the mouth, partial displacement or yielding of either the die or counter, or of both, necessarily occurs, and it is scarcely necessary 198 MECHANICAL DENTISTRY. to remark that whatever change of form is produced should take place wholly in the counter, otherwise deformity of the die must ensue. Essential Properties of a Die.—There are certain properties which it is indispensable that a metallic die should possess more or less perfectly in order to answer fully the requirements of the dentist. 1. A die should be sufficiently hard to resist any necessary force applied to it in stamping the plate without suffering any material change in the form of its face, by which latter term is meant that portion of the die with which the plate is brought into contact. This property is most indispensable in those cases where the arch of the mouth is very deep, the ruga prominent and sharply defined, and where the alveolar ridge is marked by angular and abrupt prominences and depressions. In such cases, if the die is not sufficiently resistant, the points most prominent upon its face will be bruised or battered down, while the plate will fail to be forced perfectly into the cavities or depressions, and its coaptation to the mouth, to that extent, rendered faulty. The cases in which a less degree of hardness is admissible is where the arch of the mouth is broad and shallow, the ruga imperfectly defined, and the ridge regular and symmetrical. The conformation of the mouth, therefore, will, in respect to the property of hardness, admit of some latitude in the choice of the metal or alloy employed in the formation of a die. 2. Another important property of a metallic die is non- contraction, so far, at least, as this is attainable. Inasmuch as the successful adaptation of the plate depends, in a great meas- ure, upon an accurate representation of the precise form of the mouth in the die, it is of the first importance that the latter, other essential requisites being secured, should be composed of some metal or metals having the least possible contraction in cooling. Contraction is, in varying degrees, common to all metals exposed to a decreasing temperature, and it is impos- sible, therefore, to obtain a perfectly faultless copy of the mouth in metal. Fortunately, as well for the expert as the unskilled manipulator, the unavoidable shrinkage incurred is partially METALLIC DIES AND COUNTER-DIES. 100 or wholly compensated for by the expansion of the plaster and the yielding condition of the soft tissues of the mouth, but under no circumstances should the accommodation afforded by the condition last mentioned encourage negligence or unskill- fulness in the use of .all available means necessary to secure the most accurate adaptation of the base. Ordinarily, a moderate degree of contraction will not materially impair the fit of a plate; on the contrary, in the case of the upper jaw, it some- times favors its adhesion and retention in the mouth. Cases, on the other hand, frequently occur where the least practicable amount of shrinkage, even at the partial sacrifice of other properties, becomes indispensable in the die. 3. A third important requisite of a die is fusibility. Aside from the convenience incident to the use of metals which fuse at a low heat, there is another consideration favoring this prop- erty of more practical importance. It is well known that all metals expand by heat and contract by cold. In obedience to this law, metals fusing at a high heat suffer a greater aggregate contraction than those melting at a lower temperature, and, as between two metallic bodies of equal dimensions, liquefying at different temperatures, the difference in contraction will corre- spond exactly with the difference in the number of degrees through which each passes from the point of solidification to the mean temperature of the air, allowance being made for the difference in their ratios of contraction. Two dies, one com- posed of copper and the other of zinc, will serve to illustrate. Fused copper solidifies at 1900°. In cooling, therefore, it con- tracts through over 1800° to reach a working temperature, while zinc, fusing at 773°, contracts through only about 700° to reach the same temperature. As before stated, the difference in the contraction of metals will be somewhat modified by that in their ratio of contraction, but it will always be found that the more fusible metals have the least aggregate shrinkage whenever any considerable disparity exists between their fusing points. It is in accordance with the principles here set forth that the more fusible alloys, some of wThich melt at remarkably low tem- peratures, are employed whenever it is important to obtain a die as nearly the exact counterpart of the model as possible. 200 MECHANICAL DENTISTRY. 4. Finally, a die should be sufficiently cohesive to resist the repeated blows of a heavy hammer without parting or crack- ing. Many metals, as antimony, bismuth, etc., in other re- spects suitable for dies, are objectionable on account of brittle- ness. But it must not, therefore, be inferred that all metals that are denominated brittle are inadmissible for this purpose; for zinc, which, in its ordinary condition, is ranked as a brittle metal, and type-metal, which is always so, are in no clanger of being forced asunder or of suffering displacement when in the compact form of a die, provided the force used in swaging is judiciously applied, or proper form and sufficient depth are given to the body of the die. To recapitulate briefly: a die should be formed of some metal or alloy that has a surface hardness sufficient to resist compression; that fuses at a low temperature; that does not, in any material degree, contract in the act of cooling; and whose particles adhere with sufficient cohesive force to main- tain perfectly its integrity of form under the hammer. Any one or two of these properties are readily attainable in the same die, but no one known metal or alloy combines all of them per- fectly. Thus either cast-iron, brass, bronze, or cannon metal would form an excellent material in respect of surface hardness, and in the compact form of a die would be sufficiently cohe- sive, but few enjoy convenient facilities for melting them; besides, their great contraction consequent upon their high fusing point would render their employment entirely inad- missible. Again, certain alloys, as those composed of lead, tin, and antimony or bismuth, are eminently suitable on account of their extreme fusibility and comparative exemption from shrinkage, but they gain these properties at the expense of that degree of hardness necessary to resist compression. Tin in its uncombined state is ordinarily sufficiently fusible, tenacious, and non-contractile, but is too soft and yielding when forcibly compressed. Antimony and bismuth are sufficiently hard, fusible and non-contractile, but are objectionable on the score of extreme brittleness. Any metallic substance that combines most perfectly the several properties referred to is, therefore, best adapted to the METALLIC DIES AND COUNTER-DIES. 201 necessities of the mechanical operator, and experience has almost universally accorded pre-eminence in this respect to zinc. It presents a more resistant surface to the blow of a hammer than either copper or brass, three times more so than that of tin, and more than double that of type metal. As it usually occurs in commerce it may be classed as a brittle metal, but when annealed it is tough and malleable. It melts at a heat (773°) which may be readily commanded, and contracts but little in cooling. The late Professor Austen demonstrated by actual experiments that an average-sized zinc die measur- ing two inches transversely, contracts yf^- of an inch from outside to outside of the alveolar ridge, being equivalent in thickness to three ordinary leaves of a journal. Professor Austen remarks: " in the first case (upper jaw) the plate would ' bind,' and if the ridge were covered by an unyielding mucous membrane it wrould prevent accuracy of adaptation. In the second case (under jaw) the plate would have too much lateral ' play,' and consequently lack stability. Again, in a moderately dee}) arch, say half an inch in depth, the shrinkage between the level of the ridge and the floor of the palate will be nearly TffVo — rather more than one leaf of a journal. In the deepest arches this shrinkage becomes a serious difficulty; in the shallower cases it is not of much moment, as there is no mouth so hard as not to yield the toW °r hot of an inch. As before stated, a moderate degree of shrinkage in the die may, in certain conditions of the mouth, practically favor the adhesion and permanent retention of a plate applied to the upper jaw. The conditions alluded to, and which prevail in a greater or less degree in all cases, are, soft and yielding ridge and comparatively hard and unimpressible palate. Now, if in the first instance the plate is swaged into uniform contact with all parts of the jaw, it will be readily perceived that if pressure is made over the ridge on one side the latter will yield, while the central portion of the plate, meeting with a fixed point of resistance at the floor of the palate, will " ride " upon the latter, and thus throw the plate from the ridge on the opposite side of the jaw. If, however, a space equal to one or two thick- nesses of the plate exists between the latter and the roof of the 202 MECHANICAL DENTISTRY. mouth,'as a consequence of contraction in the die, the plate, as it is carried against the palate, in the act of exhausting the air from beneath it, will at the same time forcibly compress the ridge, securing thereby a more resistant basis along the border, and providing more certainly against displacement of the base on the application of forces brought to bear upon it in mastication. The extent to which the shrinkage of a die may be admitted in any given case, will depend partly upon difference in the conditions, heretofore mentioned, in the soft parts of the mouth, and in part, also, upon the general configuration of the jaw. In a medium-sized mouth, with a depth of say half an inch to the arch, a moderately soft ridge and resisting palate, the shrinkage incident to zinc will be unimportant, and in many cases will be advantageous. If, however, the vault is very deep, even though there be a yielding ridge, the unavoidable con- traction of a zinc die will throw the plate so far from the arch as to render it difficult for the patient to exhaust the atmos- phere from between it and the floor of the palate, and even when the latter is practicable, the plate will bind with such force upon the outer border of the ridge as not only to produce pain and irritation of the compressed parts, but the resistance afforded at these points will be sufficient, in many cases, to break up the adhesion and force the plate from the palate. Again, as an extreme case, if the ridge and palate are some- what uniformly unyielding, and the palatal vault is, at the same time, very deep, a zinc die can only be made available in bringing the base as nearly into adaptation as possible, after which the operation may be completed with a swage having a less degree of shrinkage, and which, as a mere finishing die, need not necessarily be so hard as zinc. In conforming a plate to the lower jaw, the die should be as free as possible from contraction in all cases. The greatest shrinkage in such cases will be between the posterior extremi- ties of the ridge, giving too much lateral play to the plate; in addition to which the posterior and inner edge of the base, projecting out from the ridge, will obstruct the free action of the tongue, while the latter will tend to lift it from the ridge and render it unstable. These conditions may be partially METALLIC DIES AND COUNTER-DIES. 203 remedied by turning the edge of the plate in against the ridge with pliers; but this expedient should never be resorted to in any case whenever it is practicable to secure a correct adapta- tion by swaging. In all cases in which a zinc die fails to bring the plate into proper adaptation to the parts, either of the following metallic compounds may be used to complete the process after partial stamping with zinc. Type Metal,—Lead, five parts; antimony, one part. Fuses at 500°; contraction less than one-half that of zinc; more compressible than the latter and very brittle. Babbitt, or Antifriction Metal.—Copper, three parts; antimony, one part; tin three parts. First fuse the copper, and then add the antimony and tin. Melts at a moderately low heat; con- tracts but little; is brittle, but may be rendered less so by adding tin. Zinc, four parts; tin, one part. Fuses at a lower heat, con- tracts less in cooling, and has a less surface hardness than zinc. Tin, five parts; antimony, one part. Melts at a lower heat than either of the preceding alloys; contracts but slightly in cooling; is harder than tin, and sufficiently cohesive. It is readily oxidized, and should be poured as soon as melted. Fusible Alloys.—The following tabular view of the more fusible alloys, the respective properties of which are deduced from actual experiments, was given by Professor Austen, in a paper on " Metallic Dies."* Zinc is introduced into the table for the purpose of comparison. Melting Contrac- Hard- Brittle- point. tility. ness. ness 1. Zinc............... 770° 440° 340° .01366 .00633 .00500 .018 .050 .040 5 3 3 2. Lead, 2, Tin, 1........... 3. Lead, 1, Tin, 2........... 4. Lead, 2, Tin, 3, Antimony, 1..... 420° .00433 .026 7 5. Lead, 5, Tin, 6, Antimony, 1..... 320° .00566 .035 6 6. Lead, 5, Tin, 6, Antimony, 1, Bismuth, 3 300° .00266 .030 9 7. Lead, 1, Tin, 1, Bismuth, 1...... 250° .00066 .042 7 8. Lead, 5, Tin, 3, Bismuth, 8..... 200° .00200 .045 8 9. Lead, 2, Tin, 1, Bismuth, 3..... 200° .00133 .048 7 * American Journal of Dental Science, vol. vi, page 367. 204 MECHANICAL DENTISTRY. Professor A., in commenting on the preceding table, ob- serves : " The last column contains an approximate estimate of the relative brittleness of the samples given. As in the other columns, the low numbers represent the metals, so far as this property is concerned, most desirable. Those marked below 5 are malleable metals; those above 5 are brittle; zinc, marked 5, separates these two classes, and belongs to one or the other, according to the way in which it is managed." Allusion is here made to the process of annealing zinc, and which has already been adverted to when considering the latter metal in the former part of the work. The special method employed is thus described by the author already quoted. " The simplest way to anneal a zinc die is to place it in the melting ladle with about a tablespoonful of water, removing it in thirty seconds after the water has boiled away. If the fire is a very hot one, remove it immediately on the disappearance of the water. It will often happen that the die is annealed in the process of taking the counter-die. This will more certainly occur when Nos. 7, 8, or 9 (see table) are used for the counter. For example, take tin, using a mass twice the size of the die, should it be heated to 540° (100° above melting point), it would not, allowing for loss of heat by radiation and contact with the cast-iron ring (if one be used), heat the zinc beyond 330°. Lead, cast as cool as it could possibly be poured, unless in a very heavy ring (such as a ' cart-wheel box '), or in quantity too small for a well-shaped counter, would be apt to raise the zinc at least to 400°, and so impair its malleability, whilst, if poured as hot as many are in the habit of doing, the zinc will remain as brittle as when first cast."* * To the late Professor P. H. Austen, whose various contributions relating to the mechanical department of practical dentistry have done much to unfold and elucidate the principles involved in the practice of this important specialty, the author would acknowledge his indebtedness for many of the valuable data and practical suggestions that may be found embodied in the foregoing chapter ; and, had not the limited space assigned us compelled a condensation of his views on the subject of metallic dies and counters, we might have done the reader an essential service by transferring to our pages many of his eminently practical observations on the subject entire. CHAPTER V. PARTIAL DENTURES. The almost unlimited modifications in the form of substitutes designed to supply the loss of a portion only of the natural teeth, and the difficulties oftentimes incident to a harmonious arrangement of the teeth of replacement, as well, also, as the impracticability of always securing a perfectly satisfactory and efficient antagonism or closure of the artificial with the natural organs, frequently surround this process with peculiar embarrasments, and often render their successful application extremely difficult. They will, accordingly, be found to de- mand of the operator the exercise of greater skill, ingenuity, and discrimination than are usually required of him in the con- struction and application of entire dentures. Certain general and characteristic forms of substitutes of the kind under consideration derive their distinctive character from the several means employed in fixing or retaining them in the mouth. These means of retention may be classified as follows:— 1. The roots of the natural teeth as supports for single artificial crowns, and for so-called bridge-work. 2. Clasps attached to the remaining natural teeth. 3. Bearings of wood attached to tubed plates. 4. Atmospheric pressure and adhesion. Under the first head, the various methods of attaching single artificial crowns will be first considered, and in close connection therewith the somewmat allied method of replace- ment known as bridge work. ROOT CROWNING. The process of attaching an artificial crown to the root of a natural tooth has long been practiced, and when skillfully per- formed under conditions and circumstances that justify the operation, it affords one of the most valuable of all the means of substitution. Formerly, the operation was almost wholly 205 206 MECHANICAL DENTISTRY. confined to single-rooted teeth, and chiefly to the six upper front teeth, but more recently its application has been so extended as to embrace all classes of teeth that can be reached with a facility adequate to the successful manipulation of the necessary instruments and appliances. The uses of this special process have also been greatly aug- mented by the increasing success attained in the conservative treatment of crownless roots. To the multiplicity of ingenious and practicable devices in the construction and modes of attachment of artificial crowns, and a corresponding develop- ment of a higher order of manipulative skill, are added more rational, comprehensive and effective therapeutic agencies, thus, in a manner, supplementing modern improvements in mechanical devices, and extending and multiplying more and more the conspicuous benefits which lie fairly within the range of possibilities in the practical application of this invaluable method of replacement. There are, however, limits to the utilization of these means of support. There are many roots wholly unsuitable for the purpose. The operation may be said to be valuable in pro- portion as the artificially-crowned root can be made inoffensive, comfortable, serviceable, and durable. A pulpless root that is extensively softened, or that is greatly denuded from excessive absorption of the surrounding alveolus, or very loose in conse- quence of extended destruction of the investing membranes, cannot, in any degree, meet these requirements. Between these extreme conditions on the one hand, and those associated with partially crownless roots with the pulp intact, the investing membranes free from disease, the cervical portions of the bony structure unimpaired by decay, and a firm attachment to the socket, conditions representing, on the other hand, an opposite extreme, there are gradations of normal and abnormal states which, while they may not exclude the operation, must, in some degree, impair its value. Any estimate of the absolute value of this method of substitution that excludes a recognition of this fundamental truth is a false and unwarranted one, and there can be no rational prognostication in these cases that does not admit this truth as an essential element in forecasting results. ROOT CROWNING. 207 Not only will results be modified by conditions immediatelv associated with the root to be operated on, but also, to some extent, by the general health of the mouth. Any abnormal states of either the hard or soft tissues, or the presence of foreign deposits, will act as predisposing causes in the development of unfavorable conditions whenever the root operated on has, previous to curative treatment, been morbidly affected, and especialty if such diseased conditions have been somewhat virulent and of long standing. It is best, therefore, in all cases to inspect the mouth carefully, either before or immediately after attaching the crown, and if any of the remaining teeth are found carious, or incrusted with tartar, or the mucous membrane and gums are inflamed or otherwise diseased, appropriate treatment should be directed to the correction of such abnormal conditions as may be present. In the less favorable class of cases, or where the root has been previously diseased, though subsequently restored to a healthy condition, any diathesis, or constitutional tendency, predisposing to inflammation or suppuration, may become a factor in the development of unfavorable results. Whenever this predisposition exists in any marked degree, the operation should be performed in the most careful manner, avoiding as far as possible all sources of irritation in the use of files, saws, drills, and in tamping or malleting, and especially in the use of excising forceps for the removal of any remaining portions of the crown. Should tenderness or loosening of the root supervene after the necessary preparation of the root, and before setting the crown, it will be prudent to defer the com- pletion of the operation until there is subsidence of the morbid conditions, for, if, by reason of such irritation or inflammation, suppuration should be re-established, it may be necessary to free the pulp canal and renew treatment through the apical foramen. The success of the operation may also be greatly impaired by careless, hurried, and injudicious manipulation; as where the remaining portions of the natural crowns of the tooth are violentlv removed with excising forceps, or by the unskillful use of files in dressing the root, or drills in enlarging the 208 MECHANICAL DENTISTRY. central cavity, or by undue or misapplied force in the final adjustment of the artificial crown, or, finally, by a faulty position of the tooth of replacement, by which the root is sub- jected to injurious strain, either by lateral pressure or premature closure against those of the opposite jaw. By the operation of either or all of these causes, disease of a more or less intractable character may be induced which will impair the usefulness of the artificial organ and subject the patient to much present and future distress and annoyance. Preparation of the Root.—In the process of preparing the root for the attachment of an artificial tooth, all remaining portions of the natural crown should first be removed with suitable instruments. If the cervical portion of the tooth is com- paratively sound and unbroken, this may be most expeditiously accomplished, and with less risk of injury to the root, by employing a very fine saw attached to a steel frame or carrier, as shown in Fig. 79. The saw should be narrow enough to Fig 79. enable it to take a curvilinear direction in cutting, as this will enable the operator to separate the crown nearly or quite on a line with the arched margin of the gum, thus dispensing, in a great measure, with the use of other instruments in the final dressing of the cut end of the root. The saw should be passed along the side of the tooth to the gum, and the crown separated either by cutting directly across to the opposite side, or as nearly on a line with the curvature of the anterior and posterior margins of the gum as possible without wounding the latter. During the operation the saw should be kept constantly wet, and the crown should be sup- ported by the fingers. If the remains of the crown are friable, or if they consist of but fragmentary portions of enamel, they may be readily cut away with excising forceps, two forms of which are exhibited in Fig. 80. The one having square, transverse cutting edges closing at right angles with the shaft is generally employed. ROOT CROWNING. 209 Serious, if not irreparable, injury may be inflicted by the care- less or unskillful use of this instrument, either by producing so violent a concussion as to induce, in some instances, incurable disease or absolute necrosis of the root, or by frac- turing the latter in such a way as to unfit it for the reception of the artificial crown. The forceps, therefore, should never be used to excise the crown with a single cut whenever any con- siderable portion of the root at the gum remains unaffected by disease, and even when the latter is friable or partially destroyed by decay, they should be used with great caution, cutting or chipping away small portions at a time until as much of its substance is removed as is practicable with the forceps. After the use of the saw or excising forceps, any remaining portions projecting beyond the free margins of the gum should Fig. 80. then be removed and proper shape given to the end of the root. A half-oval file, with a sharp and tolerably fine cut running obliquely across its convex surface, or suitably formed corundum burs or disks, are the best for the purpose, and when in use, should be kept constantly wet and free from clogging particles of bone. The end of the root should be dressed down, anteriorly, at least, a little below the free margin of the gum, care being taken not to lacerate its peridental attachment; in this way the artificial crown, when adjusted to the root, will unite so intimately with the gum in front as to render exposure impossible. The surface of the root prepared in this manner will present a concavity corresponding with the festoon of the gum. 14 210 MECHANICAL DENTISTRY. If a living pulp remains in the root, it will not ordinarily be practicable, unless there is partial obliteration and conse- quent recession of the pulp cavity as the result of ossific de- posits, either to saw off the root on a line with the gum, or even transversely, or to dress the root even with the gum, with- out inflicting insufferable pain. It will be necessary, therefore, either to extirpate the pulp through the carious opening in the crown before the latter is removed, or, if not exposed by the operation of sawing or filing, through an opening into the pulp made with a drill or cutting instrument after excision. There are several ways of extirpating a living pulp. One of the older, and still not uncommon, methods of operating con- sists in first devitalizing it with arsenious acid, and afterward remove with a broach. This violently irritant substance can- not be used for such a purpose without great danger of seriously endangering the vital connection existing between the root and its pericemental covering, as well as of fatally implicating other associated tissues, and should therefore never be employed. It is of the first importance, in setting artificial crowns, that the organ relied upon for support should be secured against any impairment of its normal circulation and nutrition, and the removal of the pulp should, therefore, be effected in such manner as not to implicate the investing membranes. This may generally be accomplished by direct operation with appro- priate instruments, usually with a three- or four-sided, barbed, untempered broach, which, being small enough to penetrate freely to the apex of the root, is thrust quickly to the terminal point of the canal, rotated, and withdrawn ; when, if the entire pulp does not come away with the broach, the operation may be repeated, with comparatively little pain, until all portions of it are removed. The pain of such an operation may be mitigated or wholly obviated by the use of local anaesthetics, as ether spray, cocaine, etc. A somewhat heroic method is now occasionally resorted to, by which a living pulp is quickly and successfully devitalized and removed, with, it is claimed, comparatively little pain. This consists in shaping a piece of hickory or orange-wTood as nearly as practicable in conformity to the length, size, and general ROOT CROWNING. 211 form of the pulp canal to be operated on, dipping it in carbolic acid, and driving it with a single stroke of a light mallet to the apex of the root. On removal, the entire body of the pulp will not unfrequently come away adherent to the stick; if not, any remaining portions may be removed, without pain, with a barbed broach. This method is now more or less practiced by those making the setting of single crowns and bridge-work a specialty. Though but recently adopted to any considerable extent, its origin dates back many years, its first employment being ascribed to Dr. George Lawrence more than thirty years ago. The instantaneous and more or less complete subversion of sensation in the pulp induced by this operation has its analogy in the application of the actual cautery, the immediate paralysis induced rendering both operations comparatively painless. Fig. 81. J 1 1 " 1 After the removal of the pulp, the apical foramen should be thoroughly closed by any method usually employed in root filling. A. neglect of this important measure will greatly endanger the success of the operation. The proper treatment and preparation of the root having been thus far accomplished, the canal of the latter should next be enlarged for the reception of a dowel-pin. This is effected with a suitable broach or with drills of various forms. When the canal presents the form of a cleft or fissure, a spherical or cone- shaped bur drill should be used; if, however, the pulp canal approaches a cylindrical form, the operation will be more speedily performed with a four-sided broach, or, what is still better, a spear-pointed or spiral drill, all of which are exhibited in Fig. 81. The natural opening in the root should be enlarged 212 MECHANICAL DENTISTRY. to the depth of from one and a half to two or more lines, according to the length of the root; and the orifice should be made large enough to admit a support of sufficient size to secure the crown firmly in position. The direction of the drill in cutting should follow closely that of the natural canal in the root, since but a slight deviation in this respect may en- danger the integrity of the latter by too great a thinning, or actual perforation, of its wTalls. In many cases, however, where the direction of the canal will admit of it, the shaft of the instrument should be held steadily on a line with the circle formed by the cutting edges of the adjoining teeth, and either equidistant between the latter or with such a lateral inclination as will give to the tooth of replacement a symmetrical arrange- ment in the arch. During the operation, the drill should be kept constantly wet, and loose particles of bone should be washed from the cavity by occasional injections of water. Fitting the Crown.—The crown selected for any given case should correspond, as nearly as possible, in size and general configuration, with its fellow of the opposite side, or, where several are inserted, with the form and size of the natural organs which they represent. The tooth or teeth of replace- ment should also harmonize in color with those immediately adjoining. The cervical portion of the crown applied to the root should correspond, as nearly as possible, in dimensions, with the filed surface of the root, and the adaptation of the two surfaces should be sufficiently accurate at all points to afford a firm basis for the crown, and, at the same time, to exclude perfectly all particles of alimentary or other solid substances, the decomposition of which would tend to the decay or disease of the root, or become offensive in the mouth. To secure such a coaptation of the articulating surfaces, more or less dressing of the root and grinding from the base of the crown will be required, so that, while uniform contact of the surfaces is secured, the artificial crown will be made to occupy its proper relative position in the arch. The articulation of the crown and root may be very accu- rately obtained in the following manner: Attach to the crown temporarily a piece of wood that may be easily applied and ROOT CROWNING. 213 removed; coat the surface of the root uniformly with some pigment, as carmine, rouge, or rose pink, and apply the crown, with wood pin attached, to the root; the points of contact will be indicated upon the base of the crown by the adherent coloring matter; the colored portions are then ground dowm somewhat, on an emery wheel, and this process is repeated until the entire surface of the base of the crown exposed to the pigment becomes uniformly coated. Whenever it is thought important to preserve the form of the porcelain crown unchanged, the operation may be reversed by coloring the base of the latter and filing from the extremity of the root until a perfect adjust- ment of the parts is secured. Another method, sometimes employed, may be adopted, and will secure an equally accurate bearing of the crown without subjecting the patient to the annoyance of repeated trials of the latter in the mouth. After having prepared the root in the manner already described, an impression of the root and contiguous teeth is taken, and from this a plaster model is obtained. The drilled cavity in the root will be indicated on the model by a corresponding depression; this may be extended into the body of the latter with an instrument fitting the orifice and held in the exact position as when enlarging the canal in the root. The model is then varnished, and a pin being temporarily attached to the crown, the base of the latter may be ground, with or without the use of coloring matter applied to the model, until the articulating surfaces close uniformly, and the crown occupies the required position indicated by the adjoining teeth represented on the model. If the impression is correct, and the manipulations are accurately conducted, a crown prepared in this manner will be found to fit the root and occupy a proper position in the circle with but little, if any, additional filing or grinding. Attaching the Crown by Means of Wood Dowel-Pins.—The older and less expensive method of fixing artificial crowns to the root of teeth is by means of wood dowel-pins. Thoroughly seasoned white hickory, of small growth, fine-grained, and straight, com- pact fibres, is esteemed the best for the purpose. This substance is often used in its natural condition, but it will be much 214 MECHANICAL DENTISTRY. improved, both in respect of strength and durability, if pre- viously well condensed by forcing it through the holes of an ordinary draw-plate, or, what is better, through apertures of various sizes formed with smooth beveled edges in a piece of ivory, steel, or porcelain of sufficient thickness. Cylinders of wood, of uniform thickness throughout, are most conveniently formed by splitting the timber into rods five or six inches in length, and from one-eighth to a quarter of an inch in diam- eter, trimming them, with suitable instruments, to a size one- third larger than required when condensed, and then passing them through the holes of a draw-plate, on the side where they form a cutting edge, commencing with the larger and passing to those of diminished calibre, until a cylinder of the size mentioned is obtained. These are then compressed in the manner before mentioned. When the draw-plate is used to compress the wood, the latter should be passed through from the opposite side of the plate. Fig. 82. One end of the dowel-pin, dressed to the proper size, is made to fit accurately the hole in the crown, care being taken not to fracture the latter when forcing the former into place. The depth of the enlarged opening in the root will determine the length to be given to the end of the pin projecting from the crown, and the former may be readily determined by means of a gauge (Fig. 82), consisting of a rod of wire of a size to enter freely the canal in the root, with a movable slide, to the end of which is attached a circular collar or flange. The end of the wire being pressed to the bottom of the canal, the flange, rest- ing against the end of the root, will force the slide back upon the rod, and thus indicate with certainty the depth of the canal. The pin being cut off at a point distant from the crown equal to the length of the uncovered end of the wire, is then dressed to the size of the orifice in the root. The pin should be accurately fitted to the canal in the root, but not so tightly as to ROOT CROWNING. 215 require any greater force in adjusting the crown to the root than may be readily applied with the fingers. A wood pin thus easily applied will, wThen enlarged by the absorption of fluids, be so firmly retained as to render its removal difficult; and even when moisture is excluded, adequate stability will be imparted to the attachment, provided sufficient depth is given to the cavity in the root. It may be observed, however, that any method of crowning that does not effectually exclude the secretions of the mouth is objectionable. The too frequent method of fixing artificial crowms with cylinders of wood, without providing for the exclu- sion of the oral secretions and pulpy portions of food, not only hastens the destruction of the root, but, in addition to being positively harmful, cannot fail to bring a desirable method of replacement into general and merited disrepute by reason of the offensive odors accompanying the animal decomposition inseparably associated with such a mode of procedure. To provide against the intrusion of secretions or portions of alimentary substances, either of the following expedients may be adopted :— If the coaptation of the prepared surfaces of crown and root in contact is accurate and uniform, one or two thicknesses of No. 5 or 6 gold foil, or corresponding thickness of tin foil, interposed when the crowm is forced to its place, will exclude the secretions with tolerable certainty. Such plastic substances, however, as are impervious and insoluble will more certainly accomplish the object in view, and among these Hill's stopping is generally esteemed the best. Amalgam may also be used for the same purpose, in which case the central portion of the articulating surface of the root should be somewhat countersunk. It not unfrequently happens that a cone'or funnel-shaped enlargement exists at the orifice of the root-canal, as the result of decay. In such cases it will be difficult and often im- practicable to adjust a crown securely without preliminary treatment of the root. Firmness of attachment, in these cases, may be secured in 216 MECHANICAL DENTISTRY. either of the following ways: 1. Having removed all softened or decayed material from around the orifice of the canal, and enlarged the latter to the depth required for a dowel-pin of ordinary length, the canal so prepared, together with the carious excavation, may be filled compactly with gold flush with the margins of the dressed end of the root. Through this a central passage is made with suitable drills for the admission of the pin. 2. A highly polished and uniformly cylindrical steel wire, somewhat smaller than the prepared opening in the root, may be introduced into the latter and gold packed around it and into the excavation, flush, as in the former case, with the margins of the root, after which the steel wire is carefully withdrawn. In either of the above cases the gold should be securely fixed in place, in the first instance by forming small pits or circular grooves in the walls of the enlarged canal, and 'by retaining-points in the sides of the excavation. Dowel-pins of Metal and Wood.—Pins are sometimes formed of gold wire encased in wood. These impart additional strength to the attachment, and, at the same time, enable the operator to change the direction of the crown by bending the pin whenever the root stands irregularly in the arch. A hole, some- what smaller than that in the root, is drilled into a block of hickory wood, and into this is forced a gold wire—that formed of gold and platinum being the best, as it possesses greater stiffness and elasticity. The wood is then dressed down to a size a little larger than the canal in the root, and then compressed. One end being fitted to the hole in the crown, the projecting portion, cut to the proper length, is trimmed to fit the opening in the root, and applied in the manner before described. Another method is to close the hole in the crown with a cylin- der of wood, trim the latter even with the base of the crowm, perforate its centre with a drill, and introduce into this one end of the wire, the surface of which is cut up into small barbs, or otherwise roughened, to prevent it from drawing. A similar piece of wood is fitted to the orifice in the root, and trimmed and drilled in like manner for the reception of the wire— the latter being barbed and filed square, to render it stationary when forced into place. ROOT CROWNING. 217 The author, in a number of cases, has adopted the following methods of inserting pivot teeth, in connection with the use of rubber, with gratifying results. Having prepared the root in the ordinary manner, select and fit the crown to the vacuity, leaving something of a space posteriorly between the base of the crown and the root. Fit a temporary wood pin to the enlarged opening in the root, accurately, but in such a manner that it may be easily withdrawn; the end projecting from the root should be trimmed down say to half the diameter of the hole in the crown, so that when the latter is applied in the manner to be mentioned directly, some latitude of movement will be provided, admitting of a proper adjustment of the crown when applied to the space. With the wood pin in the root, fill the hole in the crown with stiffened wax, warm the crowm sufficiently to soften the wax, and apply it to the root in the desired posi- tion with respect to the other teeth. When the wax has hardened somewhat, withdraw the crown carefully on a line with the pin, bringing the latter with it; then add sufficient softened wax to the base of the crown to fill in the gap or space between the crown and root; replace the tooth with the pin attached, and press up until the crown again takes its proper position in the vacuity. By this means we get an impression of the filed extremity of the root, and at the same time secure an accurate relation of all the parts. The crown and pin are then carefully removed. Now take plaster and pour a small quantity on a piece of paper or card and sink the pin into it until the surface of the wax at the base of the crown rests upon the plaster, and then build the latter up upon the front part of the crown to the cutting edge, thus forming a shallow bed for its anterior face. When the plaster has hardened, warm the model to soften the wax, and then remove the crown and wax ; the pin will be found remaining in the model, but which, if previously oiled, can be readily drawn. We have now in the model an accurate representation of the end of the root, the'size and direction of the root-canal, and, when the crown is replaced in its shallow bed, also the space between the crown and root to be filled in with rubber. 218 MECHANICAL DENTISTRY. The hole in the model, corresponding with that in the root, should be enlarged somewhat, and this may be done with the same drill used in enlarging the orifice of the root. After var- nishing the hole in the model, pack in softened rubber until full, and insert into this the gold wire previously heated, the crown end of the wire projecting a line or so. Next fill the hole in the crown with rubber, heat the crown, and press it down upon the model and over the gold wire until the crown goes accurately into the depression made for it in the model. Then pack softened rubber into the space between the base of the crown and the model until it is filled in compactly. The whole is then encased in plaster, confined in a flask, and vul- canized. If the foregoing manipulations are carefully conducted the crown will go to its place in the mouth with unerring accuracy, and, by placing one or two thicknesses of gold foil between the rubber and the root, or some plastic material, as Hill's stopping, the joint will be rendered impervious. There is still an additional advantage in this method. All are aware of the liability of a wood pin drawing from the crown, where the latter is short and the hole in it shallow. The wired rubber pin, vulcanized in the crown, cannot be drawn from the most shallow cavity without fracturing the crown. In very many cases this circumstance is of great value. In substituting a plate tooth for the perforated crown in connection with the use of rubber the following method may be pursued: Fit a metallic wire, composed of gold and pla- tinum, accurately to the enlarged opening in the root, but not so tightly but that it may be readily withdrawn. Select and fit a suitable plate tooth, and solder to this a moderately thin gold backing. If, on reapplying the crown, with the wire in place, the former is crowded forward out of proper position by the pin, cut a slot in the latter, and, if necessary, groove the gold backing and crown at the base of the latter until the crown will take its required place, and the projecting portion of the wire lies in close contact with the gold backing for a distance sufficient to insure adequate strength of attachment when the two are united by solder. When the crowm is thus adjusted to the wire, secure them in this relation with wax or ROOT CROWNING. 219 plaster and remove them carefully; imbed in plaster and unite them securely with solder, and then proceed to take an accurate impression of the end of the root in connection with the united crown and pin. This may be done by first filling in over the dressed end of the root with a sufficient quantity of soft- ened wax, forcing the crown and pin into place, and then moulding the wax with the finger to the end of the root and over the backing. Trim away superfluous portions of wax, remove carefully, imbed in plaster in the same manner as de- scribed in connection with the perforated crown, form a matrix in plaster, pack with rubber, vulcanize, dress down to the form of adjoining crowns, and polish. To secure more perfectly the attachment of the rubber, the porcelain crown may be sufficiently undercut with a corundum disk along the sides of the gold backing, to bind the rubber, and this should be done either before or immediately after soldering the pin to the crown. When employing either of the foregoing methods, the pin should be well barbed, and the joint between the crown and root sealed, either by interposing folds of soft foil or by some durable and impervious plastic material, when the crown is finally and permanently adjusted. The following methods of setting an artificial crown are applicable to all cases admitting of this mode of substitu- tion, but will be found of especial utility under certain circum- stances or conditions which exclude the use of simple per- forated crowns, or which at least render their employment difficult and unsatisfactory. It frequently occurs that the root to be used occupies a posi- tion in the arch inconsistent with a harmonious arrangement of the tooth of replacement by the usual method of attaching a so-called " pivot" crown. Thus it may lie closely against one or other of the adjoining teeth, distant from the centre of the space; or it may have too great an anterior or posterior obliquity, or too great a lateral inclination; or, again, it may range with the other teeth with respect to its direction, but may occupy a position entirely within the circle; in either case it will be difficult or impracticable to give a proper relative position to 220 MECHANICAL DENTISTRY. the crown in the usual way. It is true that any slight devia- tion from a just position or inclination of the root may be compensated for by a corresponding inflection of the pin, or by forming an abrupt angle to it where the crown and root unite, or by placing the pin on one side of the hole in the crown; but when the irregularities spoken of exist to any considerable extent, it will become necessary to adjust a plate to the root, and attach to the base an ordinary plate tooth, to which any desired position may be assigned. One of the simplest and most practicable methods of per- forming this operation is thus described by Professor Edwin T. Darby:— " After this (the proper preparation of the root) has been thoroughly done, select a piece of gold or platinum wire (a), Fig. 83, of the diameter of the opening in root, and fit nicely to the opening, letting it project one-eighth inch beyond the Fig. 83. J^-° 1. A l®t T end of the root, that it may be readily removed and inserted in the root during the operation. Next select a thin piece of platinum, of which make a cap with a hole to fit around the wire pivot snugly, and over the whole end of the root (6). This is then placed in position on the pivot and the pivot in- serted in the root, and, with hammer and punch, the plate is driven down until it fits every part of the root well; then, with a sharp-pointed instrument, mark around the wire to indicate the position. After this has been done, with the pliers, remove both cap and pivot together, and solder one to the other (c). Again insert the pivot and cap, and repeat the hammering until every point fits the end of the root, and, when in position, take an impression of it and the adjoining teeth, either with plaster or No. 2 impression compound. Next re- move the pivot and put it in the imprint made in the impres- sion, and fill the impression with equal parts of plaster and ROOT CROWNING. 221 pumice stone. The next stage is to grind the porcelain plate tooth to fit the cap and gum on the labial border; then back the tooth with gold, 22 karats fine, and solder with 20 karat solder. If pumice and plaster have been used for the model, it may be soldered without removing from the model, by simply adding enough of the same mixture to hold the tooth in position upon the model, and, by soldering upon the model, lessens the danger of displacing during the process of trans- ferring from model to investment. " We now suppose the tooth to be soldered to the backing, the backing to the platina cap, and the platina cap to the pivot. It is now to be nicely polished, and is ready for final insertion (d). If the operation has been carried through with care, it will be found to fit the place intended for it in the mouth. The next thing to be done is to barb the pivot wire with a sharp knife, then dry the canal thoroughly, and after heating the pivot and tooth well in the spirit-lamp soften some gutta- percha or Hill's stopping and wrap around the pivot. This is to be carefully warmed until it is quite plastic, when it should be carried as rapidly as possible to its position, forcing it thoroughly into place, and, at the same moment, throw upon it a syringeful of cold water. After it has become hard the surplus of gutta-percha should be cut away with a sharp knife, and all overlapping portions dissolved away with a pellet of cotton saturated with chloroform." The following method, practiced and introduced to the notice of the profession by the late Dr. Marshall H. Webb, of Lancaster, Pennsylvania, though somewhat more difficult of execution than the one recommended by Professor Darby, embraces many points of special merit:— t " Where fracture of enamel has been extensive and its con- tour almost or entirely broken up, it is necessary to prepare the root for the placing of an artificial crown upon it. In all opera- tions upon pulpless teeth or roots, care must be taken that no irritation be induced. " Preparatory to mounting a crown in the manner now to be described, the root should be cut beyond the margin of the gum, and a plain ' pivot tooth' placed upon it by means of 222 MECHANICAL DENTISTRY. wood surrounded with white gutta-percha, which, when made plastic by heat, and the whole inserted, protrudes and presses the gum away from the margin of the root. After this tem- porary crown has been in place a few days, a gold wire (about No. 13) should be accurately fitted in and placed as far up the root as possible. A gold plate, No. 26 (18 k.), should be fitted to the prepared surface of the root, and an opening made in it just large enough for the wire to pass through. The plate and wire should be placed in position and the latter marked with the point of a knife or lancet blade, so that when the wdre is put into a suitable hole made in charcoal and the plate placed upon it, there shall be no difficulty in deciding just where to solder the parts together. When thus fitted, soldered, and then annealed, the gold wire and plate should again be placed in position and more accurately fitted to the root. There should be no movement of the metal while the edges of the plate are being fitted to the prepared surface of the root by the aid of the mallet. After this is done the wire should be cut off to within about two lines of the outer surface of the plate, and the edge of the latter so trimmed as to be on a line with the circumference of the root, and then, with wire and plate in position, an impression of the parts should be taken in plaster-of-Paris or ' modeling composition.' An illustration of a wire and plate, after having been fitted as described, is here given (Fig. 84, a). When this is done and the wire and plate taken from the root and put in place in the impression, a correct model of the teeth and parts adjoining can be made with the gold in the same relative position as when in the mouth. After the model is made, the gold removed from it, the end of the wire wrhich extended outside the root to aid in marking the position of the wire and plate in the impression cut off and filed down to the surface of the plate, a thick, narrow gold backing should be fitted and riveted to a suit- able crown (plain ' plate tooth' with ' straight pins ') and a groove be cut along each side, and, in some cases, near the cutting edge of the porcelain, as illustrated in Figs. 84 and 85. This is done that the parts may then be built out and the porcelain more perfectly secured, and the contour of the palatal ROOT CROWNING. 223 portion restored with pure gold, as shown in the cut with crown in place (Fig. So). After the backing is placed upon the porcelain, it should be attached to the plate with wax and the whole carefully removed from the model, encased in plas- ter and sand, gradually heated, and soldered. The parts, prepared as described and illustrated, may be held by screwing the wire in a hand-vise while the gold foil is being built in place. This can be nicely done with the electro-magnetic mallet, and the crown made ready for insertion by the time of the next appointment with the patient. " A very good and less difficult method of preparing crowns is to back the whole of the porcelain and restore the contour of the palatal portion with fine gold plate (18 to 22 k.), united with correspondingly fine solder. " The apical foramen should be closed with gold. If gutta- percha or oxychloride of zinc be used for this purpose, some of Fig. 84. Fig. 85. b the material may be pressed through the foramen, but with gold the operation can be made more certain and satisfactory. To avoid any exposure of gold, should recession of the gum take place, the edge of the plate ought to be cut away, that the porcelain may be accurately fitted upon the labial portion of the root. " When all is in readiness for placing the crown upon the root, fine barbs should be made with a knife or lancet along the entire surface of the gold wire, a thin layer of white gutta- percha (such as requires little heat) placed around the wires and against the plate; the metallic parts should be heated suf- ficiently to just soften the gutta-percha, and, with the root dried, the whole must be immediately pressed and carefully malleted to place. The surplus stopping should be trimmed off with a lancet a few hours or the day after the crowm is 224 MECHANICAL DENTISTRY. placed upon the root, or when the gutta-percha shall be thor- oughly cooled; the gum will then have been so pressed away that the boundary line between the crown and root can be seen and the edge of the gutta-percha smoothly finished wdth pellets of Japanese bibulous paper, lint, or cotton saturated with chlo- roform. " There is a still less difficult and yet good method of placing crowns upon roots of teeth, and one, too, that does not require so much time as that just described; but the root should be prepared, and a gold wire fitted in it in the same manner. A suitable plain ' pivot' crown, having a hole in it a little larger than the gold wire, should be selected and fitted to the surface of the root as perfectly as possible, and the opening in the porce- lain filled with fine, well-seasoned, hickory wood, which must then be cut off even with the base of the crown, and a hole drilled in the centre, and entirely through it large enough to insert one end of the wire. The surface of the wire should be rough- ened or finely barbed along its whole length, one end placed (not malleted) tightly in the opening made for it in the wood in the crown, and the whole then placed upon the root and finished as above described. " An artificial crown, by whatever method mounted, can be more successfully placed upon a root, and all operations better performed, when the rubber-dam is applied than where it is not used, and it should, therefore, be secured, if the operator can apply it, to the adjoining teeth, and then to the root, before the final fitting and mounting of the crown." Where the deviation from a normal relation of the root to be Fig. 86. crowned is more pronounced, it will become necessary to employ a swaged plate, to which the pin and tooth are attached in the manner described by Prof. Darby. The general form of such an appliance, with the tooth and pin attached, is shown in Fig. 86. Another method of attachment to the root in these cases, by means of a bolt and nut, is shown in Fig. 87. Gold Crowns.—The method of mounting a gold crown in which the attachment to the root is secured by embracing accurately its cervical portion, was first successfully practiced ROOT CROWNING. 225 by Dr. William W. Morrison, of St. Louis, Mo., in 1869. Four years 'subsequently, the late Dr. B. Beers, of California, took out letters patent covering a process which did not essentially differ from the former, except in the use of headed screws as an additional means of support. Dr. Morrison thus describes his first case in Missouri Dental Journal, May number, 1869 :— " Miss W. came to me with a first left lower molar decayed to the extent that the entire lingual and a greater part of the labial surfaces below the gum were removed. The roots were filled properly with gold, and the crown had been filled several times ; the last time the crown was built up in good style, but the two walls being of such a shape that they could not be made self sustaining, I took a natural tooth corresponding as Fig. 87. nearly as possible in size and shape to its fellow of the opposite side, and imbedded its roots in plaster to make a model from which to get a metallic die over which to swrage a gold cap. I used a thin piece of pure gold plate, cutting it at the corners, giving but a slight lap for soldering after it was perfectly fitted to the die. I then fitted this cap accurately to the remaining portion of the tooth in the patient's mouth, allowing it to extend under the free margin of the gum quite to the alveolus, which was about the thirty-second part of an inch below the margin of decay. After soldering a bar across the cap from the lingual to the labial surfaces, it was finished and polished at the lathe. I then prepared the patient's mouth as usual for filling; made a thin paste of oxychloride of zinc, filled the cap and pressed it to its place; the superfluous cement was crowded 16 226 MECHANICAL DENTISTRY. out of the cap and removed at the margin of the gum. I had the pleasure of seeing that tooth to-day, nearly four months after the operation, and had the gratification of seeing and hearing it pronounced a perfect success." The following is a description of Dr. Beers' method (illus- trated in Fig. 88), reproduced from a printed circular in Dental Cosmos, September, 1880. After taking an impression of the tooth or root, he says : " Take a strip of flat gold, and strike with a punch in the centre of it, into a piece of lead. This will give the front form of an incisor, lateral, or bicuspid. Then anneal the gold, and bend the two ends around the tooth requiring a crown; when properly fitted, solder the ends together. Then adjust the bite by hollowing out with a half- round file, so that it articulates properly with its antagonist. Fig. 88. Then bend a piece of thick, flat gold, with half-round pliers, to suit the form of tooth required, and solder securely on the top of the gold tooth and finish up." Thus Dr. Beers formed his crowns. They were fastened to the roots by inserting headed screws into the canals, filling the gold crowns with some cement (oxychloride of zinc), and forcing the crown over the root or broken tooth to place. Dr. Beers says, " In some cases it is not necessary to use the screws, as the gold crown fits so closely and firmly to the root that the cement is found quite sufficient." He does not seem to have been in the habit of specially dressing off his roots, or even of removing standing portions of broken crowns, but fitted the gold caps over the whole. The following is an abridged account of Dr. Eugene S. Tal- ROOT CROWNING. 227 bot's method of forming and attaching a gold crown, as given by Dr. Dexter. The several parts are illustrated in Fig. 89. A band is made and fitted to the root, extending Fig. 89. nearly to the alveolar process. Across this band .p^^ on the inside, and at a distance sufficient to leave a space over the root when the band is in position, is soldered a floor of gold, having holes to correspond with the pulp-canals beneath. These canals are drilled out to receive wires, which are placed loosely therein. The band under the floor is then filled with gutta-percha or a cement, and forced to place on the root, the wires projecting through the holes in the gold floor. After cooling of the filling the wires are removed, and their places taken by headed screws, which securely fasten the whole to the root. The crown may be completed by filling the band with gold, or a gold crown may be struck up and slipped either outside or inside the band, being fastened with gutta-percha or a cement. One of the most complete and practicable methods yet adopted in croAvning a root with gold is that devised by Dr. C. S. Case, of Jackson, Mich., and published in Dental Cosmos, February, 1885. Omitting such portions as are not descriptive of the process, the account of the method is here given in full:— " The mechanical preparation of the root should be the same, in my opinion, as for any crown (excepting the Biittner) that is intended for a ferrule to telescope over it,—i. e., after the gum has been separated from its attachments to the root, all that portion which is intended to be received within the ferrule should be made in the form of a straight tenon, having parallel sides. For this purpose I use a short, sharp, sickle-shaped scaler, drawn so as to take an oblique direction along the side of the root. " The importance of entirely removing the dovetailed shape of the root cannot be overrated, and I think the neglect of it is one of the principal causes of failure, for, if the crown is made to pass over the enlarged end, it must needs leave a space be- yond, between it and the root, that is difficult, if not impossible, to close by the most thorough burnishing. This space soon 228 MECHANICAL DENTISTRY. fills with decomposed blood, serum, and broken-down tissue, causing subsequent disease, which must proportionately impair the perfection of the operation. It is not necessary to shape the end of the root flush with the margin of the gum, as is com- monly the practice, in order to remove as far as possible the enlargement of the natural crown, because all that can be left gives additional strength to the new crown, and is often suffi- cient without the aid of screws or other appliances. It is not a difficult matter to remove the enamel and a peripheral portion of the dentine, with sharp sickles, side-cutting hoes, and disks. In fact, it is not an uncommon practice with me (and doubtless with others) to telescope a hollow gold crowm over a tooth that has become too much disintegrated to fill, but still has a normal pulp. "After the root has been prepared, I prefer to obtain not only a measurement—the usual method—but an exact pattern of it, and dismiss the patient, to continue the work at my leisure in the laboratory; so that at the next sitting I shall have a tube that will at once pass over the root, and fit into all its irregulari- ties, with no need for alteration. "Around the prepared root pass a piece of fine, soft, or annealed wire. Surgeon's silver suture wire is best, because it retains whatever shape is given it without the slightest recoil. Carry the loop beneath the margin of the gum, on the palatal or lingual side, with a pair of gold carriers, the same as you would a silk ligature when putting on the rubber-dam. Now twist the ends together on the labial side with a pair of pliers, and burnish the wire into conformity with the irregularities of the root. Before removing the loop it should be so marked that it will indicate the relative position it took in the mouth. This can best be done by turning up the free ends of the wire, as shown in Fig. 90. Then its removal from the root should be accomplished with the greatest possible care, so as not to disturb its peculiar shape. If this cannot be done with comparative ease, it will indicate an enlargement at the base of the root, that must be removed before proceeding further. Having obtained a perfect pattern of the root (see Fig. 90), I dismiss the patient; and when opportunity offers I cut a form ROOT CROWNING. 229 on the end of a piece of hickory, that will pass through the wire loop so as to exactly touch its inside circumference, and yet not disturb its original shape (see Fig. 91). To guard against this the following plan has been suggested: Warm a strip of base-plate wax; place it within the wire loop, and with a hot wax-knife cover the inner half of the wire (see Fig. 92), and then invest in plaster, which, when hard and the wax is Fig. 90. Fig. 91. Fig. 92. Fig. 93. removed, is to be trimmed top and bottom flaring from the loop, as shown in Fig. 93. This will facilitate the shaping of the hickory form and prevent disturbance of the guide-loop which should always be, as shown in the cut, near the bottom or cervical aspect of the plaster shell. In my practice I have not found this necessary, as I can shape the wooden form as soon as I could make the matrix, and preserve the shape of a loop of large or medium-sized silver suture wire with little Fig. 94. Fig. 95. Fig. 96. difficulty. I hold the loop carefully against the stick, and with a sharp pencil outline its inside circumference. I then cut rapidly down to this with a coarse file, and finish with a fine one, being careful whenever the loop is tried to use no force. ''A strip of gold plate should now be cut long enough to reach around the form, and wider than the length of the desired 230 MECHANICAL DENTISTRY. crown; the approximating edges beveled and drawn together by a loop of annealed iron wire (see Fig. 94); then removed from the form and soldered. If it is desired that the body of the crown shall be larger than at the cervical portion, the strip of gold plate should be cut crowning, so that when passed around the form it will flare from it, touching only at the part that is intended to fit the root. After soldering, the ferrule should be again returned to the form and more perfectly fitted, and the edge that is to pass beneath the gum made thin, polished, and shaped so as to conform to the shape of the border of the alveolus. If the work has been done carefully, this ferrule will telescope perfectly over the root. It should now be forced to the position it is intended to occupy when finished, and an impression taken in plaster of it and the adjoining teeth. If the ferrule does not come away with the Fig. 97. Fig. 98. Fig. 99. plaster, remove it from the root, and place in position in the impression. Before dismissing the patient for the second time, secure a perfect' bite ' of the place in wax. " A model in plaster from the impression obtained will show the ferrule in the same relative position it occupied in the mouth. Draw a line across it even with the cusps of the ad- joining teeth (see a, Fig. 95); remove from the model, adjust the wax ' bite,' and make a plaster articulation. By the aid of this, make a model of the crown in wax, or modeling com- pound (see x, Fig. 96), to be used as a guide in shaping cusps upon the end of the wooden form (see Fig. 97). After which the shoulder should be filed back, so that the ferrule, when adjusted to the form, will stop at a place that will give the proper length to the crown, when the free end of the ferrule is turned down ROOT CROWNING. 231 to form the cusps, as will be described. The guide to this will be the mark that has been made upon the ferrule, before removing it from the plaster model, to be governed always by the wax model of the crown. That is, the articulating teeth may strike into the space in such a way as to preclude making the buccal cusps even with those of the adjoining teeth. In forming the cusps, cut Y-shaped pieces from the projecting end of the ferrule, and turn down one lap at a time, fitting the edges in turn with hammer and file (see Fig. 98). " To facilitate soldering, a thin piece of platinum can be easily fitted over the wooden cusps within the crown, and the whole invested in plaster and asbestos, so that the platinum lining is crowded to place, and only that portion of the crown exposed that is to be soldered. After soldering, replace the crown upon the plaster model, and correct any deviation from a perfect ar- ticulation. Finish and polish upon the wooden form (see Fig. 99). When this is inserted upon the root in the mouth, I think one can reasonably expect that no other change will be necessary. "Before final adjustment, a small hole should be drilled through the articulating portion of the crown, for the escape of surplus cement; the hole to be subsequently filled with gold foil. With the root already in a healthy condition, one has occupied at the chair not more than two hours of time, as follows: One hour at the first sitting, to prepare the root and obtain pattern; one-half hour at the second sitting, to adjust the ferrule and take the impression and 'bite;' and one-half hour at the third sitting, to adjust the crown; and this is made possible by the fact that everything has been fitted outside the mouth." The author, in February, 18S4, number of Archives of Dentistry, described the following method of crowning with gold. Such portions as relate to the preparation of the root and forming the band, which do not differ from the methods usually em- ployed in these cases, will be omitted here; stating, however, that adequate anchorages should be secured, either by enlarging the openings into the pulp-canals or by pins cemented therein and extending into the body of the crown. 232 MECHANICAL DENTISTRY. The band being placed in position in the mouth by forcing it over the neck of the tooth, and well under the free margin of the gum, but not far enough to impinge upon the connective tissues, the patient should be directed to close the teeth to ascer- tain if the band is of the right length, in respect of articulation ; a narrow space between its edges and the opposing teeth being necessary, as will appear hereafter. The band or ferrule is now permanently attached to the roots by the use of amalgam, which should be carefully and thoroughly packed around the metallic supports projecting from the pulp-canals into the body of the crown, and also into any undercuts provided for purposes of attachment, continuing the process of packing until the tube is thoroughly well filled to a point the fourth or sixth of a line from the open end, thus leaving a narrow rim free to be turned over upon the body of the amalgam at another and final sitting. With particular instructions that the use of the teeth on that side of the mouth should be strictly avoided, the patient may be requested to return in two br three days, by which time the amalgam will be sufficiently hard for the subsequent manipulations. The operation is completed by first turning the free edge of the gold band over upon the amalgam body, and this may be accomplished with serrated pluggers and the mallet, the over- lapping portion being well cleansed and scraped after applying the rubber-dam. The serrated points used in tamping or forcing the free edge down upon the amalgam will stipple the exposed surface for cohesion with the gold to be subsequently used. A sufficient number of retaining points are now made by drilling into the body of the amalgam at suitable points. These being carefully and compactly filled with gold foil, the process of impaction is continued until the exposed surface of amalgam is covered with a layer of sufficient thickness, and the required configuration of the masticating surface obtained, adding enough to effect a practical articulation with the an- tagonizing tooth or teeth of the opposite jaw. It will be found that the gold used for capping will cohere readily with the overturned edges of the band, securing absolute continuity of structure—a complete box or cap of gold without seam or joint ROOT CROWNING. 233 With comparatively little labor, the work of final dressing and polishing can be accomplished, and the operation is then completed by forcing the marginal portions of the cap at the gums into close contact with the cervical walls with a bur- nisher or other suitable instrument. Dr. J. McMillen, of Kansas City, Mo., recommends the follow- ing ingenious method of casting a cap, or articulating face, for gold crowns:— " Take a piece of sound charcoal, cut out a small square, into which run a somewhat watery mixture of about equal parts of plaster and pulverized pumice stone. Select a tooth of the de- sired shape and size, and set it in the plaster mixture, sinking it as deeply as will equal the desired thickness of the cap when cast. Let the tooth remain until the plaster is well hardened, when on removing it the impress will be distinct and smooth. Dry the plaster thoroughly, melt the gold on the surface of the coal, tip the piece of coal slightly, when the molten gold will run into the mold. While still melted, place the face of a hammer or other smooth body upon the molten mass, and a crown-cap is formed thick enough to stand the wear of mas- tication, or to admit of considerable dressing, if necessary, to perfect the articulation. The band is formed in the usual way, when the cap may be placed inside the band and allowed to telescope to suit the articulation. " If a long crown is called for, the cap may be set upon the band, and soldered fast to this position. This cap is thick enough to admit of grinding to correct any defects in articula- tion, after the crown has been set. These caps can be very quickly made of any desired fineness of gold and will be found very durable." The following method of securing an outline of the dimen- sions and contour of the end of the root for the adjustment of a gold band is recommended by Dr. John G. Harper in the December (1884) number of Archives of Dentistry. It cannot fail, with careful manipulation, to secure accurate results, and may be used to advantage in connection with all banded or ferruled crowns. " Take steel wire No. 27, annealed, pass it around the root, 234 MECHANICAL DENTISTRY. previously prepared, twdst the wire with your pliers until you have drawn the wire snug, then carefully remove, and you have a ring the exact shape of the root at the point to be occupied by the band. The next step is to lay this ring on the smooth end of a block of close-grained wood ; with one blow of a flat-faced hammer drive the ring into the wood, carefully remove the ring, and you have an exact model of the circumference of the root. Before laying aside your ring you can make it perform one more office by laying a piece of gold plate on the block of wood, lay the ring on this plate and strike the ring with your flat-faced hammer; this will cut out the cap to be soldered on to the band. " To make the band, simply bend it until it fits into the groove in the block of wood. The process of making crowns has been described so often that it is useless to relate all the steps in the process." Dr. Barrett, of Buffalo, N. Y., has also suggested a very in- genious method of accomplishing the same result, attributing the device to Dr. H. A. Baker, of Boston. The former, in describing the process, says :— " Copper is rolled down quite thin, and a band three-fourths of an inch wide wrapped about the root of the tooth and forced up under the gum. A ligature is passed around both, the cop- per band is burnished down, and the ligature drawn tight. This copper band will now fit just about as we want the gold band to do. Plaster-of-Paris is then inserted in this, forced up against the end of the root, and permitted to set. Take it off, and if you use Babbitt metal a piece of paper wrapped about it will lengthen it out sufficiently, when the melted metal may be poured into it, and thus a perfect model of the end of the root will be secured. That part that is inserted in the copper is the exact reproduction of the root of the tooth. The model will, perhaps, need a little dressing down with a file, when the gold band may be fitted about it and soldered, thus avoiding the necessity for the annoying and painful trying on in the mouth." Gold Crown Faced with Porcelain,—The subjoined method of attaching an artificial crown to a root was originally introduced ROOT CROWNING. 235 to the notice of the profession, in 1872, by the late Dr. Marshall H. Webb. The following is a description of his more recent and perfected method of operating, which, while it necessitates great care, dexterity, and delicacy of manipulation, unquestion- ably possesses, in an exceptional degree, the important advan- tage not only of security of attachment, but of indestructibility, the union with the prepared surface of the root being effected by direct contact of impacted gold:— " Building crowns of gold upon roots of teeth and facing them with porcelain makes the most secure and satisfactory though difficult operation. "After preparing the root, closing the foramen with gold, and cutting away the irregular or projecting edges to within about half a line of the margin of the gum (leaving this much to aid in applying the rubber-dam), a gold wire, No. 13 or 14, with a Fig. 100. fine, sharp thread cut upon it, should be accurately fitted in the pulp-chamber to near the apical foramen. To the platinum pins of the porcelain selected for the case a cylinder or tube made of gold plate should be fitted, and, after it is opened (Fig. 100), riveted and then closed, placed in plaster and fine sand, and carefully heated and soldered. A thread must then be cut in the cylinder corresponding to that upon the wire to which it is to be attached. This is done that the crown may be more se- curely placed upon the root than by the method described by the writer in the Dented Cosmos, June, 1873. The end of the gold tube next the cutting edge of the crown may be beveled and a slot made in the wire at that part, so that the cylinder will be prevented from turning, while still greater strength is added by impacting gold into the open part, thus spreading the 236 MECHANICAL DENTISTRY. end of the wire. A groove should be cut with a corundum disk in each side (6), and sometimes along the cutting edge of the porcelain, into which gold foil is to be placed, to secure greater strength and permanency. " When all is in readiness for the operation, the rubber-dam should be applied to two teeth each side of the root and to the root itself. The ligature of waxed floss silk should be placed twice around the root, tightened, and pressed well to place with a burnisher, the ends of the silk wrapped twice, as in tying a surgeon's knot, and the ligature then attached to the ring at the end of an elastic rubber-dam holder and held just below the edge of the slightly upraised lip, so that, when the holder is fixed to a tie put around the patient's neck, there shall be constant tension upon the ligature. After this has been done the root should be trimmed down with corundum wheels or cones to the ligature, although not close enough to displace it. The porcelain should then be so fitted as to leave half a line of space to be filled with gold (as at c) between it and the root, after the wire has been placed in the cylinder and screwed into the root. In placing the parts in position, a little oxychloride of zinc, nearly the consistency of cream, should be placed in the root next the gold that closes the foramen, and the gold wire at once put in this and screwed securely to place. After the oxychloride of zinc has crystallized, sufficient of it and of the dentine should be cut away with small burs to secure good anchorage for the gold now to be placed as perfectly and solidly as possible around the wire, to and over the margin of the root, along the gold tube, into the grooves made in the porcelain and between it and the labial margin of the root (c). This narrow line of gold need not be made visible when the operation is completed. The gum should cover it. While the gold is being placed around the wire in the root, the porcelain can be turaed a little to one side upon the gold wire till the cylinder is reached and restoration of the contour of the parts commenced. All the gold should be cohesive and impacted by the aid of the electro-magnetic mallet, with which the surplus foil can easily be trimmed away from the margin of the root as placed upon it, and the form of the crown so niceLy carried forward that but ROOT CROWNING. 237 little dressing is afterward necessary. The gold should be filed even with the margin of the root, and finished with narrow strips of fine emery cloth at and near that point, while the rub- ber-dam is yet in place; after this is removed the gold should be so cut away as to allow proper occlusion of the teeth, and a little space should afterwards be gained by very careful wedging for the trimming and finishing of the gold along each proxi- mate surface separately." The form and relations of the several parts entering into the construction of a crown by Dr. Webb's method are shown in Fig. 100. The following is Dr. Henry Weston's method of attaching and contouring a porcelain-faced crown with the use of either gold or amalgam, at the option of the operator:— " This plan comes entirely within the province of the opera- Fig. 101. Fig. 102. Fig. 103. Fig. 104. tive dentist, requiring only, perhaps, half an hour's mechanical work, and that of the simplest character. When finished prop- erly, there is simply a gold or amalgam filling faced with por- celain. This crown represents on its labial surface the ordinary plate tooth, the lingual or palatal surface being concaved in such a manner as to afford the largest amount of working room without impairing its strength at any point. The pins are so imbedded in the thickest part of the crown that it is not liable to be weakened by grinding. Fig. 101 represents the crown. "The pin is made of hard platinum or platinum and iridium, and is spear-shaped and notched on both edges to give firm- ness to its anchorage. The backing is of the same metal and strongly soldered to the pin. Fig. 102 represents the pin. "The operation consists of taking a cast of the root and of the adjoining teeth to be used in the selection of the crowm, and 238 MECHANICAL DENTISTRY. with reference to proper articulation. This may be done either before or after the preparation of the root for the crown; if before, cut as much from the cast as you propose to remove from the natural root. The preparation of the root for the reception of the crown consists of the removal of that part of the tooth to be replaced by the porcelain. If a large portion has to be cut away, coarse burs may be used at first, but the finish- ing should always be done with the finest and sharpest. Fig. 103 shows the root at this stage. " The enlargement of the pulp-canal is next in order, and is most readily accomplished by the five-sided reamers used with the dental engine, and which are represented in The S. S. White Dental Manufacturing Co.'s list as Nos. 146, 147, 148. The pointed fissure burs, Nos. 171, 172, 173, will also be found use- ful for the purpose, and for shaping the retaining points and undercuts, cones Nos. 25 or 26 and 27. The canal must be sufficiently enlarged to allow space for packing gold or amalgam securely about the pin. Good judgment is required at this stage of the operation, as to the removal of neither more nor less dentine in the enlargement of the canal than is necessary. Fig. 104 shows the root prepared for the reception of the pin. " Fig. 105 represents a transverse section showing the position of the pin in the root. The grinding of the crown to the root requires but little labor, and the fitting may be done directly on the natural root, or on a cast taken after the root has been prepared. It must always be done with the utmost neatness and pre- cision. When fitting, the crown can be held in position by a cone of wax inserted in the root. " Next comes the adjustment of the pin to the root and crown. After punching holes in the backing to receive the pins of the porcelain crown, bend the pin with small, flat-nosed pliers, so that when in its proper position there will be a uniform space around its entire surface. Secure the tooth and pin together with a cement of resin and wax; invest in plaster and sand, and solder with fine gold solder. It has been my practice of late years, Fig. 105. ROOT CROWNING. 239 when preparing the root, to leave just a line of enamel around its entire circumference, thus securing a joint clear of the free edge of the gum, especially when gold is used. The propriety of this method may be questioned by some, but my success in this particular justifies my belief that it is the best plan where feasible. What dentist ever cut away sound dentine or enamel for the purpose of concealing the margin of his filling under the free edge of the gum? The cases are analogous and the comparison fair. If gold is to be used as the attachment, the rubber-dam is indispensable. When amalgam or cement is used the rubber-dam is of decided service, but it may be dis- pensed with by those who prefer other methods of keeping out moisture. When gold is to be used, the root having been pre- viously properly treated and everything in readiness, and the rubber-dam in place, put upon the point of the pin a pellet of phosphate or oxychloride of zinc, the size of a No. 7 or 8 exca- vating bur; now press the pin and crown carefully to their exact position into and upon the root, and with a delicate but blunt-pointed instrument, thin enough to reach the end of the canal, pack the cement firmly about the pin. The object in using the cement is to secure the pin in its place during the first introduction of the gold. By using the hot-air syringe the cement will harden in two minutes. Close the opening of the canal about the pin with a rope of bibulous paper, and attach the crown to the root and adjoining teeth on either side with soft wax; see that the joints are exact in every particular, as after the next step mistakes are not easily remedied. " Paint the joint from the labial side with cement mixed to the consistence of cream. Cover the labial surfaces extending over the cutting edges of the porcelain crown and adjoining teeth to the thickness of three-eighths of an inch with carefully mixed impression plaster. When hardened the plaster may be cut from the cutting edge of the crown, and the wax and the paper removed. Now paint the palatal side of the joint with the cream-like mixture, applied with flattened pulp-canal plug- gers. Harden with hot air, and the case is ready for the gold. This will be best understood by old operators, who formerly used gold for filling pulp-canals. The beginning should be 240 MECHANICAL DENTISTRY. made with soft, semi-cohesive No. 4 gold foil, cut into f-inch strips and rolled into fine ropes. Cut this into J- to f-inch lengths, and thoroughly pack one at a time about the pin. Other numbers of gold foil may be used, but the finer and smaller the gold at this stage of the process the better, in order to avoid choking the canal. The instruments should be finely serrated, well tempered, and bent and shaped at such angles as to reach all parts of the canal. With the foundation well se- cured, the gold may now be annealed, and as before condensed, one piece at a time. As the work advances heavier ropes can be used, but they must not be cut longer. Still heavier gold may be added as the canal enlarges, and from this point to the completion of the operation the various grades and forms of cohesive gold are applicable, as blocks, cylinders, mats, etc. When finished, and the exposed dentine and enamel are all covered with cohesive gold and porcelain, the result will be a fac-simile of Figs. 106 and 107. "If preferred, the cement in the labial joint may be dispensed with, and the space between the crown and the root carefully filled with gold after the removal of the plaster covering all of the exposed root, showing only a fine line of gold at the margin of the gum. The operation iust de- Fig. 106. Fig. 107. ., , & ,. . .* , , J , scribed may be simplified and perhaps improved upon in a practical point of view, without in the least sacrificing its strength, beauty, or durability, by fill- ing a portion of the canal around the pin with amalgam, leaving room only for a secure foundation for the gold. There is no question about the propriety of this practice, and no doubt about the results, which are probably in favor of the amalgam. In most cases, its easy adaptability to the walls and undercuts adds greatly to its value. When the canal is neces- sarily small, owing to the size of the root, the cement at the end of the pin may be dispensed with, and the canal filled half or two-thirds full of amalgam, soft enough to allow the pin to pass readily through it to its proper position. After having been secured with plaster as before described, the excess of mer- ROOT CROWNING. 241 cury may be readily taken up by packing thoroughly about the pin more amalgam with the mercury previously expressed —continuing the operation as before described. Amalgam for the entire attachment answers all practical requirements fully, and when we consider the ease with which this operation is thus performed, compared to that with gold, the time and labor saved to the dentist, and the advantage in point of cost to persons in moderate circumstances, the odds are largely in favor of this material. The selection of the proper amalgam for this pur- pose is of the greatest importance. It should be full, hard, and strong, hold a sharp, thin edge, and keep its color in the mouth. While the many preparations in the market may answer the purpose for which they are intended, not one in five possesses these requirements. Where amalgam is used' exclusively for the attachment, the greatest accuracy should be observed in the proper articulation of the crown before introducing or packing it, and in removing carefully all excess, and the patient should be cautioned against biting on the crown until the following day. The manner of preparing the crown, pin, and root, and filling the latter, is the same as before described. Use a trifle more cement at the point of the pin, and apply more on the palatal side of the joint to prevent a dark line showing. It is claimed that amalgam produces dark joints and unsightly dis- coloration, and it is in such places that the superiority of gold asserts itself over all other materials. " If the attachment is to be made entirely of any of the various cements, fill the canal half or two-thirds full, press the pin through the cement to its place, and pack tightly with small blunt-pointed instruments, slightly oiled to prevent sticking. With a new mixing fill and cover the joints; harden with hot air; remove enough cement from the canal to secure thorough anchorage; mix more cement thicker than the last; finish and harden as before. In every case the greatest care is required in the proper articulation. Instead of making this porcelain tooth assume the burdens of its healthy living neighbors, its labors should be lightened. Careful articulation alone does this. "Always insist on seeing the patient in a few days if possible. Five or ten minutes' work at this time may enhance the value 16 242 MECHANICAL DENTISTRY. of the operation tenfold. The use of articulating paper is in- dispensable in securing the desired articulation." The author is indebted to Dr. J. E. Low, of Chicago, 111., for the following descriptions of an original method of crown re- placement, for which he claims exceptional advantages. The account of the process, with accompanying illustrations, was prepared, by solicitation, expressly for the present edition; and, also, the article on " Bridge-work," introduced under its appropriate head in another place. The " New Low Crown " is thus described by the inventor:— " This crown is the result of an effort to overcome the many objectionable features to be found in other crowns in use at the present day. "Having had an extensive experience in crown work, with a thorough knowledge of all crowns in use, and with the many letters now before me from various parts of the country, con- taining testimonials to this effect, I think I can justly claim that this crown is nearer perfection than any other before pre- sented to the notice of the Dental Profession. I am aware that the average dentist does not differ from the rest of humanity at large, in the matter of changing their mode of operating, and when any new improvement is presented to them, they at once begin to see what objection they can raise against it, instead of recognizing its good qualities and advantages over others. As I have had a good opportunity to know most of the objections raised against the crown in question, I think it best here to mention those of importance and show how incor- rectly they have been drawn. " Now, I do not wish the reader to think for a moment that I object to criticism, providing it is just, for this would assist me in regulating what imperfections there might be to the benefit of all. One of the most common objections raised by those who have never used the crown, is that the instruments cut away too much tooth substance in preparing the root, and the walls of the tooth are thereby weakened. " Then, again, some claim that it is necessary to have a band around the tooth to prevent it from splitting. The other ob- jections are not of importance enough to notice. I will now ROOT CROWNING. 243 proceed to set a crown by this method, and if in so doing, I am clear and comprehensive, I think all will agree with me in saying these objections are not well founded. " By carefully looking over the case of instruments represented in Fig. 108, you will find there are seven in number, instru- FlG. 10s. ment Xo. 1 being the smallest. This instrument can be used in more cases to advantage than any other. Almost all of the laterals, and nearly all the bicuspids as well as all badly de- cayed molars, when so decayed that gold crowns cannot be 05199994 244 MECHANICAL DENTISTRY. used, and, in fact, any tooth that is generally set down as beyond restoration, can be crowned successfully wdth this instrument. " We now have before us, Fig. 109, a central incisor '■ badly decayed. The first step to be taken to crown this root with a strong and serviceable crown, is to cut or grind even with the gum what tooth substance remains. We start off with the supposition that the root is in a healthy condition; if not, it must first be treated, and made so, as this is the first consideration in the final result of a successful operation. The next step is to select the instrument in accordance with the size of the opening in the root to be crowned. The larger the opening in the root, the larger the inside or centre cutters must be, and the narrower the cutters that bevel and prepare the end of the root. The reason of this is that the space is nearly all taken up by the inside cutters, in order to reach and cut away the decayed tooth substance, and prepare the root to properly receive the step-plug with bevel cap, which covers the end. " We have seven sizes of instruments to select from, and when properly selected, no tooth substance that ought not to be re- moved will be, cutting as they do the least where the tooth is smallest, or, in other words, cutting the opening in the tooth in the same shape as the root; tapering. " These cutters leave the root in the i " shape of Fig. 110 with graded step. We next select the graded step-plug as seen in Fig. Ill, the same number as the instrument, which will perfectly fit the opening, and cover the end in a beveled saucer shape, and by its attachment when cemented, makes a combined union of strength, un- equaled by any other crown, and thus it is made impossible for the root to split. In Fig. 112 we have the step-plug placed in position. "After placing the plug in position, an articulation of wax, and an impression of the space to be supplied, and a few adjoining teeth, are taken in plaster-of-Paris. Before taking the impression, ROOT CROWNING. 245 be careful that the pin which extends from the cap of step-plug for the purpose of removing is free from all roughness (a rough- ness that is sometimes left in the cutting of the plug), as this is liable to break the plaster when removing the impression from the mouth. I generally file the step-plug on a slant from the labial side to the centre, so that there will be no mistake in re- placing the step-plug into its proper place in the impression. After placing the plug back in the impression, if necessary, take a thin, heated spatula, and stick the plug fast with a little hard wax on the outer edge, so that it may not be disturbed in pouring. Be careful not to get any wax on the part of the plug where you do not want solder to flow in. Now varnish the cast in the usual way, but do not touch the plug with the varnish. Next, pour with plaster and sand, asbestos or pulver- Fio. 113. Fig. 115. ized pumice stone, any one of which will do. After the plaster is thoroughly hardened, carefully cut it away in the usual manner. Place the articulation in the articulator, and pour in the usual wray. The tooth is selected, and we proceed to back the same in the following manner : First, grind and fit the tooth to the cast and cap to suit you; then cover the entire inner surface with thin platinum, the thinner the better. Bur- nish close to the surface of the tooth. Then use 28 gauge platinum for a backing down to where the tooth is ground out to fit the step-plug, and bend the pins down to hold the two pieces of platinum tight to the tooth. We now have Fig. 113 representing the tooth as it appears backed ready to place in position. Next place the tooth in position in the cast, cover 246 MECHANICAL DENTISTRY. with plaster and sand and solder with gold coin. After fin- ishing and polishing, the crown is ready for adjustment. Moisten the step-plug and cap with cement, and with the little roter, seen in Fig. 114 or in the case, gently press the crown up in position, and we have the crown completed as seen in Fig. 115. "Should you desire a cheap crown, you can solder with block tin. After experimenting with various metals, I have succeeded in making a step-plug or tip of platinum and nickel that is as strong as steel and cannot be melted. In the above description I have given my way of making the crown. This given in detail seems like a long, tedious method, but it is very short; and as I always keep a laboratory man, but very few minutes of my time are consumed in the making and setting of a crown, not exceeding twenty minutes in any case, as I only prepare the root, take an articulation and impression and, with the shade of the tooth, hand in to the laboratory man. When my patient returns, providing the crown is not made while I am doing some other work for the same party, it takes me from ten to fifteen minutes, counting the setting of the cement to adjust the crown. " The above is my manner of setting the crown in order to save time at the chair. Should I perfect the crown myself, I should take a shorter way, viz.: after preparing the root with the instrument and placing the step-plug in position, my tooth is selected, ground, and arranged in the mouth, after which I back the tooth as before described; then soften a little piece of hard wax, made of resin, gutta-percha and beeswax. I warm and stick a small amount of this to the backing of the tooth, and place the tooth in position, in the mouth, perfectly im- bedding the top of the step-plug in the wax. Great care must be exercised here to have the tooth in the position desired, in pressing the tooth and wax against the plug. I next care- fully remove the wax and tooth, and with pliers remove the step-plug and place in the impression just made. Then with a heated spatula stick the tip and wax together; pour in the usual way, and in a few moments it is ready to solder. In this way a crown can be set easily in one hour's time. ROOT CROWNING. 247 " If you wish to crown a bicuspid or molar tooth, your first step is to grind what little tooth substance there may be down even with the margin of the gum and then use your drill. In drilling, instead of following the nerve cavity direct, which would leave the instrument a little diagonal, hold the instru- ment perpendicular. This leaves the upper portion of drill to the outer wall of the root, and brings the lower portion of drill to the inner side of the root. There would be danger of puncturing through the wall of the root, should you continue going deep enough, but there is no need of going to such a depth. Then take the No. 1 cutter, which will invariably be the instrument to operate upon all the bicuspid and molar root canals, and after carefully cutting to the depth desired, the root is ready for the introduction of the first step-plug of same size. We now drill one other root in the same manner, and, after placing the step-plugs in position, take an articulation and impression, remove the plugs and place in the impression; pour and separate, and place in the articulator as described before. We now have an exact impression of the root to be crowned, with a few adjoining teeth. " Next take a thin piece of platinum and make two perforations for the pins on the ends of the step-plugs to enter; press the platinum down over the root and burnish close to it; then remove the same and trim by the marks made in burnishing to the exact shape of the root. Place the platinum on the root again, and we are ready to select our tooth. This should be made the same as is used for bridge-work, with gold cusps, so there can possibly no breakage occur. Now place the tooth in position in the articulator and hold in place with wax. Encase in plaster and sand, and fill in and solder up with coin gold; or, if you choose, block tin can be used. After polishing and burnishing, you have a strong, durable crown, only equaled by the natural tooth, ready to be adjusted. " The setting of a bicuspid is similar to that of the molar. In setting a bicuspid we seldom use but one step-plug. " In Fig. 110 we have the root cut ready to receive the step- plug. 248 MECHANICAL DENTISTRY. " In Fig. 117 we have the step-plug with the platinum attached, which covers the entire tooth surface. " In Fig. 118 it will be seen that the cap to the step-plug goes below the surface of the tooth, leaving tooth substance all the way around ; but the platinum that is soldered to the step-plug rests on the tooth surface. " In Fig. 119 we see the crown ready for adjustment. " Fig. 120 is the tooth after it has been adjusted. " These plugs can be used to great advantage in varied dental operations. There is nothing equal to them for restoring broken and decrepit teeth to their original usefulness. I use them exclusively in bridge-work. They make a firmer, stronger, and more durable ground-work for bridging than any other method I have ever discovered. In badly-decayed molars, where there is not sufficient tooth substance to hold a gold crown for bridge, I always place one of these plugs in the Fig. 116. Fig. 117. Fig. 118. Fig. 119. Fig. 120. root, which makes a solid foundation. If the pin on the end of the plug for removing is not long enough, it can be very readily lengthened, by soldering a piece to it without danger of injury or melting the same. The plugs are made of a perfectly non- corrosive metal, although the color might indicate otherwise. They are strong as steel, and cannot be melted by any heat from an ordinary blowpipe." A process of attaching porcelain crowns to the roots of teeth by the use of steel screws, originally introduced to the notice of the profession by Dr. George T. Moffat, of Boston, Mass., but more recently and particularly described by Dr. E. W. Foster of the same city, is worthy of a place among the best operations of this kind by reason of its simplicity, security of attachment, comparative inexpensiveness, and its practicable application to all classes of teeth. Dr. F. thus describes the method:— ROOT CROWNING. 249 "Among the principal features of this method is the steel screw in place of the steel pin, as first applied, and which unites the crown to the root in the most perfect and absolute manner. The inner head of the screw (Fig. 121, a) is a concave or half globular, and completes the principle of a ball-and-sncket joint between itself and the circular cavity in the posterior part of the crown, seen at b, in a vertical section of the same. This, it will be observed, permits of an automatic adjustment to the root, but more so in lateral directions, a fact of great import- ance and convenience where the root is out of its normal posi- tion, as is frequently the case, especially as regards the anterior teeth. Where the root is sound and the joint close, a few layers of soft gold foil are placed between the crown and the root. After a careful and final setting of the screw, an impervious Fig. 121. Fig. 122. joint is thereby obtained—one perfectly odorless and highly antiseptic to the root for an indefinite period of time. " The prejudice against the old and odorous varieties of crowns is well sustained by all persons of intelligence and refinement. " The front view of an incisor crown thus set is shown at a (Fig. 122). The posterior cavity in the crown, over the screw- head at b, is filled with gold, or other material, and finished flush and smooth with the surface. Where gold is used, which is generally preferable, the retention of the first pellets is greatly facilitated by the previous arrangement of a few layers of adhe- sive gold foil under the head of the screw, whose overlapping edges serve admirably the purpose intended. " Oxychloride of zinc or gutta-percha would be indicated in cases where the root was hypersensitive. In the place of the a & 250 MECHANICAL DENTISTRY. layer or layers of foil in the joint, a drop of gum sandarac var- nish—quite thick—will often be all that is required to accom- plish the same results. Where the end of the root is extensively decayed, the jagged interval in adjustment may be filled with gold or gutta-percha according to the judgment of the operator. The screws should be made of the best watch-steel wire, and in the main shaft do not require to be larger in diameter than a small knitting- or common-sized darning-needle. The screws may be also slightly washed in a nickel bath to suit a whim or fancy, but practically they have no advantage whatever over plain screws, for the obvious reasons of their seclusion and dry- ness when in position. Most of the anterior roots will, for a sufficient distance, permit the use of a drill which is three or four, or even five times the diameter of the screw. A plug of hickory in such cases is firmly set in the hole thus drilled in Fig. 123. Fig. 124. W the root, and the end of the wood neatly finished with the outer surface. The tooth crown, now firmly held in the desired po- sition on the end of the prepared root, will act as a guide in drilling for the screw, the drill passing up through the poste- rior cavity of the crown. Presuming, of course, that the nerve cavity is filled to the screw with gold, a vertical half section of the root and crown with the inserted wood for the attachment of the screw would appear as in Fig. 123. At a appears the wood, and at b the external gold plug. The final attachment is facilitated by having previously run the screw once through the wood before the crown is put on. A tap for the screw is easily made from a broken excavator, or other instrument of like dimensions, by drawing the temper and cutting the same thread as the screw for a suitable distance upon the end. After ROOT CROWNING. 251 the end is slightly rounded, three grooves, equidistant from each other, should be filed rather deeply, lengthwise of the tap, then the whole tempered and drawn back to straw color. The screws themselves will run better by being grooved likewise, but should not be tempered. However, if a tap is necessary, and a regular one is not at hand, from accident or otherwise, the screw, already grooved, needs simply to be tempered to act admirably in a double capacity. " We have spoken principally of the anterior teeth. We will now refer to this method as applied to those teeth, in either arch, that are posterior to the canines. " It will be evident from the principles involved, that bicus- pid and molar crowns can be applied with the same facility, especially whenever their situation in the arch will permit the use of the drill. Bicuspids are treated in the same manner as the anterior teeth, save that in the strong, broad, and frequently bifid roots of second bicuspids, two screws may attach the crown, especially where extra strength will be required from their situation in mastication. " Fig. 124 will illustrate a second upper bicuspid, in part sec- tion with two screws. Upper and lower molars will require two, three, or more screws, as the operator may determine. Many more layers of foil will be required for molar crowns than for others, in order to secure an equal perfection for their joints. Where many crowns may be called for in a case, the carver is indispensable. In cities, and in offices, even, where good car- vers may be had, nearly if not every tooth may be carved by him to suit each place precisely, and little or no fitting will be required. More diversified and desirable results are thus ob- tained. In the country, and places too remote for such advan- tages, the anterior and bicuspid crowns may be furnished in various colors and shapes after the ordinary patterns. Excel- lent crowns of the above description have been furnished us by the enterprise and accommodation of S. S. White from molds made expressly for such. " In the matter of screws we will merely remark that, as no town furnishes a dentist without at the same time furnishing him with a neighbor equally constant, omnipresent, and inde- 252 MECHANICAL DENTISTRY. fatigable,—the jeweller,—the facility of obtaining screws made to a desirable pattern will be abundant and satisfactory. Where it is decided to give the carver an opportunity to dis- play his skill, whether it be upon one crown or a dozen, an im- pression in plaster will be necessary. Preceding this, all the crown-bearing roots should be prepared, dressed, and drilled the same as for setting, but not tapped. Bits of wire of any kind, the diameter of the drill, are now set in each place intended for a screw, and rising to the height of the future crown. These pins should sit in their places easily enough to come away readily with the impression when it is withdrawn. The removal of the impression from about the other teeth may be facilitated by the use of a slight portion of glycerin applied with a small camel's-hair brush about their necks and crowns. Glycerin, though agreeable of itself to most people, may be ren- dered quite so by perfuming it with some generally acceptable odor. The impression being now removed is carefully var- nished and oiled, the pin or pins remaining in situ. From this the true cast is made, the pins now being transferred to this one in turn. By careful manipulation and cutting the pins will part with the old cast or impression with little or no difficulty. The purpose of these pins is to serve the carver for attachment of the ' body ' in its first molding, and give, at the same time, the direction and diameter of the screws in the crown, the heads of which should finally occupy the position of about a sixteenth of an inch from the joint. A plaster bite of the an- tagonizing teeth should also accompany the final cast. If shrinkage in baking of the crown will not permit the passage of the screw freely, a small, soft steel mandril in the lathe, with the use of oil and the flour of emery, will be efficient. " Fig. 125 represents a case where eight crowns have been set by this method. The black dots represent the gold fillings over the screws— two in the second bicuspid and three in each of the two molars. " In conclusion, with regard to the above method of crowning roots, and its application, we may be permitted to offer for consideration a summary of its characteristics:— " 1st. Its simplicity, neatness, and permanency. ROOT CROWNING. 253 " 2d. The impervious and antiseptic character of the union of crown and root. " 3d. The practical application of these crowns to bicuspids and molars, as well as to the anterior teeth, which have been chiefly concerned in this matter hitherto. " 4th. The use of the screw, which is one of the most power- ful adjuncts in mechanics; and this screw of steel, uniting the minimum of size with the maximum of strength. "5th. The application of an entire crown of porcelain, ivory, or gold and porcelain, as set forth. " 6th. The ball-and-socket principle of the screw-head and Fig. 125. its cavity of reception in the crown, permitting of automatic adjustment to the root, whether in its normal position or other- wise. "7th. The facility with which the carver may adapt one or many crowns in either dental arch. " 8th. The final filling and finish of gold or other material in the posterior cavity over the screw, sealing the whole imper- viously, and at the same time permitting of the speedy and safe removal of the crowm, when necessary from its fracture, or from other cause. 254 MECHANICAL DENTISTRY. " 9th. The many objections it refutes with regard to the popular notion of 'pivoting' teeth in general. Among the most prominent of which are not only the offensive odor and other imperfections of the older forms, but the costliness and tediousness of some of the later ones." Among the more recent and approved methods of attaching porcelain-faced crowns of gold or plastic materials, is that devised by Dr. AY. Storer How, of Philadelphia, Pa., the peculiar and distinctive features of which appear in the following de- scriptions and illustrations reproduced from the Dental Cosmos, April, 1883 :— " The difficulties and uncertainties in mounting artificial tooth-crowns on roots, by either old or new methods, led me to a careful study of the problem, and resulted in a nearly simul- taneous devising of several new forms of crowns and appliances for setting them, as well as a perfected method of performing the operation of fixing a peculiar screw-post (Fig. 12(5) in a root, and also a novel process of attaching the crown to the post. At present I will describe simply the four-pin crown (Fig. 127), and the successive steps to be taken in mounting it. " 1. When the root is in proper condition for mounting, meas- ure the depth of the canal by means of the canal-plugger (Fig. 120) and its flexible gauge (Fig. 131), and fill the canal at and a short distance from the apex of the root, keeping the gauge at position to show the full length of . the canal, and also the distance to which it has been filled. " 2. Cut off the root-crown with excising forceps, No. 31, and a round file, down to the gum margin, and, with barrel-bur No. 241, cut the labial part of the root fairly under the gum without wounding it. " 3. Set gauge (Fig. 131) on a Gates drill (Fig. 130) to one- half the gauged depth of the canal, and drill to that depth. " 4. Set the twist drill (Fig. 132) in its chuck (Fig. 135) to project the same length as the Gates drill, and turning the chuck with thumb and finger, drill the root to exactly that depth. " 5. Enlarge the mouth of canal one-sixteenth of an inch deep all around to near the margin of the root, using square-end ROOT CROWNING. fissure-bur No. 59, and then with oval, No. 94, undercut a groove at sides and lingually, as shown in Fig. 128. " 0. If the rubber-dam is to be used for a gold or plastic back- FiG. 126. Fig. 127. Fig. 12S. Fig. 129. Fig. 130. Fig. 131. l/^ Fig. 132. Fig. 133. Fig. Fig. Fig. 134. 135. 136. 256 MECHANICAL DENTISTRY. ing, put it now over the root with Hunter's root clamp, also over the adjacent teeth, and thoroughly dry the canal. " 7. Set the tap (Fig. 133) in its chuck (Fig. 136) a trifle less in length than the drill, oil the ta,p and carefully tap to the gauge depth. " 8. Insert the post in its chuck (Fig. 134) to the exact gauge of the tap, and turn the thumb-screw down hard on the end of the post; then screw the post into the root, release the thumb- screw, unscrew the chuck a half turn, bend the post until the chuck stands in centre line with the adjoining teeth, and un- screw the chuck. Fig. 137. Fig. 139. Fig. 140. Fig. 142. " 9. Slit the rubber back from adjacent teeth, tucking the flaps out of the way, so that occlusion may be tried, and the post excised and ground off until the teeth close clear of the post. " 10. Try the crown on the post, and with an F disk, dry, grind the rib between the neck pins until the crown is labially flush with the root margin, cutting a little at a time until exactly flush. " 11. Take the crown and place the mandrel (Fig. 137) between the pins just as the post is to be, and with the pliers (Fig. 138) bend the pins carefully over the mandrel, cutting off the pins ROOT CROWNING. 257 if too long to be pinched in on the mandrel at the sides, ob- serving that the pin nearest the cutting-edge is first to be bent (Fig. 140), and the opposite pin bent below it on the mandrel, and so with the others (Fig. 141). "12. Slip the crown over the post, try occlusion, and with the post-chuck bend the post until the crown is properly aligned with the teeth; then with a stump corundum wheel No. 3 grind the neck of the crown to a close labial fit with the root, fitting only the portion to be concealed by the gum, leaving narrow gaps at the sides to be filled by the backing between crown and root (Fig. 142). . "13. Grind cutting-edge for relation to the other teeth, being sure that opposing tooth does not strike crown, or post, or pins. " 14. Fix crown on post by pinching the pins into the screw- threads of the post with special pliers. (Fig. 138 or 139.) Fig. 144. Fig. 145. " 15. Finally, pack the backing of gold, or cement, or amalgam, or Wood's metal, or—for temporary backing while treating abscess—gutta-percha, into all the crevices around the post and behind and under the pins, and between the crown and the root; contour and finish thoroughly, so that no ledge or other imperfection can be found. " Figure 143 shows in vertical mid-section an incisor crown mounted; the blackened portions of the backing defining the locking-hold of the backing on the post, the crown-pins, and the root recess. " Figure 144 shows in perspective a cuspid crown ready to be slipped over its post, and also a cuspid crown ready for its post in the bicuspid root, which has its lingual cusp remaining, and Fig. 145 shows the crowns on their posts awaiting the contour- backing. 17 258 MECHANICAL DENTISTRY. " In mounting a crown on the bicuspid root (Fig. 144), the chucks will not usually pass the natural cusp, and hence both the drill and the tap must project the cusp's length in addition to the gauge length. Observe, also, if the space between the tap and the cusp is wider than the thickness of a crown-pin, and if not cut the cusp vertically with a large fissure-bur so that the space shall be wide enough, before setting the post, else the bent pins will not pass between the post and cusp. Grind the rib— see step 10—quite down to the floor of the crown; take steps 11, 12, and 13, and if the occlusion necessitates grinding the crown so as to destroy one pair of pins, invest the crown, and solder the pins at the lap, taking step 15 for completion. " When it is desired to contour the backing of a cuspid crown Fig. 146. Fig. 147. Fig. 148. Fig. 149. to form an inner cusp, or to adapt a cuspid or incisor crown for masticating uses, the pins may be twisted together over the mandrel, and again twisted tightly over the post as in Fig. 146; but in some cases it may be better to bend the neck-pins, as in Fig. 147, instead of twisting them. In all cases the bent pins are to be pinched quite hard over the mandrel and post, so that the serrations of the pliers will roughen the pins to prevent their being pulled through the backing, which should also be condensed around the pins and post. " If the root is not ready for permanent mounting, use a tubular post, or, in the absence of a threaded tube, take the successive steps up to 13; then back temporarily with wax, rubber, or gutta-percha, awaiting the next sitting, when the ROOT CROWNING. 259 crown may be taken off, the post unscrewed, and the remedy applied. Thus the root may be alternately medicated and mounted until ready for the permanent crown. " When the root is much decayed, the bottom of the cone- shaped cavity may be drilled and tapped to the depth of a sixteenth of an inch, and the post, thus anchored, may be fur- ther secured by cement in the grooved walls of the cavity and around the post (Fig. 148). " These crowns afford unusual facility for mounting by any of the well-known methods of inserting the post, after soldering it to the crown. They are also adapted for use in celluloid and rubber work, especially in cases of single teeth. The several long pins, having their ends bent with pliers at a sharp angle Fig. 150. Fig. 151. Fig. 152. Fig. 153. (Fig. 140), may be so arranged as to both strengthen the shank of the plate and hold the crown very firmly in position. " The screw-posts are made of crown metal, an alloy devised for the purpose in order to obtain a stiff post that will permit the cutting of the peculiar and extremely accurate thread formed upon it, and which will not amalgamate or be other- wise affected by any backing material that may be used. Of course, platinum or platinum alloyed with iridium may be em- ployed for posts, but the crown metal is in every way superior. " There are some cases of a class which has hitherto presented difficulties that may now be easily overcome by grinding the post flat on the crown side after it has been set and bent in the 260 MECHANICAL DENTISTRY. root (Fig. 150), so as to be clear of the occluding tooth; and then the crown-pins may be bent over the reduced post, the crown fitted and ground to clear the opposing tooth (Fig. 151), and the backing added. "A similar case, in which the opposing tooth and a proper alignment require an oblique bending of the pins, is seen in Fig. 152, while the reverse arrangement of parts is shown in Fig. 153. The crown is thus seen to be adapted to a wide range of adjustments because its point of contact with the root is at the labial portion of the neck, on which, as on a hinge, the crown may be swung out or in (Fig. 154, dotted lines), over an arc of at least sixty de- grees, at any point of which it may be quickly and firmly fixed. The labio-cervical junction is made just under the gingival margin, and I usually in- terpose a thin layer of cement, amalgam, or gutta- percha, or a narrow ribbon or several large blocks of soft gold; the joint always to be made smooth, and hid from view under the free margins of the gums. " The obviously great advantages of such a plan led to the adoption of a single size for post and appliances, but a second size has been proved to be a necessity, and hence the B size is now designed for superior centrals, and cuspids, while the A size is used for laterals and bicuspids, as also for all the inferior roots anterior to the molars. The handles of the tap-chucks and post-chucks are made of small diameter to insure that too great force shall not be used with the thumb and finger in turning in the tap and the post; and it is enjoined upon the operator to remove the tap when it begins to turn at all hard, and repeat the removal until it has been easily turned down to the gauge depth. The cuttings must then be carefully blown or wiped out, so that the post may be easily turned down to the bottom of the hole without risk of splitting the root, as there is danger of doing with too great force acting on the debris as a wedge—hence this caution to employ only a reasonable amount of force and to do thorough work. The disk for grinding the crown-rib is an essential part of the equipment, and when the ROOT CROWNING. 261 engine is not at hand, may be used in the lathe, by means of lathe-chuck No. 8." The author is indebted to Dr. How for advance proof-sheets of the following article contributed to the February (1886) number of the Dented, Cosmos, entitled "A System for Collar- Crowning and Bridge- Work: "— "The object of this paper is to present as briefly as may be, Fig.- 155. Fig. 156. Fig. 157. and without discrimination as to the new or old features, a system of crowning and adapting gold collars for crowns, or for bridge-work. "To illustrate: Given the sound roots of an inferior molar which it is desired to crown,—previous treatment having brought it into a suitable condition for the operation. Trim and smooth the cervical margins; enlarge the pulp-chamber, 262 MECHANICAL DENTISTRY. undercut its walls, and fix in the root-canals two screw-posts so that they will slightly project from the chamber (see Fig. 155). Secure a measure of the root by a piece of No. 26 binding-wire, twisted, as shown in Fig. 156. Lay the wire-loop thus formed on a block of lead, and with a broad-faced hammer drive it into the surface of the lead so as to secure an accurate impres- sion (see Fig. 157). Place the loop on a suitable molar mandrel (see Fig. 158). Measure with a wire around the mandrel just in front of the loop, in order to obtain the precise inside cir- cumference of the collar required. Make, or select, a collar of the requisite size and proper width for the case; place it on the Fig. 160. mandrel; hold both on the lead block (see Fig. 159), and with light taps of the hammer No. 10, conform the collar to the mandrel until the wire-loop will just fit snugly on the man- drel, close in front of the collar. That edge of the collar should then exactly fit the impression of the loop in the lead; if not, it may be made to fit by the judicious use of the pliers; but, if found too large for the root, put the collar in the proper hole of the contractor (Fig. 160); cover it with a piece of hard sheet-metal, and strike the metal with a hammer for the effect shown in the sectional Fig. 161. By these means a perfect fit of the collar on the root-neck may be quickly obtained. The ROOT CROWNING. 263 collar may be contoured (see Fig. 162) by using the peculiar pliers illustrated by Fig. 163. The same pliers, by turning aside the pivoted plate, will serve to punch projections on the inner surface of the collar, as in Fig. 164, to prevent it from slipping too far on the root (see Fig. 165). A suitable cap may now be soldered on the collar, and the crown may be attached to a bridge, or mounted as usual. Seamless collars are more perfectly adapted, smoother in finish, and need not be invested Fig. 161. Fig. 162. Fig. 163. when the cap is being soldered. A porcelain crown section renders unnecessary any soldering, and is illustrated in Fig. 166. " After the collar has been fitted and adjusted, as has been previouslv described, a porcelain section is placed in the collar, and the proper occlusion obtained by grinding either the cusps or the top edge of the collar with engine corundums. Then all moisture is removed from the root, collar, and section; the collar put over the root, and plastic cement, or thoroughly 264 MECHANICAL DENTISTRY. softened gutta-percha, quickly packed into the collar and around the screw-posts, until the collar is nearly filled, and a little of the plastic material is placed around the pin in the section, which is then pressed into place; preferably by the occluding tooth. The surplus plastic material will exude between the collar and the section, and the joint will be imperceptible if the operation has been skillfully performed. The final finish can be given after the cement has become hard. Fig. 1(57 shows such a completed crown. Fig. 168 illustrates a modified porcelain section, the sloping sides of which admit of oblique adjustments for occlusion without grinding off the cusps of the section. At first thought it might appear as though the various sizes and shapes of the necks of teeth would compel the possession of a very large variety of mandrels to meet the needs of practice; but the fact is, that the several classes of teeth have certain generic forms which admit of such grouping as to reduce the number of mandrels to seven as to shape, while variations in size are provided for by suit- ably tapering the mandrels. " This system simplifies the manipulative process of collar- crowning as designed for either a single tooth, or for the tooth abutments of bridge-work; and, while lessening consumption of valuable time, it also increases greatly the expectation of durability by reason of an assured adaptation of the collar to the root-neck, and a consequent firmness of the crown attach- ment." Banded or Ferruled Crowns.—What is known as Richmond's method of attaching artificial crowns to the roots of teeth is applicable to bicuspids and molars as well as to single-rooted teeth. The latter, or incisors and cuspidati, however, are por- celain-faced, and are constructed and fixed in the following manner:— Prepare the root in all respects as in the case of an ordinary " pivot" tooth. Bevel the sides of the dressed end of the root with chisels or other suitable instruments one-half or three- fourths of a line in depth, forming parallel walls for the recep- tion of a narrow gold band, which is subsequently to be forced over the end of the root. Take then a narrow strip of gold ROOT CROWNING. 265 plate (that made from the gold pieces coined since 1860 being the best adapted to the purpose) about 24 gauge, and three lines or more in width. With round-nosed pliers, bend this strip so as to encircle the end of the root; mark the point of junction and cut off. From this again cut off from one-six- teenth to one-eighth of an inch according to the size of the root, and unite the ends with solder composed of gold coin same as band five parts, and one part of fine brass wire. Y ith files or corundum disks fashion this band so that, while it is of equal width, it will conform to the marginal contour of the dressed end of the root, the edge of the band underlying the gum, presenting, when finished, an antero-posterior convexity and lateral concavity corresponding with the marginal inequal- ities of the alveolar processes. Bevel the outer and upper edge of this band, and force it over the end of the root. Fit a gold or platinum wire pin to the enlarged opening in the root accurately, but not so tightly as to prevent its ready withdrawal on gentle traction, and long enough to project a line or more from the orifice. With the metal pin in place, take an accurate impression of the parts, including the adjoining teeth, and remove carefully, when the metal pin will be found imbedded in the wax impression, or if not, it may be afterwards removed from the root and adjusted in its proper place in the impression. The gold band should also be forced from the root and placed in the impression. The latter should then be filled in with plaster to secure a model of the parts, with the pin and band secured in their proper re- lations. Then cut and fit a cap of thin platinum plate, perfo- rated to pass over the pin and down upon the end of the root, or within a little distance of it, leaving some space underneath for plastic material on final adjustment. This platinum cap should fit into the gold band accurately. Next, select and ad- just a suitable plain plate tooth to the space to be supplied; remove and back it with a thin plate of platinum, and rivet or bend the pins to secure it in place. Then readjust it in its proper place on the model, and secure it by adding fresh por- tions of plaster and sand, building it up over the front face of the tooth and around the model. 266 MECHANICAL DENTISTRY. The several parts are thus secured in their proper relations to each other. When the investient is sufficiently hard, heat up the piece slowly, and with the blowpipe flow in upon the parts exposed to view successive portions of gold solder, com- pounded as before mentioned, until sufficient has been added to form the desired posterior contour of crown. The piece, when properly dressed and polished, is now ready for final and permanent adjustment to the root, previous to which, however, the walls of the root-canal should be rough- ened or grooved somewhat, and the wire pin or dowel barbed or serrated. Before forcing the band, with tooth now attached, over the root, introduce into the enlarged canal of the latter, and around the base of the crown, sufficient oxychloride or oxyphosphate of zinc, German cement, or other allied plastic material, to fill completely all vacuities that may exist around the metal pin and underneath the platinum base plate, securing by this means increased attachment and stability to the substitute. To permit the escape of surplus material a small opening may be made with a drill through the posterior face of the crown near the band, and which may afterwards be closed with gold foil. When in place and firmly fixed, the lower edges of the gold band underneath the gum should be forced in closely upon the root with burnishers. In attaching artificial crowns to the roots of bicuspids and molars by this method, the operation is simplified somewhat by constructing the crown, superficially, exclusively of gold plate. A band, of the quality of gold before mentioned in con- nection with the front teeth, equal in width to the required length of crown, is employed, and is prepared in the same manner as the narrow band. The end of this gold tube or band antagonizing with the teeth of the opposite jaw is then closed with a platinum cap fitting into it, and solder flowed over this until sufficient thickness is provided for purposes of mastication, while cusps are raised by adding and flowing ad- ditional pieces of solder at appropriate points. A small opening having been previously made for the escape of surplus, the hollow crown is filled with some one of the plastic materials ROOT CROWNING. 267 heretofore mentioned, and the crown forced over the root and into proper position. Increased stability and firmness of at- tachment may be secured by fixing serrated gold wires in the roots before placing the crown. The following method of substitution, contributed, at the solici- tation of the author, by Professor M. H. Chappell, of the Indiana Dental College, though similar in some respects to that practiced by Dr. Kichmond, is sufficiently original and distinctive in its main features to warrant its introduction in this connection. Having formed and»fitted a gold band to the root in the man- ner heretofore described, the writer continues: " Fit the crown to the root, and to the ferrule or band; bevel the tooth at the gum edge; dress the inside of the band to a sharp edge, so as to form a lap joint with the tooth; or, if preferred, use diamond disk and cut shoulder in crown to receive the untrimmed edge of band. " The pulp or pivot canal must be drilled in a line with the palatine surface, so that the plate will not have to be forged back under the tooth. The canal is made the usual size and depth for pivot teeth. ' " A backing of the same quality of gold as the band, soldered to a thin plate of platinum, is the best. Punch or drill holes to attach the tooth pins; countersink and rivet solid. Have sufficient plate of backing to form the pivot. Yrith a fine saw or separating file cut in each side at base of tooth one-third way off, and bend in the edges forming a tube for pivot. Solder the rivets and upper part of tube to make firm. " The tooth and ferrule are now ready to be attached. Dry the mouth and root, using napkins and saliva ejector. Force the band over the root, firm and perfect, to the exclusion of moisture. Line the inside of band and end of root with gutta- percha, extending it down the canal. Etch the tube or pivot so that the beards of etching touch the walls of pivot canal. Fill the tube of plate with gutta-percha, and line the etched surface and end of crown. Heat the artificial crown and gutta-percha on water-bath pan, and with warm pliers place the tooth in po- sition, forcing the pivot to its place. YThen cool, burnish the band or ferrule to root and crown. 268 MECHANICAL DENTISTRY. " Have retaining-points in root and tube; build up with gold from root and ferrule, to give the proper contour of the palatine surface of the natural teeth. After polishing the ferrule or band and palatine filling, the case is complete." Dr. H. W. F. Biittner, of New York City, to secure the at- tachment of a porcelain crown to the root, has made available the mechanical device known as a mortise-joint, the root being shaped by trephining to the form of a tenon, a gold band or ferrule forming the mortise. The following is his description of the process:— * " In my method of setting artificial crowns, I claim simplicity of construction, firmness, durability, and arrest of decay of the root (Fig. 169). From the following description of my method it would seem that a failure would be almost impossible. To pro- tect the end of the root from decay, and to obtain a strong hold for an artificial porcelain crown, a gold band, properly applied, must be of the greatest bene- fit. I am aware of the fact that gold bands have been applied, but I am convinced that their adaptation after any of the old methods is defective. What I claim in my method is the pre- paration of the neck of the root by a set of instruments espe- cially constructed for that purpose. These instruments enable the operator to obtain as nearly perfect adaptation between the gold band and the root of the tooth as can possibly be made. With reference to the upper centrals, laterals, and canines, as well as the corresponding lower teeth and bicuspids, there can be nothing more favorable than the application of this method. It is true that this process cannot be applied with the same ad- vantage to the upper bicuspids or any of the molars, but I hope in time, if I am in any way supported by the profession, to solve that problem. I believe I will succeed in constructing a set of instruments which will prepare a root, the pulp of which is alive, and may, if healthy, be readily kept so. But as this set of in- struments is not quite completed, I will abstain from its description, and only allude to the setting of crowns which require the devitalization of the pulp, unless this organ has ROOT CROWNING. 269 previously died. Yxith these instruments a circular shoulder is turned on the neck of the root. " The alteration of the neck of the root, from an irregular cone to a cylindrical form, enables us to adapt a corresponding ring or cap. Such a cap, when fitting accurately around as well as upon the end of the root prepared by these instruments, forms an air-tight joint, and consequently protects it from decay, at the same time giving the porcelain crown, when at- tached, a firmness which heretofore has never been obtained. The set of instruments by which the neck of the root is pre- pared consists of drills, reamers, and trephines. The drills (Fig. 170) are used to enlarge the root-canal for the guidance Fig. Fig. Fig. Fig. 170. 171. 172. 173. Fig. 174. of the reamer or facing instrument and trephine. The reamers (Fig. 171) cut the surface of the root down as far as necessary. They produce a perfectly level surface and have a centre-pin, which corresponds with the hole made by the drill in the centre of the root, and acts as a guide. The trephine (Fig. 172) has also a centre-pin, and is used to make the root cylindrical below the free margin of the gum. A set of these instruments in- cludes different sizes of drills, with reamers and trephines corresponding in size adapted to various diameters of roots. " The ferrules or caps (Fig. 173) to fit roots which have been prepared by the above instruments are of gold, made by steel dies. They correspond exactly with the trephine in diameter 270 MECHANICAL DENTISTRY. and depth, with allowance for sufficient expansion of the gold when forced on to the shoulder of the root, whereby a most perfect joint between cap and root is obtained. They have a stout central pivot which fits the hole in the root and gives in- creased strength and firmness. " The pulp-canal is enlarged with one of the drills selected with reference to the size of the root. A reamer corresponding in size is used with the dental engine to cut the root down to a perfect level. The trephine is applied in the same manner to give a cylindrical form to it, thus completing the shoulder (Fig. 174). " A steel wire corresponding in diameter with the drill which has been employed is now introduced into the root, projecting out about half an inch. It serves to indicate the exact direc- tion of the root-canal. An impression-cup is selected with an opening opposite the missing tooth to take an impression of the root and adjoining parts. The object of the opening is to give free transmission to the wire in the root-canal. The wire pro- truding through the cup and impression-material is drawn out carefully before the removal of the impression-cup, which is then removed and the wire placed in its proper position in the impression. A set of brass root-models (Fig. 175) corresponding in size with the instruments accompany them; one of these) bearing the same number as the instrument with which the root has been prepared, is now placed on the wire in the im- pression, and serves to represent the prepared end of the root on the model. The impression is now ready to be filled with -»,. blaster. After the cast is obtained, we find ' the root-model imbedded in the plaster and the wire in its centre-hole. The wire is now removed and the plaster cut from around the root-model to the depth of the gold cap, which is ready to be placed upon it. A plain porce- lain tooth (Fig. 176), as used in plate-work, is ground hollow on the inner surface to cover the outer front wall of the cap, thus hiding the gold. Thin platinum backing is now adapted to the tooth, which is then ready to be placed in position on the model over the gold cap, and fastened thereon with hard wax. ROOT CROWNING. 271 The united parts are removed carefully from the model, invested in sand and plaster and soldered. After polishing, the cap is ready to be forced upon the root by placing a piece of wrood on the cutting-edge of the tooth and driving it home with a mallet." The following process of forming and attaching a porcelain- faced crown, copied from the October (1883) number of the Odontographic Journal, is the device of Dr. A. E. Matteson, of Chicago, 111. The method of constructing a shell in conformity with the general configuration of the natural crown is unique and original, while the facility with which it can be so shaped, the accuracy and security of its adjustment to the root, and the ready manner in which the porcelain face may be replaced in case of accident, are points of excellence that entitle the method to rank among the higher forms of substitution. The several appliances used are exhibited in Fig. 177. Concerning the process, the inventor says:— "The gold-and-platinum plate gives the greatest strength without an excess of material, permitting the use of a higher grade of solder than could be employed were gold alone used, without the consequent danger of melting the shell; and being of uniform thickness, its thorough adaptation to the end of the root is rendered a matter of comparative ease and certainty. It also permits the use of amalgam, the strongest cement we have, for anchoring the crown without danger of injury to the gold. I will say, however, to those who are opposed to the use of amalgam, that gutta-percha, or any of the cements, can be sub- stituted, and with as good results as in any other position in the mouth. " The opening in the front of the shell gives an opportunity to see that the filling is properly introduced and thoroughly con- densed, and is not guess work. " The porcelain front is not dependent upon a few small pins for support, but upon the dovetailed slot, further supported by the edges of the shell which entirely surround it; and in case of fracture, a new front can be easily inserted without removing the shell. " Of no small importance is the ease with which this crown 272 MECHANICAL DENTISTRY. can be made. Even in the hands of those unaccustomed to metal work, good results may be obtained. " The forceps, with a set of eleven dies and counter-dies, are all that are required in addition to the instruments usually in possession of a dentist in practice. " The root upon which the crown is to be mounted should be placed in a healthy condition, with the nerve-canal filled at the apex, the end ground off below the free margin of the gum Fig. 177. in front, and within an eighth of an inch of the gum on the inner or lingual surface, the end of the root countersunk, and the nerve-canal enlarged sufficiently to receive a platinum wire —No. 18 or 20, standard plate gauge—with a screw-thread cut thereon. This should fit tightly enough to take firm hold. Further enlarge one-half the length of the nerve-canal with a cone-shaped bur, with its base toward the apex, as represented in the accompanying cut, numeral 1. ROOT CROWNING. Z / o " Previous to grinding the end of the root below the gum in front, with fine binding wire, take a measurement of the cir- cumference of the root, at the margin of the gum. Cut across at intersection and carefully remove the wire ring thus formed, without changing its shape. Take an impression of its form, by placing it between a sheet of writing paper and a smooth surface, and by rubbing the end of a finger thereon, the out- line will appear. This is the outline of the end of the root; from this cut a pattern. " Select a die similar in shape to the tooth you wish to repro- duce. Make a pattern of the shell, by pressing between the dies a piece of thin copper or pattern tin, leaving an opening in front, with a band extending around in front, as represented in Fig. 3, the cut being on a line with the edge on one side. Re- move this pattern and press into as plain a surface as possible. " Cut the gold-and-platinum plate to pattern, making it wider or narrower, as the wire measurement of the end of the root compared with the pattern indicates. Anneal and place the plate in the same position between the dies as that previously occupied by the pattern; and press into form, remove, bring the edges together without lapping, and solder with pure gold. The shell may be made longer or shorter, wider or narrower, than the die upon which it was made, as the case demands. " To fit the shell to the root, trim the root end of the shell until it occupies its proper position and the articulation is cor- rect, which is determined by the patient closing the teeth. The corners at the cutting edge and sides should be cut, and the edges brought together without lapping, and also soldered with pure gold. " Now, from platinum plate No. 30, cut the ring, Fig. 4, to the paper pattern. This forms the shoulder within the shell. Place the shell in position on the root (the teeth closed), insert the ring, which should rest upon the end of the root midway the width of the band in front, and should fit the shell tight enough that both can be removed without changing their rela- tive positions. Remove from the root, and with a fine camel's- hair brush apply borax, finely ground in water. At the junc- tion of the two pieces, place a small piece of 20 c. solder on the 18 274 MECHANICAL DENTISTRY. inner surface; i. e,, toward the cutting edge of the shell, to pre- vent an excess of solder flowing between the shoulder and the end of the root upon wThich it will rest. Flow the solder, which should merely tack the ring in place at the front. Try upon the root to make sure of its being correct; remove, and com- plete the soldering. The shell may be strengthened by flowing inside a lower grade of solder than previously used, at such places as desired. " Select a plain rubber tooth and fit to the opening in the shell (which may be removed for the purpose), and with corun- dum wheel and disk grind a dovetailed slot in the back (see Fig. 5) running lengthwise, and sufficiently deep to permit the platinum screw to extend two-thirds the length of the crown without interference. " To anchor the crown to the root, place the shell in posi- tion, apply the rubber-dam over it and the adjoining teeth, turning the edges well under the gum. Remove the shell (the dam will remain in position), dry the nerve-canal, insert the wire screw, cut it off the required length, and with amalgam mixed hard, fill around the screw in the root, and covering the end, again replace the shell on the root (the end of the screw should be bent against the inner wall of the shell when the teeth are closed, so as to fall into the dovetailed slot in the porcelain front, when that is inserted). Continue the amalgam filling, through the opening in the front of the shell, around the screw, and over the shoulder, as represented in Fig. 1; and with oxyphosphate cement, complete by filling around the wire and in the slot of the front, which is then inserted and pressed into position by the thumb and finger, the excess escaping at the edges. Burnish the edges of the shell around the neck of the root and porcelain front. Instruct the patient not to disturb it for from four to six hours. " In conclusion, I will offer some suggestions. The dies are fitted to the forceps with the cutting edges of the teeth turned toward the handle. Be careful that the dies and counter-dies do not get mixed. Preserve the pattern of each die with which it should be left, as it will save valuable time. Apply the flux (borax) only where you wish the solder to flow, and cut the ROOT CROWNING. 275 solder in small pieces, using only sufficient to accomplish its purpose. " Amalgam may be made to set more quickly by incorpo- rating gold with the mercury, say five per cent. Foil scraps are excellent. " In case of fracture of the porcelain front, remove the pieces and fit in another, without removing the shell from the root. Cement in as before. " The cut represents the forceps, one-half size. They are one-half nickel-plated. The dies are full size, nickel-plated, and are interchangeable in the screw sockets. " The gold-and-platina plate is made by sweating pure gold upon a plate of equal thickness of platinum, and rolling to the desired thickness (No. 32, plate gauge), and can be obtained at the dental depots." Prof. Y^ilbur F. Litch has devised a modification of the ordinary band or ferrule, in which this means of support is applied in most cases only to the posterior and lateral walls of the root, extending under the free margins of the gum, and to a point on either side midway between the palato-labial aspects of the root. The following description of the method of constructing this partially-banded appliance, which is desig- nated as the " Collar Crown," is taken from the Dental Cosmos, September, 1883:— " In this paper will be explained and illustrated a method for the mounting of artificial crowns, which the writer has taught and practiced during the past few years, and which he has found to quite perfectly meet the true mechanical requirements of that class of substitutive operations. The method is more particularly applicable to the incisors and canines of the upper jaw. "A fairly typical case would be a well-developed upper in- cisor tooth, in normal relation with its fellows, in which, in consequence of the ravages of caries or other misadventure, only a small portion of the crown remains. Such a case is rep- resented in Fig. 178. " The earliest form of what is, absurdly enough, known to the profession as 'pivoting' was that in which a natural 276 MECHANICAL DENTISTRY. crown was attached to the root by means of a wooden pin or dowel; subsequently a porcelain crown, of the same size and shape as the natural one, was employed, the wooden pin being still retained. " The use of this form of crown made the removal of every portion of the natural tooth up to the gum margin absolutely necessary, thus sacrificing often a very considerable amount of tooth substance, and to that extent still further weakening the organ; as, other things being equal, the greater the amount of material in the tooth or in the root, the greater will be its resisting power to the forces to which it may be subjected. Al- though, as will presently be shown, with the introduction of plate teeth, metallic backing, and pin for artificial crowns, such extreme sacrifice of tooth substance was no longer required, in this respect the old method is still very generally followed. " The process to be described reduces this destruction of tissue to the minimum. Instead of cutting the palatine wall of the tooth down to the gum margin, the greater portion of it is carefully conserved, its presence, while not indispensable to a successful result, being in the highest degree desirable. How much of this portion of the tooth can be retained will depend upon the nature of the occlusion. " In Fig. 178, the dotted line from C to D represents the point to which the tooth is cut away in the older methods of 'pivoting;' the dotted line from A to B, the line of abscission practiced by the writer. "As will be seen by reference to Fig. 179, the face of the tooth thus prepared presents a gradual slope from the palatal surface „ „ to the labio-cervical margin. Fig. 178. Fig. 179. . , ,, , ^ . . 5 At the latter margin the root should be cut dowm with suit- able burs, etc., to a point a lit- tle beneath the edge of the gum, in order that the neck of the porcelain tooth in front may pass up under the gum A'' margin and the joint between root and tooth be concealed. At this point tooth-substance may C----*^_-*-----D ROOT CROWNING. 277 be sacrificed, as it does not materially diminish the strength of the root. " The several parts employed in the making of the artificial crown are a plain-plate porcelain tooth, a platinum backing, and a base-plate, collar, and retaining-pin of the same metal. For a solder and covering, either coin-gold or twenty-carat gold, alloyed with copper or silver only, should be employed. " In shaping the pulp-canal for the reception of the retaining- pin, care should be taken not to weaken the root by an unneces- sary enlargement of the calibre of the canal. The platinum pin need not be more than No. 16, Stubs' gauge, in thickness at its point of greatest diameter, near the free surface of the root, where all the strain, if any, falls; from this point it should be made a general taper corresponding to the natural shape of the space it is to occupy. Half an inch in length is ample; even less will serve. The base-plate and collar are made of very thin platinum, about No. 32, Stubs' gauge. The platinum back- ing may be made thin or thick indifferently. " The platinum pin being shaped .and adjusted in the root, care being taken to leave an excess in length at the free end for convenience in subsequent manipulations, the next step in the process is the making of the base-plate and its attachment to the pin. A strip of thin platinum of suitable size is pressed upon the face of the root, with broad-pointed, serrated instru- ments, until it is in close adaptation to the surface at every point. This base-plate is allowed to project beyond and overhang the palatine portion of the root, but should not come quite to the labial edge. "Adaptation being secured, an opening is made in the base- plate where it covers the pulp-canal, through which opening the platinum pin may be pressed up into position in the root. Pin and base-plate are then removed from the mouth, dried, and cemented with a brittle resinous cement, and then, while the cement is still plastic and yielding from heat, placed again in position in and upon the tooth and perfect adaptation se- cured. Then, while still in position in the mouth, throw upon the cement a stream of very cold water, so that it may be made brittle and incapable of bending. Then remove from the 278 MECHANICAL DENTISTRY. mouth and invest in a mixture of equal parts of plaster and pulverized marble or pumice-stone, with enough water to make a thick paste. After the investment has set, solder the platinum pin and the base-plate together. " To make the collar, a somewhat crescent-shaped piece of thin platinum of suitable size is prepared and pressed into shape upon the palatine and palato-approximal face of the tooth; little slits may be cut in the collar with a delicate pair of scissors, to make easier this adaptation. Care should be taken not to push the collar up under the gum at any point, provided the palatine wall of the tooth which had been allowed to remain standing is at all ample in height, say one-tenth of an inch; if less than this, the collar may pass under the gum for a short distance, as will be shown subsequently. In the average case this collar will not quite one-half encircle the tooth. " Fig. 180 shows the collar curved to the outline of the gum margin, and shaped to the contour of the palato-approximal wall of the tooth. At G are the Fig. 180. Fig. 181. . slits cut in the platinum to al- low overlapping in shaping to %£—- i :" 1 contour. " In order to strengthen the collar and facilitate its attach- ment to the base-plate, cut a series of slits in that portion of the base-plate which has been made to project beyond the palatine wall of the tooth, and the base-plate, with its now attached pin, being placed with the collar in position in and upon the tooth, the little strips of platinum into which the overhanging edge of the base-plate has been cut are pressed, one after the other, down upon the collar and carefully molded to its surface, so that the collar will no longer consist of a single thickness of very thin platinum, but will be reinforced by these additional thicknesses of base- plate thus pressed upon it. " Fig. 181 shows this quite perfectly. H is the free end of the retaining-pin which is to be cut off when the porcelain tooth is ROOT CROWNING. 279 mounted. I is the base-plate, with its overhanging palatine margin cut into strips, J, which are being pressed down upon the collar, F, by the broad-surfaced and serrated instrument K. This being accomplished, remove the several pieces from the mouth, carefully cement the collar in its proper position relative to the base-plate, which will now form a sort of matrix for it, again place in the mouth, readjust, harden the cement, remove from the mouth, invest as before, and solder the collar and base- plate together, using a considerable excess of solder for covering, so that the collar may be still further strengthened and its sur- face be made uniform. " In cementing the collar to the base-plate one precaution is imperative, namely, not to allow a film of cement to get between the collar and the tooth. If this is done and the investment poured in upon this film of cement, the latter will immediately burn out as soon as heat is applied, leaving a space between the collar and the investment into which the gold solder will flow, and thus interfere with that perfect adaptation of the appliance to the tooth which is necessary to a successful result. " The mounting of the tooth next demands attention. As already stated, a plain-plate porcelain tooth is used. This must have what are technically known as cross-pins, that is, pins placed at right angles with the long axis of the tooth. They must also be placed well up toward the cutting-edge. If they are too near the neck, they will inevitably be cut out in fitting the tooth to the sharp slope of the base-plate on which it must be mounted. ■ " Fig. 182 shows the form of tooth and indicates Fig. 182. the slope given it in fitting. The fitting process does not differ from that ordinarily employed with porce- lain teeth; an impression may be taken and the work done on a cast, or the tooth may be fitted to the mouth. In either case, it is in the mouth that the finer and final adjustments as to height, contour, alignment, etc., must be perfected. " This being done, and the tooth backed, tooth and base-plate are cemented together, restored to the mouth, finally adjusted, 280 MECHANICAL DENTISTRY. removed, and soldered as before; as much gold being flowed into the acute angle between the backing and the base-plate as occlusion will permit. " This artificial crown being properly finished and cemented into position in and upon the tooth makes what the writer, from several years' experience in its use, in a large number of cases, has found to be an appliance which will remain for an indefi- nite period without the slightest deviation from position and alignment, and which in many respects is almost as strong as the natural tooth, because its point of greatest resistance to pressure is placed where nature anchors her enamel walls, namely, upon the outside and not upon the inside of the walls of dentine; so that in the act of occlusion the force applied by the lower incisors, as they come up in position inside the upper incisors, falls upon the whole thickness of the root through the collar, and not upon less than half its thick- ness through a centrally anchored pin,—a pin, too, prolonged into a lever of enormous power by its attachment to the porcelain tooth. " In this respect there is a manifest weakness in all methods of mounting artificial crowns which depend for their stability solely upon the central pin. Ultimate failure, through splitting of the root, is the frequent result, and the larger and stronger and more deeply anchored the pin, the more certain this result, because a large pin necessitates a large opening for its recep- tion, and a corresponding weakening of the root, upon which the strain must ultimately fall; the lever is strengthened and the point of resistance weakened. " The only safety for the usual form of ' pivot tooth' is, either that the occlusion shall be slight, the root very strong, or the 'pivot' very flexible or elastic. This elasticity of the old hickory ' pivot' was one of its chief excellences; roots were much less likely to split than with a rigid, unyielding, metallic pin. In canines or incisors, however, metallic pins, unless enormously large, or thickly packed around with amalgam, will very often bend outward, thus allowing a slight displacement forward of the artificial crown, and to that extent relieving the root from strain. ROOT CROWNING. 281 " Fig. 183 shows the artificial crown. L is the porcelain tooth, mounted and in occlusion. H is the pin ^ L r IG. 183. attached to I, the base-plate. M is the backing and solder. N is the lower incisor, and F, the collar. It is clearly evident that here the force of occlusion falls upon the palatine wall of the natural tooth at 0 through the collar F, and not upon the pin at the point of its attachment to the base-plate H, and through the pin upon the M-^>|f^ h thin outer shell of the root. " In cases frequently met with, where the entire crown of the tooth has been removed, the collar, as before described, can be adapted to the palatine face of the root, provided the latter be not decayed away up to the alveolar margin. Usually, how- ever, there is a considerable space between the free edge of the root and the alveolus, and here, running up to the alveolus, the collar must be placed. " The dotted line E, in Fig. 179, indicates a collar so placed. All the steps in the process are essentially the same as before described. Adapting the collar to the surface of the root beneath the gum is somewhat painful, but not excessively so, and in the wearing, the irritation caused by its presence is very slight and transient in character, assuming, of course, that care has been taken to leave upon it a smooth, thin, and well-polished edge. " The objection may be urged that this form of crown resists pressure only in one direction, from within outward, and does not provide for lateral pressure or pressure from the front. As a rule, the latter can occur, with any force, only as the result of accident, while if the crowned tooth is in normal relation with its fellows, and the artificial crown be closely fitted in between them, the}7- will fully sustain lateral force. " Where such lateral support is wanting, through isolation of the tooth, the collar must be extended into a ring or ferrule completely encircling and grasping the root, and thus affording support on all sides. The ring, however, is more troublesome to make and more painful to apply, and generally shows a line 282 MECHANICAL DENTISTRY. of gold in front. In the average case the simple collar gives all requisite strength. " In mounting crowns upon bicuspid and molar roots, how- ever, the ferrule principle is often essential to stability; espe- cially is this true of lower bicuspids and molars; as here the forces applied in mastication are as erratic in direction as they are powerful in character, and the root must be guarded at every point against their violence. " In fixing in position the artificial crowns just described, the writer prefers to use a gutta-percha cement very adhesive in character. A preparation sold under the name of ' Prepared Gutta-Percha,' by the S. S. White Dental Manufacturing Co., possesses this property in a high degree, and does not strip from the pin when the crown is forced into position, as would a less adhesive quality. " The apical foramen is closed, the pulp-canal grooved and thoroughly dried, the central pin is barbed, and the pin and inside of the collar and under surface of the base-plate are thickly coated with the gutta-percha; then heat the entire appliance to a temperature sufficient to thoroughly soften the gutta-percha, and firmly press it up into position; the excess of gutta-percha will ooze out at all free margins, and may be subsequently removed with suitable instruments. " This cement will hold firmly in a great majority of cases, but when, as in a small lateral incisor, the retaining-pin is necessarily small and short, and the collar not as ample as could be desired, an oxychloride or oxyphosphate cement, mixed thin, will be found to give greater stability. Ymen these cements are used, however, it will be found very difficult to detach the artificial crown from the root, should it for any reason become necessary to do so; whereas, a little heat will quickly soften a gutta-percha packing and permit the entire appliance to be withdrawn without difficulty." Drs. H. K. Leech, of Philadelphia, and A. 0. Hunt, of Iowa City, have each devised a method of crowning in which a hol- low cylinder or tube is employed as a means of retention, and, in the case of Dr. Hunt's method, to afford access to the terminal point of the root for subsequent treatment, if necessary. ROOT CROWNING. 283 Dr. Leech's mode of procedure is thus briefly described by Dr. Dexter, the general form and "attachment of the cylinder being shown in Fig. 184. " The root is drilled out to a depth of about three-eighths of an inch to a diameter of about No. 16, standard (American) wire-gauge, the bottom of the hole being flared or enlarged, and the canal above filled with gutta-percha. A gold tube is made to fit the hole accurately and project sufficiently for convenience of handling, and is sol- dered through a hole in a gold base a struck to the root, projecting through il the plate some distance. A plate tooth [ J is fitted to the root and plate and sol- I 'l dered to the latter, gold being flowed f~m onto the plate and backing and around j . ;|1 the projecting tube to form the palatal contour, and the tube cut off flush with the latter. YTe now have a plate tooth, gold backed, with a tube pivot, the orifice of which opens on the palatal aspect of our tooth. The root-end of the tube is now slit perpendicularly in three or four places, for about two-thirds of its length, a thin sheet of warmed gutta- percha is placed on the base of the crown around the tube, and the whole is pushed securely to place. Now pack gold or tin into the tube, condensing the bottom portions so that the slit end will spread and tightly fill the flared end of the hole in the root, and the operation is complete. " This way of fastening a pivot tooth to a root is, so far as I can learn, as novel as it is ingenious; and, if tin be used to fill the tube, so that the tooth may be easily removed in case of trouble, it seems an excellent addition to our list of pivot teeth." The following is Dr. Hunt's description of his method of procedure:— " AVhon roots are crowded, the surrounding parts are subject to a class of diseases that are difficult to treat unless the pulp- canal can be utilized, through which to pass the various thera- peutic agents to be employed. 284 MECHANICAL DENTISTRY. " By the usual method of attaching a crown, it is necessary to remove it whenever treatment is to be resorted to. Such removal means destruction to the crown; as one well adjusted will, in nearly all cases, be so badly mutilated in the operation that it is much easier to make a new one than to restore an old. "Again, most of the methods are adapted to roots that are firm, and after being cut off to the line of the gums, retain all their normal strength and form. It is often necessary to operate with roots whose buccal, lingual or lateral walls are disintegrated nearly or quite to the alveolar process. " The interior of the root may be coned out deeply, exposing frail and ragged edges, with the gum tissues overlying these edges. " The method I shall attempt to describe is one suited to these latter cases, i. e., roots with frail and ragged edges, with the gum tissues overlying and filling the crown end. The following method will overcome most, if not all, of the difficulties in the way of success, and allow the setting of a crown that is dura- ble and useful. To get good access to the root, first pack it with soft gutta-percha pellets, pressing the material out over the edges and building on until the gum is displaced, so that when the gutta-percha is removed a large and free opening is had through the gum, and the edges of the root are fully ex- posed. This packing should remain two or three days. With a thin platinum ribbon (33 gauge) form a tube, place it over the end of the root and bind with fine wire, twisted until the plati- num conforms to the shape of the root. " If the edges are too frail, fill with amalgam in the following manner:— " First roughen the inner side of the root or cut ledges, if admissible, with an engine bur. Select a broach that will enter the apical foramen. Leave this in the canal while inserting the amalgam. Restore the contour if lacking at the same time, and withdraw the broach carefully. " The channel thus formed will be a guide in drilling. Wait a day or two for the amalgam to harden; now the end of the root will present a firm face and shoulder, nearly as good as though the walls had never been destroyed. ROOT CROWNING. 285 " With tube over root in place, prepare enough plaster (plas- ter two parts, sand or asbestos one part), and take an impression of this and adjacent teeth, seeing that the plaster fills the tube down to the root. " Yrhen the impression is removed with the band, dry thoroughly. Pour into it Babbitt metal (Grade C) or Watts or Reese metal. " Break away the plaster and remove the platinum tube, trim away in the metal that portion that corresponds to the gum tissue, leaving a correct model of the end of the root over which to place the permanent band of gold. Fit this tightly to the model, turning a flange over the labial edge, as a rest for the porcelain face. Now prepare the following: Hollow platinum wire (No. 60), a twist drill a trifle smaller than the wire with cutting end cone shaped, so that it leaves the bottom of the drill-hole in that form. " Hard wax composed as follows: Gutta-percha one part, pure beeswax two parts, and sufficient resin to form a mass that will be hard at the temperature of the body. Platinum-rolled foil (say No. 45 gauge, to be used as backing for the crown). Put the gold band in place over the root in the mouth, so that the flange is below the gum line. " Follow the pulp-canal with the drill, securing as deep a socket as may be. " Select a suitable plain plate tooth (pins cross-wise pre- ferred), grind to fit, resting the cervical end on the flange of the band. " Lay a piece of the platinum foil on a soft wood surface and press the tooth-pins through it. Burnish the foil down to the tooth and over the approximal, cutting the cervical edges so that at the latter point the foil will be between the tooth and the flange. Adjust the tooth so prepared to its place, driving the platinum tube or wire into the drill-hole, allowing it to extend to the cutting edge of the tooth. With a hot instrument (flat burnisher), melt hard wax about the tube, inside the band and on the backing of the tooth. "Arrange everything now as you would have it when fin- ished. Y ith plaster and sand, or asbe%stos, the same as before, 286 MECHANICAL DENTISTRY. take an impression. Should the tooth and band not draw out with it, they can be removed and put in place in the impression. " Fill all with a mixture of plaster and sand. Remove the cup and trim down on the lingual side, exposing and removing all the wax. Bend the tooth-pins up close to the tube, fill the tube with a piece of broom straw dipped in wet plaster. " Flow solder around these and down over the thin platinum backing until the whole is united to the band at the flange, and a good body of it on the backing. Fit a shell of gold the same grade as the band to the lingual side, resting on the band and fitting the backing closely at the approximal edges and around the tube, which should extend outside of the shell. Solder this in place and finish with files, etc., to a contour corresponding to the tooth being mounted. " Whatever of the tube projects, file off as surplus material. " Place the crown when finished in place, perfect the articu- lation. Remove and attach with cement (Caulk's Diamond preferred). When mixed to the consistency of cream it gives ample time for the work, and sets hard and firm. Remove the piece of broom corn and plaster from the tube; free access can thus be obtained through this channel for treatment now or at any future time. " Fill the tube nearly to the end with cement, closing up with a gold filling. " The advantage of this method will be readily seen. It can be used on any tooth, in any part of the mouth. " In bicuspids with two roots, two tubes may be used ; and the shell for the lingual side, formed over a piece of dry hickory or other hard wood or swaged over metal dies. In molars a tube may also be used for each root. "Another advantage is in having a hollow pin or wire, nearly the combined length of root and crown, firmly imbedded in cement, giving great strength with lightness. Another, the crown is easy of construction, requiring only those instruments usually found in any well-appointed dental office. Still another, it is durable; and the manipulation is positive and adapted to any shape of root. ROOT CROWNING. 287 " In one case where this method was employed, the root was but f of an inch in length (a superior second bicuspid) and quite loose, accompanied with ulceration; so frail that any method of band crowming would have been doubtful. " By this method and with good results in treatment after seventeen months of usage, the root is firm, the crown unim- paired, and all doing the service of a good tooth." Dr. Dexter, in the course of some timely and well-considered remarks on crown- and bridge-work, remarks:— " Yre all now know perfectly well the injurious effects to be ap- prehended from direct contact of metal and dentine in filling teeth. So general is this knowledge becoming that it is rapidly changing practice in this branch. Non-conducting linings are now in common use, and my belief is that their employment will greatly increase. The non-conducting plastics, as we all know, want only durability to become the most valuable of filling materials. Gold, the long-time king of plugs, must now be prevented from doing damage by varnishes in the cavity, by linings of gutta-percha or the zinc plastics, or by encircling him with a zone or belt of mummified protoplasm in the body of the dentine, through use of creasote, alcohol, et id omne genus. For the late discoveries in dental histology, in showing us that a live tooth is not only alive in the pulp but alive all through its substance, have shown us, also, that we must now avoid irritating the living matter in the dentine, as we formerly did that in the pulp itself. To this end we line cavi- ties, varnish cavities, and coagulate the albumen in the tubuli abutting upon cavities. " Now, why does not all this apply as well to the root in pivoting as to the crown infilling? In the root we have a body much more highly organized than the crown; or, at least, the living matter, so abundant in the cementum and pericementum, is much nearer the metal tube, or screw, or filling, than it is to the filling in the crown, and it may be supposed to receive more directly and more acutely the shocks of thermal change. True, the very excess of vitality in these parts gives them greater powers of resistance to attacks from without. But ' dropping water wears away the stone,' and their vitality must, 288 MECHANICAL DENTISTRY. it seems to me, suffer defeat in time, with the result of perice- mentitis, acute or chronic, and other ills. " The ferruled artificial crowns seem to be very open to this objection, particularly when conjoined with screws or pins passing directly into the dentine, and still more particularly when the ferrules, or pins, or both, are in direct metallic con- nection with the broad surface of a gold backing, or a cap or whole crown of metal. Added to this mischief of conduction, in these crowns, is to be apprehended the direct irritation of the ferrule edge upon the gum tissue, or, if deep enough, upon the pericementum......... " On account of the dangers which, to me, seem to lie in the effects of thermal changes upon root-tissues, I must record my- self as opposed, on principle, to all methods of artificial crown- ing in which metallic connection is continuous from crown to root substance. Of course, temperament and organization have much to do with the duration or action of any operation, and I do not wish to be understood as stating that no such operations can be permanently successful. On the contrary, many such do succeed. But I like to be safe, or as nearly so as possible, in my oral ventures, and I interpose non-conductors as carefully in placing crowns as I do in placing fillings." The following method of crown replacement, which the author has practiced to some extent within the past year or two, is in entire accordance with the views expressed above; since, while it embraces the principle of attachment made available in the use of the " pivot" and ferrule, it obviates wholly any contact whatever of metallic substances with the root-structure, within or without. In the use of rubber in the manner to be described, the property which renders it most objectionable when applied to the mucous surfaces is, in these cases, its chief merit, namely, its comparative non-conductibility. The process we are considering can be most conveniently applied to crowning the front or single-rooted teeth, though with proper adjustment of retaining-pins, and the adoption of an oftentimes practicable system of undercutting into pulp- chambers and canals, it may be successfully applied to bicus- pids and molars. ROOT CROWNING. 280 The following descriptions apply to crowning the roots of teeth anterior to the bicuspids. The multiple-rooted teeth would require short, headed pins vulcanized into the body of the rubber crown, the attachment being secured by imbedding these, when setting the crown, in some hard-setting plastic material occupying the countersunk spaces before referred to. 1'orceinin-faced Rubber Crown witli Band Extension.—Prepare the root in the usual manner for banding, dressing it down posteriorly and laterally to within one-half or three-fourths of a line of the gum, and anteriorly just under the free margin. Enlarge the pulp-canal with a drill the size of the central pin selected for the case, allowing, however, for its ready withdrawal from the root. The pin should be made of either platinum, iridio-platinum, or pure gold alloyed with platinum. Take next a very thin strip of platinum or copper plate; bend it around the neck of the root, passing it as far up under the free margin of the gum as possible without wounding the soft tissues; burnish closely to the walls of the root; secure accurate coaptation of the ends, and bind it securely with silver suture wire. The edges of the tube passing under the gum should be conformed as nearty as possible to the alveolar inequalities of contour, while the lower edges should extend but a trifle below the dressed end of the root. Y^ith this temporary tube in place, introduce the central pin into root- canal, select a suitable impression cup, take a plaster impression of the adjoining teeth and interdental space, and remove care- fully—entire, if possible—by sections, if necessary. The pin will come away with the impression, while the tube will remain on the root. The latter must then be removed and placed in its proper position in the impression. The plaster impression is now varnished, oiled, and filled in with hard-setting plaster for the model; the latter representing, when detached from the impression, the exact form and relation of the adjoining teeth, the interdental space, the articulating face of the root, the opening into the root-canal when the pin is drawn, and, on removal of the tube, the exact dimensions and contour of the cervical portions of the root as far up as it is practicable to extend the rubber band. Before removing the 19 290 MECHANICAL DENTISTRY. tube, the groove in which it lies imbedded should be widened to furnish a suitable matrix for the rubber band. This may be readily done by scraping away the plaster all around the plati- num tube with a very narrow, chisel-shaped instrument until the lower edge of the tube is reached at all points, or a beveled groove may be formed all round with a cutting instrument. By untwisting the binding wire, the tube may be easily re- moved, by spreading, without defacing the modeled end of the root. Before removing the plaster from around the tube, how- ever, draw the central pin from the model. Yre have now the portion of the root to be embraced clearly and accurately out- lined on the model, with a proper alignment of the central opening into the root-canal. A suitable plain rubber tooth having been previously selected for the case, articulate it accurately, by grinding, with that por- tion of the model representing the gum in front, and which should be previously pared away slightly and uniformty along the line of contact, while at the same time care should be taken that the tooth of replacement should occupy its proper relation to the adjoining natural teeth. The proper occlusion of the substituted crown can be readily determined by an articulating model obtained from a " bite " at the first sitting, a necessary first step that should always be taken in these cases. The porcelain face, being properly adjusted to the space, may be held in position temporarily by tacking it with a strip of wax in front while the central pin is being replaced in the model and properly aligned with the porcelain face. Before returning the platinum pin to the hole it previously occupied, bend it so that, when inserted, it will take a curvilinear direction through the body of the rubber crown midway between the base of the porcelain crown and the palatal margin of the root, as represented in Fig. 185. All that portion of the pin imbedded in the rubber should be barbed, and long enough to ex- tend quite through the body of the crown. Contour the case posteriorly with wax, remove thoroughly the supporting wax in front, flask, pack with rubber, and vulcanize. ROOT CROWNING. 291 In the finishing and final contouring of the crowm, the rubber extension embracing the root may be made quite thin—but little, if any, thicker than the ordinary gold ferrule. Before placing the crown, a small hole should be drilled through it on each side near the platinum pin for the escape of surplus cement. The method of attaching the crown to the root with cement does not differ from that practiced in setting the ordinary ferruled crown. Before this is done, the centre pin should be sharply barbed or serrated. The two small openings near the pin, after a few days, should be closed with gold. Fig. 185 exhibits a sectional view of all the parts in their relation to each other.* The method is simple, inexpensive, and practicable, and requires no instrument or appliance not found in any fairly-well equipped laboratory. The process requires but two sittings—the first for. the preparation of the root and the impression, the second for final adjustment of the finished crown. By substituting a gold ferrule for the tempo- rary platinum tube used in securing the dimensions and con- tour of the root, taking the impression with the ferrule and centre pin in place, and transferring them both to the plaster model, a porcelain-faced, gold-banded, rubber crowm can easily be constructed by processes very similar to those already de- scribed, differing only in forming a matrix in the model for the rubber band. All-Porcelain Crowns.—Dr. Y7. G. A. Bonwill, of Philadelphia, Pa., contributed to the third edition of this work, in 1880, the following article descriptive of a method of root crowning which he designated a "New Method of Substituting an All-porce- lain Crown upon any Root in Either Denture," Dr. Bonwill's long-continued, intelligent and successful experimentation in this special department of practice is well known to the pro- fession, and the following, together with some important sup- plementary matter contributed since that date, and herewith appended, may be accepted as embodying his best and latest * The figure is faulty in that it represents the rubber as extending into the enlarged opening in the root, whereas it rests directly upon the dressed end of the latter. 202 MECHANICAL DENTISTRY. experiences. The first named contribution embraces the fol- lowing account of the method:— " No argument is needed to convince the advanced practi- tioner that some method is demanded whereby the thousands of good roots now sacrificed can be made permanently useful. Notwithstanding the great revolution wrought by machinery and improved appliances for filling teeth, so few are the suc- cesses that, unless some plants brought to our aid to save the remaining roots from the ravages of decay and from a want of skill and judgment by three-fourths of the dentists, we shall have little else than plates with which to meet the issue. Teeth can be saved without filling as well as by filling by some operators, but by a few only. Most of the dilemmas which all of us encounter every day are the results of bad dentistry. The plan to meet the difficulty must be one which is founded on such mechanical and physical laws that it can be safely relied upon for resisting both time and the various surrounding circumstances; one which any ordinary operator can follow, and which will be so cheap as to bring it within the reach of all; one which, if by accident the porcelain crown has been fractured, will allow of easy substitution in a few minutes without interfering again with the operation performed on the root. A crown is needed which can be obtained by every operator as easily as porcelain teeth for plate work, and kept in stock by him ready for any emergency, and costing but a trifle to replace; a method by which we can take any case of great irregularity, of any age and standing, and, without disturbing the root, cut off the crown and place the porcelain one in the proper curve in the "arch; a result which is absolutely clean, and which will make the patient feel safer from accident than any other process of restoration. " Has any such plan been generally practiced ? A few have been successful by certain elaborate methods which only the exceptionally skillful could perform, and even then, when a ' break-down' came, there was no alternative but to do it all over again, either at the cost of patient or operator. " Since 1871 I have been experimenting in this direction. The grand object in view was to give to the dentist at large ROOT CROWNING. 203 such a made-up aH-porcelain tooth as would meet almost any requirement. " My first plan (see Dental Cosmos, September, 1877) of a bolt and nut planted in the root by gold foil did not succeed, as the safety of the whole depended on the perfect rigidity of the bolt. Gold could not be so packed, save in a few cases. Amalgam overcame this difficulty, a platinum bolt being used instead of a gold one; but this operation was practicable only to skilled mechanicians; the average dentist was unable to perform it. " To meet this issue, the all-porcelain crown, without nut, was devised. In looking at the incisor crowns, superior and inferior, one might suppose that with so much cut away from their base, and with the pin-hole running entirely through the crown, the strength would be impaired. So I feared when the idea was first suggested to my mind. But upon trial the strength was found entirely sufficient. The experiments were made by drilling out old-style pivot teeth with a diamond. They are now made by the Trustees of S. S. Yrhite in special molds. YTith these still greater strength is attained. The incisors are so shaped as to form a dovetail, which allows the strain outward to come high up near the cutting edge, and not to depend upon the palatal base for support. The bicuspids and molars are cut out at the base, leaving a little more than a shell, with undercuts for the amalgam to act as dovetails. " This method leaves no joint on the natural root, and none in the crown, the operation being really an amalgam filling capped with porcelain. The hollow crown enables the operator to fit it in a very brief time, there being but little material to grind off. "If a fracture occurs, a new crown can be placed with but little fitting on to the old amalgam base, first buring off any excess. Ylien a case is presented where the pulp is not exposed, the hollow-base crown permits of so shaping the root as not to endanger the pulp, and to place the pins on either side of the same into solid dentine. At this time I cannot conceive of a single case occurring that cannot be met by one or the other of the plans herein described and shown clearly in the cuts,— equally adaptable where a number of roots are in continuous 204 MECHANICAL DENTISTRY. circle, or at intervals, or even for a full denture, as the teeth one by one give way; or in making the root of a lateral bear the crown of a central, or vice versa; or one or two adjoining crowns where no roots are left. Yrhere more than one crown is needed, the nut and bolt are called for, as in case of accident, or the necessity for readjustment, they can be unscrewed, the fixture removed, repaired in the laboratory, and again screwed in place. " Let me say just here that this plan of nut and bolt is ap- plicable where no roots are present, for fastening one or more plate teeth on a plate instead of by the method of Dr. Bing, in which, if the teeth are broken, they cannot again be readjusted. Such bolts with threads cut upon them can be inserted in any part of a perfect crown or a filled one by the use of amalgam, or gold, if one will use it in such cases. " Next in importance to a crown that will meet all cases are, the bolt which is intended to attach it to the root or roots, and the cement for securing it. " In such cases as are outlined in Figs. 190 and 191, see that the platinum pin is secure, and so placed where occasion de- mands that the lower part of the root need not be filled with cement, but that space be left for gases to escape through the tap-hole, which should be made obliquely from near the margin of the gum down below the cement, guarding against the lia- bility of decay again occurring at the cervical margin by beveling well the mouth of the cavity in the root. This once done correctly, there will be no need of again disturbing it. (Before setting the pin in any case the root should be tempo- rarily filled at the apex to insure against abscess.) Cases will present, however, where gases will form and escape. Here perfect security can be obtained by the tap-hole, as before de- scribed. This left open, a useful root is retained, and without any apparent unpleasant odor. Do not condemn an abscessed root. Such can be made equally successful where the perios- teum can be restored to health. Save every old root that has any length, and in which the pin can be well anchored high up, even if the walls are fractured for an eighth of an inch below the gum, or even where the root is split. In such cases ROOT CROWNING. 295 dovetailed holes can be made in each fractured part, and the amalgam will hold them together. Even without this, if the pin have a good quarter-inch anchorage at the very apex, it will be hard to dislodge. " To make doubly sure, when a tap-hole has to be made, that it is open from the apex, pass a fine thread of silk or cotton down alongside of the pin, build up the amalgam around it, withdrawing it after the crown is on and before the amalgam has set, holding the crown firmly while doing it. Or the thread can be introduced through the tap-hole and then passed up to the apex, withdrawing it when the crown is in place. This practice is perfectly justifiable rather than to lose a serviceable root. To a conscientious operator it needs no argument. In a very important root I go so far as to allow or even to force an abscess to form, and then treat it through the pulp-canal and fistula. I save seventy-five per cent, of such cases rather than abandon them. " Do not cut away the root very much, as a trifling space around the three-cornered pointed pin will permit enough cement for strength. Roughen the inner walls of the pulp-canal, and they may be left conical without danger of the pin being withdrawn. One very great satisfaction to the patient, as well as to the operator, is that the rubber-dam need never be used. The base of the root can be so prepared with a sharp bur that but little injury is done to the gum, and if it bleeds creasote or chloride of zinc will stop it; or, pressure of the thumb and index-finger against the buccal and palatal walls will stop it or any serous discharge while the root is being filled with cement. After that there is nothing to hinder the placing on of the crown. Be sure before forcing in the amalgam or cement that the apical foramen is closed. For this purpose I use fine zephyr saturated with creasote, except in cases where a tap-hole has to be made. " Only in cases of fracture of the shaft of a root would I use a band, and that should be placed on separately from the crown, not with it. Not a half dozen times in nine years have I had occasion to use such a band. The use of the platinum pin in the pulp-canal and passed high up obviates any necessity for 296 MECHANICAL DENTISTRY. such band, which is at best unsightly, and, for many other reasons, objectionable. Such a plan admits of no readjustment, and has been used by others only to assist the cement in setting. Cases occur where each root of a molar or bicuspid stands separated. One small pin in each well pressed up gives equally good results. " Never depend upon cutting a female thread in the dentine and placing a screw therein. This can be done, but it is so easy to be deceived that the plan as shown in Fig. 189. is much more desirable because more reliable. It is preferable in such cases to place in the pins and wait until the next visit of the patient, and, before placing on the crown, to try the pins to see if they are well anchored. Yrhen more than one crown is to be placed on in a continuous circle or line, cut off all the natural crowns at one sitting instead of finishing one at a time, as I once advised. As many as four incisors can be inserted at one sitting, though two are as much as one generally cares to adjust at one time. Where the crowns have been well fitted to a plaster model, there will be little difficulty in getting a good arch in the mouth, though a model is not necessary except for the superior or inferior incisors. If you have a large stock of bicuspid and molar crowns on hand, the fitting can be done at once. For special cases of very short teeth it would be well to have a plaster model. The only objection ever urged against using amalgam in the roots to secure the pins is that the gums soon look purple or blue. This can only occur where the joint is not high enough above the margin of the gum and where poor amalgam is used. Oxyphosphate or oxychloride of zinc can be used, but I prefer a special quick-setting amalgam such as I am using. Gutta-percha for such an operation is no better than putty. Some cases have succeeded with its use, but it does not at all meet the requirements. " As to the objection against amalgam that it is too plastic and too long in hardening, let me say that in fact such is not the case, unless the ordinary amalgam is used. I have never had to replace in a single case from such cause, where the amalgam I have adopted is used in the crown. For the roots, any first-class amalgam will do that does not take too long to ROOT CROWNING. 297 set. The safety is in having it not too soft in the crown when it is pushed home. Ylien the platinum pin is pressed up into the root with forceps, with the pin resting against the palatal wall of the tooth in incisors, there is no displacement. The pressure made on the crown ' squeezes' out all surplus mercury and impacts the amalgam well around the pin, and with a lump of it well pressed or pounded with small points around the pin in the crown from the outside orifice, it holds securely. " Yrhen amalgam is used, the shade of the crown should be rather lighter than if a white cement were to be used, as the opacity of the amalgam adds a blue tinge to it, just as in plate teeth the shade is made darker by the stay-plate, after sol- dering. " Fig. 186 shows the crown of a superior central from the palatal surface, the base cut out high, and with another coun- tersunk hole near the cutting edge, and undercut on the mesial and distal Avails, to allow the amalgam to grasp the body of the tooth well up, so that it shall not depend for support at the base only. The base may be cut aAvay after the amalgam has hardened and the crown would not fall off. The base is coun- tersunk to admit of easy and free adjustment of the pin, and to allow of a large body of amalgam around it, making one con- tinuous amalgam filling from the root through the crown, with no joint for retention of food, the material being stronger than the porcelain. The opening on the palatal surface is conve- nient as a safety outlet for the amalgam, and permitting the crown to go up to its place without obstruction. Y7hen the crown is well pressed up, the amalgam can be packed in around the pins, and the amalgam will act as a metallic base or back- ing for the palatal surface, thereby strengthening it. The thumb or index-finger on this orifice prevents the too free escape of amalgam when press- ing up the crowm. These crowns have no platinum lining or tubes as the English teeth have. They are stronger without them. A sectional view of a central is also shoAvn in Fig. 1S6, with barbed pin bent at the proper angle, the dark part showing the amalgam. 298 MECHANICAL DENTISTRY. " Fig. 187 shows a bicuspid with double pulp-canal, the cross- section of a crown with countersunk base, and the opening on the grinding surface for the escape of surplus amalgam. " Fig. 188 embraces sectional views of a superior and inferior molar, showing arrangement of pins, with a magnified view of the platinum pin, pointed at each end, made triangular and well barbed, the barbs looking toward the angle of the pin where bent. The perfected crown on the root shows the line of amalgam. When two or more pins are used, they need not be placed so far up in the roots or be so large in diameter as when a single pin is used. In cases where the root has to be tapped, then the pins can be placed in the mouth of each pulp-canal and the tap-hole made below, which should always be done before the pins are inserted, similar to Fig. 189, where there is Fig. 187. Fig. 188. a living pulp. Indeed, were it not for the fear of displacement before the hardening is complete, pins could be dispensed with in molars, as the body of amalgam is so great that when set it will hold sufficiently. The pins when set like a tripod at the base offer greater security than one alone. " Fig. 189 shows an all-porcelain crown, sectional view, where the pulp is still living. A hole is made on the buccal and lin- gual sides of the root as far away from the pulp-canal as possi- ble, and of size very little larger than the three-cornered pin, with an enlargement near the opening made with a barrel- shaped bur. The side of the undercut next to the crown should be as square as possible, not rounded, as in Fig. 189. In such a case the amalgam should be used quite dry, as the pins do ROOT CROAVNING. 299 not have to be pushed far, and can be wTell tamped in with narroAv steel blunt points, so as to make sure that the amalgam is solid. The crown can be placed on at once, or you can wait until the next day to see that the pins are all secure. " Fig. 190 is a sectional view of a case that requires tapping. The pin sIioavs its thin flattened edge, with space on either side for gas to escape from the foramen. It is pressed up about three-fourths of the length of the canal. " Fig. 191 illustrates the same case as Fig. 190, giving a view of the flat side of the pin and showing its bearing on either side of the canal, by Avhich it is prevented from lateral move- ment, the same as if the amalgam encased it all the way. The Fig. 189. Fig. 190. Fig. 191. gas escapes at the opening at A. (This opening should extend obliquely up to near the free margin of gum, and not as shown in the cut.) The amalgam extends no further into the root than A. This plan holds good in any tooth of one or more roots. " Fig. 102 shows views of a superior central incisor crown as made from a plate tooth (pins crosswise), backed up with heavy gold plate entirely to the cutting edge and down to the base where it rests on the root. The shape is given to the palatal surface by an extra plate, struck up concave with a round tool on lead and nicely fitted up to the backing on the 300 MECHANICAL DENTISTRY. buccal side, extending as high up as the angle or about up to the cross-pins, and filled in Avith scraps of gold plate and then soldered. The drilling of the hole through the base and the countersinking on the palatal side are done with the engine. The base of the plate tooth should be cut off from the pins down to the cervix to leave more room for the nut. The nut ordinarily goes much closer to the backing than is showm in the sectional vieAV of Fig. 192. The pin is barbed on its three sides and thread-cut on the end passing through the crowm. This is done Avith the ordinary screw-plate before inserting. For central incisors the pin of platinum Avire should be No. 16, and for small lateral No. 18. The nut is made of half-round or oval gold Avire, about three thirty-seconds of an inch in thickness. The hole should be drilled before cutting it off from Fig. 192. Fig. 193. the main piece, and a female thread cut in it by a tap made of an old excavator filed down and run through the hole in a screw-plate of the size of the wire to be used in the root. The slots in the head of the nut should be crucial, to admit of the screw-driver (Fig. 194) being used at each quarter of a circle. The nut should be tried upon the threaded part of the pin before being finally inserted, to see that no mistake has been made in the size of either the nut or pin. Such mistakes will sometimes occur. The pin is bent slightly, to allow it to pass through the hole in the crown and stand in the countersink equidistant from all sides, so that Avhen the nut is placed on it it will bear on all sides of the countersink alike, and the crown will not be tipped to one side. The pin, after the amalgam has hardened, can be bent with forceps to suit the countersink, ROOT CROAVNING. 301 taking care not to bruise the thread. The nut cannot be placed on at the same sitting, as the amalgam will not be hard enough to justify it. " If so unfortunate as to injure the thread, repair it with a little screAv-plate, as shown in Fig. 193. This may be made from a piece of steel di\dding-file, cut down to about the size shown in cut, and bent at right angles after heating it to a Fig. 194. cherry red, and aftenvard drilling a smaller-sized hole than the pin, through the short angle, and tapping it with the same tap used in making the gold nut, then tempering it to a dark straw color. This screw-plate can be run up on the pin in the root, and recut it its full length to the base. This obviates the removal of the pin after the amalgam has set. Taps and plates of various sizes should be kept on hand in duplicates. " Fig. 194 is a forked screw-driver, bent at right angles to Fig. 195. admit of getting into the palatal surface to put on the nut. It should straddle the pin and be only wide enough to cover the diameter of the nut. "Fig. 105 shows a case of irregularity which was beyond correction, on account of the poor character of teeth, their very ugly shape, their position in the palatal arch, and the age of the patient. In such cases I do not hesitate to cut off the 302 MECHANICAL DENTISTRY. crown, destroy the pulp, and place one of the plate-tooth crowns Avith a nut. To do so, the crown must be connected to the root by a strip of heavy gold plate, extending for a quarter of an inch or more, to bring the artificial croAvn into the circle. For such cases the all-porcelain croAvn will not do. The teeth can be separate or connected. I prefer the former. " The nut and bolt are best where a crown has to be very long and there is a close and deep underbite, with little room for the crown, Avithout being too full in front. The gold back- ing gives greater security, and should cover the whole palatal surface of the tooth. There are other special cases in Avhich this plan is to be preferred, but only for superior incisors or cuspidati. " This plan, as before suggested, I should use in attaching one or more teeth on a small plate, Avhere the roots have been lost, securing the bolt with amalgam to either decayed or sound crowns. " In this plan (Fig. 192) the pin is placed in the same as for all-porcelain crowns, and adjusted before it is set to suit the hole in the base of the crown, placing gutta-percha over the pin in the countersink until the next visit of the patient, Avhen it is removed and the gold nut placed on. All excess of amalgam around the margin of the gum should be removed, and before placing on the crown finally it should be warmed, and a piece of gutta-percha stuck on to the base and pressed up, making a water-tight joint when the nut is screwed up. " The illustrations are so accurate that it seems almost un- necessary to enter into any detailed direction as to the manner of procedure; but as it may help to perfect operations, I will do so in few words. " The root or roots having been prepared, and in readiness for the crowns, the canals enlarged, and the foramina closed, the platinum pin is cut off rather shorter than the length of the root, as it cannot be pressed up quite its full length through the amalgam. It is made three-cornered, and pointed at either end—more so at the root end—and Avell barbed with a sharp knife, as shown in cut, to and from the line between the crown and root, and bending the pin so that it shall impinge upon ROOT CROWNING. 303 the palatal Avail if for an incisor, Avhich will hold the crown firm while the amalgam is setting. " The croAvn having been adjusted to its place on the root, and all being in readiness, the canals dry, place soft amalgam entirely up to the end of the canal, and, when full, take a pointed, three-cornered excavator and run it up through the amalgam to force a way for the platinum pin. This latter is placed by grasping the pin with a pair of forceps, and gradu- ally pressing it up as far as it will go. A thin, flat-pointed tool can now be used to condense the amalgam about the pin. Be- fore this is done, the crown should be placed on to see whether the pin will permit it to assume its proper place. If not, the crown can be forced either way, and the pin will follow. The tamping around the pin can now be completed, and an excess of amalgam placed around it. The croAvn is now filled Avitli amalgam and grasped betAveen the thumb and index-finger, and pressed hard home. The opening on the palatal side of the croAvn can be filled Avith hard amalgam and Avell driven up about the pin, leaving a surplus for dressing when it is fully hardened. The excess of mercury is pressed out by the force used in driving it into place. Y^hen more than one pin is used, they can be filled in between on the grinding surface, and Avedged apart against the wall of the porcelain tooth, which Avill very much assist in retaining them. " This can all be done at one operation, although the pin can be placed in at one visit and the croAvn at the next. Y7here a croAvn has to be replaced from fracture, cut off the surplus amalgam around the pin with the engine and cutting-pliers until the new croAvn fits nicely. Fresh amalgam having been laid over the old amalgam, and the croAvn pressed up as be- fore, the repair is complete. The croAvns are not made to alloAV of their being pressed up over the end of the root, as in the Richmond plan of a gold band, as there is no necessity for the band, save in the feAV instances named in a former part of this article. " As to many little details, the practitioner can improvise to suit every case. I am of opinion that platinum wire is the best for the pins, although steel, well softened, will do if entirely 304 MECHANICAL DENTISTRY. covered with amalgam. The cost of the platinum is but a trifle more than the steel, and with it there is no danger of oxi- dation or of injury from the mercury." The following, reproduced from the Dental Cosmos, June, 1882, is the supplemental matter, before referred to, relating to the foregoing process:— " The numerous letters of inquiry received by me since the publication of my article on this subject in the Dental Cosmos for August, 1880, lead me to the recognition of two facts—first, that the said article was not as explicit as it should have been, having been too hastily Avritten to meet the next issue of the journal, and that my meaning has been misapprehended by many; and, secondly, that the methods then described were not as perfect, and therefore not as satisfactory, as those which I am now prepared to lay before you. Although I had been working at porcelain crowns since 1871, first using the nut and screw, yet I had had no opportunity offered me by a manufac- turer to place them before the profession. The demand which was created for the crowns by that article led to their produc- tion before the manufacturers had recognized all the necessities of the case, and they were not made correctly. " Besides some radical changes in the methods of attachment, there are various collateral advantages now to be availed of which were not then obtainable. The correct principle by which to shape the crowns is better understood by the manu- facturers ; a specially-adapted, quick-setting amalgam has been prepared; a proper pin to meet all the requirements and a device for forcing the croAvns into position are now furnished. The want of these things led to failure in many cases, but with such advantages as I have named there need be but feAV failures hereafter.......... " These all-porcelain croAvns have three distinctive features— a concave or countersunk base; a triangular opening from the base to a point at or near the cutting edge of the incisors, the base presenting to the labial surface (at its upper portion this groove is enlarged); a peripheral margin or border resting per- fectly flat on the root, the concavity of the base on the palatal side being at a much more acute angle than on the approximal ROOT CROWNING. 305 sides. An anchorage is made in the incisors by a depression or undercut betAveen the labial and palatal surfaces, opening on the latter. In the bicuspids and molars the retaining pits are nearer the grinding surface. " It is not necessary that the face of the root should be flat; it may either be concave or convex. I hope we shall soon have the incisor crowns made with the labial edge convex, to run up under the gum and conceal the joint. The concave base of the crown prevents the amalgam from escaping under the heavy Fig. Fig. Fig. Fig. Fig. Fig. Fig. 196. 197. 198. 199. 200. 201. 202. " Fig. 196.—Sectional view of an incisor crown as now made, from mesial side, showing the undercut at the point opening on palatal surface, the conical base, and the opening from the same to the retaining grooves, with the exact relations. " Fig. 197. —Palatal view of same tooth, a is the external opening for egress of alloy and for packing around the pin. The dotted lines around a show the recess or undercuts on the mesial and distal sides and near the point for retain- ing the crown, and its relation with the conical base. "Fig. 198.—Grinding-surface view of a superior molar with the countersunk pin-holes on the buccal and palatal sides. " Fig. 199.—Same view of an inferior molar with the pin-holes on the mesial and distal sides. " Figs. 200 and 201.—Sectional views of a molar and bicuspid crown, showing the countersinks and their relations with the conical base. " Fig. 202.—Sectional view of an incisor root, showing the retaining cuts made by the wheel-bur shown in Fig. 209. pressure exerted to force it into position, and in impacting the amalgam and expressing the mercury. It allows of a dense body of material around the metallic pin, giving the equivalent of a pin the Avhole diameter of the base of the crown. It leaves no joint, the crown and root being continuous. The amalgam is so thoroughly hardened at once by impaction in the double concave of crown and root as to make a very firm operation. It prevents any possibility of the crown's twisting upon the pin and root. In the event of fracture of the crowm, the convex 20 306 MECHANICAL DENTISTRY. surface of amalgam on the root makes the substitution of a new crown an easy operation. It enables the operator to fit the crown in much less time; it allows a proper position to be given to the pin, with less danger of fracture therefrom; it permits of a larger quantity of amalgam in the crown, and is capable Fig. 203. Fig. 205. Fig. 206. Fig. 207. Ftg. 208. Fig. 209. " Fig. 203.—End view of a canal prepared for the improved combination- metal pin. " Fig. 204.—End view of same canal, as in Fig. 203, prepared for a triangular pin, showing how much more of the mesial and distal surfaces have been cut away from it than in Fig- 203 for the improved pin. " Fig. 205.—*Sectional view of an incisor crown and root, with the improved pin in its relative position to each, with the depressions made by wheel-bur. " Fig. 206.—Sectional view of a superior molar, with the large angular pia in palatal root and two square pins in the buccal roots, one being shorter and not passing through the crown. " Fig. 207.—Block of a molar and bicuspid, showing the countersunk holes for pins in the molar, and the hole in the mesial side of the second bicuspid, where a pin is alloyed in and set into a decayed cavity in the distal surface of the first bicuspid, being held upon the molar roots and attached to the bicuspid by the alloy. " Fig. 208.—Side and end view of the largest size angular combination-metal pin with the stamped serrations. The square pins are without serrations and double-pointed, made of same metal and of equal thickness throughout. "Fig. 209.—The smallest-sized wheel-bur for grooving the canals for anchor- ing the pin and alloy. * The sectional views of the incisor and molar, giving the relative position of the pins in the crowns and roots, should show pins of larger size. The pins as furnished should be filed down but little. It is not absolutely neces- sary that so many serrations should be made in the canals by the wheel-bur for retaining the amalgam and pin as are shown in the sectional view of the root of an incisor. While there are no serrations shown in the roots of the sectional views of the molars, it is understood that all the canals must have the serrations. The square pins in the canal need no serrations. Just at the point where they occupy the countersink in crowns, make two or three very slight cuts on the edges with a sharp file. The ends can be left blunt. ROOT CROWNING. 307 of bearing greater strain; it makes the permanent success of the operation probable, from the fact that it is absolutely joint- less, and secures immediate solidity, even Avhile the amalgam is semi-plastic. These croAvns are capable of resisting the force of biting or mastication, because they are supported nearly to the cutting edge or grinding surface, the triangular opening from the concave base nearly to the cutting edge allowing the pin to be imbedded in the labial face of the croAvn where there is the greatest amount of porcelain. "A round hole, as heretofore used Avithout the concave base, Avould have its Aveakest point and relative strength through its centre, making the palatal base responsible for its retention. For incisors this one improvement cannot be overestimated. A porcelain crown othenvise would be too uncertain. YTith this nearly the Avhole of the palatal surface could be cut away. Without such an opening the pin would not go far enough past the base into the point of the croAvn to make them secure. To rely upon the base for retaining any porcelain crown would be impracticable, and much more likely to be immediately dis- placed before the amalgam hardened. The more acute angle of the base with the labial face is a marked improvement. There is seldom a necessity to give any further shape to the base as it now exists. The base should have its fine outlines preseiwed. " The pins, as now made, have marked advantages OArer the barbed triangular platinum pins. They are composed of a combination of metals Avhich, Avhile offering the greatest strength, allows the mercury in the filling to amalgamate the surface Avithout injury to their substance; the pin is retained in the root Avithout any serrations on its surface, which allows its easier insertion through the amalgam in the root. Serra- tions increase the size of the pin; are an obstruction to its passage through the amalgam; Aveaken the pin, making it more liable to break, and platinum Avill not amalgamate with the mercury. For these reasons I have long since abandoned their use. The size and shape of the pins I now recommend save time, have the greatest strength w'here the strength is most needed, and do not involve the cutting aAvay of so much of the 308 MECHANICAL DENTISTRY. mesial and distal sides of the root, nor present any obstacle to the successful packing of the alloy around them. Yhen the small roots of bicuspids and molars are to receive pins, square ones of a combination metal, without serrations, can be pressed up as far as desired. The irregular surface on the large an- gular pins is made when the pins are stamped, and does not weaken them as serrations do. They are rolled stiff and then stamped, thus securing the greatest strength. They admit of being placed at any angle, and if broken are much easier drilled out than a triangular serrated platinum pin. " The amalgam to be used as the medium of union must set quickly and be very hard. Thus far I have found nothing better than the alloys I have specially prepared for this line of Fig. 210. work, and, though they are costly, the superior results obtained by their use amply repay the cost. I use No. 1 entirely. If mixed thick, it will set so quickly that the operator must work rapidly to prevent its being wasted. " The simple device which I have called an adjuster (Fig. 210) is a very useful adjunct in the operation. It requires consider- able force to set one of these crowns according to directions— a force which cannot be applied with a mallet without danger of loosening or displacing the crown. Steady pressure with slight rotation will carry the crown into place, if the amalgam is not too hard or there is not too much of it. I would advise you not to attempt to set a crowm without one of these adjusters or its equivalent. ROOT CROWNING. 309 "A croAvn can be mounted upon almost any root if the alve- olar process has not been too much absorbed. In all cases the canal should be cleansed, and the foramen stopped Avith cotton or tin foil. If an abscess is threatened, drill an opening through the gum at the apex of the root. Of course, in an acute case it is safer to wait until the health of the root is established. " It is an advantage in every way to take an impression of the root, either with plaster or modeling composition, to get the size and shape of the crown. The articulation by a bite in wax is equally important. " Where much of the crown remains, the easiest way of cut- ting it off is to place a half-inch disk in the engine and cut through the enamel on the labial and palatal sides; then, with a spear-shaped drill, make several holes as close as possible in the groove, and with a small fissure-bur run them into one. It will easily break at this line. If the patient expose the gum much in speaking or smiling, the root may be cut down with the bur or corundum wheel beyond the free edge to con- ceal the joint. With bicuspids and molars it is not necessary to go beloAv the gum; a joint well made will not be observed, and the strength of the root will be preserved. If the root is decayed below the gum, after removing the softened parts, fill it with alloy; if it be split or have very thin walls, a platinum band can be made separate from the crown. This will seldom be necessary, as the pin, anchored high up in the root, will be its equivalent. " In preparing the canal, use first a small-sized, spear-shaped drill, carefully following the natural channel. Then follow with a larger one, taking care not to cut through the root near the apex. On the mesial and distal sides cut aAvay but little, as there is where fractures are most liable to occur. The canal can be very tapering and yet hold the pin, if the undercuts or grooves are Avell made all along the walls from the apex out. There need be but very little space around the pin. The mouth of the root should be countersunk the same as the base of the crown, in order that the amalgam may extend to its very edge, leaving no dentine exposed. The smallest-sized wheel-bur may be used to make an interrupted female thread at various points 310 MECHANICAL DENTISTRY. along the canal to hold the amalgam. By all means save all the Avails of the root possible. The face of the root may be flat or concave, according to indications. In most cases it had better be flat. " The crown to be inserted should be inspected closely, as the retaining undercut in the incisors and the depressions in the bicuspids and molars may not be well defined. If not, the crowns are liable to work loose. If the base has been ground off in fitting, the edges should be beveled again to a fine mar- gin with a corundum point. The croAvn should be fitted to the root in the mouth, not to the plaster cast. The articulation should be clear, to avoid displacement. The pin should be as large as the previously prepared canal will admit. The pin must in every case be fitted, and in fitting it file only on the plain sides. The serrations in the large pins need not be touched. Leave the end sharp, to offer the least resistance in passing through the amalgam. The end of the pin to be passed into the crown needs very little alteration. The croAvn being open on the palatal surface of the incisors, permits a blunt- pointed pin to go up to its place. The middle of the pin should not be interfered with if it can be avoided. It is well to cut the pin a little short for incisors, as it may not get pushed en- tirely up in the root through the amalgam. The small square pins are used in the bifurcated roots of bicuspids and in the buccal roots of molars. They can be sharpened at both ends, but the outer end will not require so much sharpening. The palatal roots of molars will generally take one of the largest thick pins, Avith one square pin in the largest and most accessi- ble buccal root; in both, if the canals can be reached to prepare them. Each canal should haATe a pin, even though one has to be so short as not to pass through the hole in the crowm. If it enters the countersunk base, it will support the root. The lower molars will require two of the largest-sized thin pins. As the support of the root is dependent upon the size of the pin and the depth to which it is inserted, the single-rooted teeth should have the very largest thick pin. If the root is thin on the mesial and distal sides, the thin, angular pin is to be preferred. When the pin is thoroughly set, it is hard to fracture the root. ROOT CROWNING. 311 The croAvn should go on easily and correctly over the pin, special note being taken of the position of the latter in the canal, so that it may be returned at the same angle. Ordi- narily these large pins do not have to be bent. If necessary, it had better be done Avith a hammer, and before the mercury touches them. The pin should have free movement in both root and crown. Should it be discovered that the pin is too long after it has been packed in the root, it can be cut off Avith sharp forceps, pressing them up against the pin to pre- vent displacement. It can be sharpened subsequently Avith the corundum Avheel. "To insure an amalgamation of the pin Avith the filling, brighten the surface of the former before inserting. In the buccal roots of molars the pins need not be inserted more than a quarter of an inch, or eATen less, in some cases. " The roots, crown and pins being in readiness and arranged on the table, so that no mistake may occur from getting the pin in the Avrong position, and the appliances necessary for the operation being at hand, the alloy preferred should be mixed a little thinner than if intended for a filling, especially Avhere the root has a long canal. The shorter the canal, the thicker the amalgam may be mixed. Mix only enough at one time for one root. Put enough amalgam in the canal to nearly fill it, but do not pack it; force a steel pin made for the purpose, of about the same size as the pin, to make Avay for the easier insertion of the latter. Then grasp the pin with suitable for- ceps, and carefully but steadily press it up to its destination. If you cannot succeed in doing so, remove it, and again use the steel pin. Ylien in place use an instrument with a point small enough to pass between the pin and the root, and pack by tamping the amalgam around it. A piece of bibulous paper placed over the point of the instrument will assist materially in carrying the amalgam before it. Before the amalgam has become too hard, replace the croAvn, to determine if the pin is in proper position; if not, it can be crowded to one side or the other Avith the tamping-tool. Should the pin be found to be rather long, it can be ground off with the corundum wheel, holding it, meanwhile, with the forceps. No attempt should be made to 312 MECHANICAL DENTISTRY. bend the pin after it has been amalgamated, for fear of breaking it. If any amalgam has been left, and it is still plastic, it may be packed around the pin at the base of the root, using the bibulous paper as before directed. If not, mix again to com- plete the operation. Bank up the amalgam on the root high enough to fill the base of the crown. The crown should now be tried on, and forced home with an adjuster adapted to the case, removing the surplus amalgam if too much, or adding if not enough. Remove and dry the crown, and fill up simply the undercut cavity near the cutting edge if an incisor, or the depressions in the crowns of bicuspids or molars, allowing a very little to extend into the cervical base. Now force it home with the adjuster. Free mercury will be squeezed out on the palatal surface, which should be wiped off. Now hold the crown in place with the fingers, with the bibulous paper under the tamping instrument, and consolidate the amalgam around the point of the pin in the crown, absorbing any free mercury which appears there. The excess of alloy at the joint must now be removed, care being taken to press the crown up while this is being done. The amalgam packed around the pin in the crown on the palatal side should be as stiff as may be to work readily. It is well to leave over some of the first mixing for holding the pin, and this will be about right for consolidating about this point. " If in a bicuspid or molar crown the pin should come so far through as to interfere with articulation, it may be ground off with the corundum wheel while the crown is firmly held by the fingers before the amalgam is hard. "The case can now be dismissed, with directions for the patient to return the next day, in order to make sure that the articulation is correct and to dress off the joint between the crown and root, which may be done with a small round- headed bur. " There are some cases in which the root cannot be filled Avith anything; if in a molar, the pulp-chamber can be relied upon to hold a headed pin or pins. Y nen a tap-hole is required in the root, it can be made low doAvn and at an acute angle, and the amalgam packed around the root-canal above the tap. ROOT CROWNING. 313 " Should an artificial crown be broken, another can easily be substituted by buring off any excess of amalgam, and using fresh amalgam, mixed thin, to allow of ready adjustment, " LoAver incisor roots, which have hitherto been abandoned to the forceps, can be crowned by this process. " The nut and screw process, as described in the Dental Cosmos for August, 1880, is now of but little value. It might be pre- ferred in cases of irregularity, Avhere the root is far out of posi- tion; but even here this new crown can be used in conjunction with the nut and screw without backing up a plate tooth, or where two crowns are to.be placed on one root by metal con- nections. " Two crowns can be inserted on the root of one large molar with the assistance of the decayed approximal surface of an adjacent tooth. (See Fig. 207.) " These crowns can be used for rubber or celluloid. In special cases, where plate teeth have to be backed with gold and at- Fig. 211. tached to rubber, they are beautifully adapted, and if one is broken another is easily substituted on the old pin. A heavy metal pin is packed into the rubber and passed partially or entirely through the crown, to which the crown may be vul- canized at once or afterward cemented on. " For repairing celluloid or rubber continuous-gum work, these crowns serve a useful purpose." Dr. W. H. Gates, of Philadelphia, contributed to the Dental Cosmos, March, 1882, the following descriptions explanatory of his method of setting all-porcelain crowns. The more recent forms of the latter, exhibited in Fig. 211, are similar to, if not identical Avith, those employed by Dr. BonAvill. The former's distinctive method of attaching these crowns consists in the use of a double cone-shaped, screAV-cut central pin set in amalgam. The following is the mode of procedure as described:— " With an unexceptionable crown at hand, and simple, prac- 314 MECHANICAL DENTISTRY. tical means for mounting, a new era has opened. The porcelain crown with proper complement is the consummation so devoutly wished for. Having as means of attachment a perfect junction by amalgam supported by a double-pointed screw, the root is thoroughly protected, Avhile the crown conceals the amalgam; and even the fine line of the periphery of the junction, since nature always provides a free edge to the gum, is not suffered to mar the beauty of the setting. " There is great gain in having the remains of the natural crown entirely removed, as they obstruct light and often the direct approach, both important factors in the successful treat- ment of the canals. In fact, Avhen Ave consider the great facility Avith Avhich a new crown can be mounted, Ave ought not to jeopardize the permanence of any root for the sake of retaining its imperfect crown. For instance, if the anterior wrall of a lower molar is not present, the curved mouths of the canals adjacent may be readily put in line with the deeper parts of these canals by free enlargement toward their anterior borders; but if that Avail be present, there is too much risk of penetrating the floor in the effort to cleanse and fill the canals. "Experience teaches that "roots filled carefully to the apex remain sweet and permanent without discoloration; but when simply smeared Avith creasote Avith but partial filling, as is so often done, the foundation is laid for future trouble. "After cutting the natural croAvn away, gutta-percha may be employed for support temporarily, or to reduce, if congested, the free edge of the gum. A root, for instance, quite hidden under a morbid gum may be uncovered in a few days by inserting a double-pointed screw lightly into its canal and pressing thereon a suitable portion of gutta-percha; but before inserting the screw a small vent should be made Avith a fissure-bur along the side of the canal, to remain until the root has been properly treated. Inexpensive gutta-percha will answer this purpose. The instrument and fingers should be moistened when using it to prevent its adhesion. If a pendent lobe of the morbid gum, however, occupies most of the cavity over the root, it is better to excise it at once with sharp scissors. "As with corundum disks, stump-wheels, and round points ROOT CROWNING. 315 the natural crown can be cut away as desired, it is often con- venient to leave the labial surface of front teeth standing until assured of a satisfactory result of the treatment of the pulp- canal— gutta-percha supplying a temporary contour. But Avhen preparing to mount the porcelain crowm, the natural one should be cut aAvay to the cementum, especially at the front surface—leaving the joint to occur at the base of the free edge of the gum. For this undercutting the dental engine is almost indispensable. Round burs moving from the gum cut safely and effectively, but Northrop's corundum points No. 6 cut more smoothly and in line with the gum. To finish, shape the end of the root concave; sink lateral, shallow pits or stay-grooves therein; ream out the canal to nearly once and a* half the thickness of the screAv, and make retaining pits in its stronger Avails Avith a safety-bur, e, Fig. 215. " Though the porcelain crowm is designed to reach the base of the free edge of the gum for greater strength and for the prac- tical concealment of the junction, yet, if the gum has receded from its normal position at the lingual aspect, only so much of the root should be removed at that part as will admit the crown to the position desired. " To fit the crown Avith accuracy and facility, a cast, though of the simplest character, is required.. The impression may be taken in the base of the crown itself filled Avith softened gutta- percha, care being taken to carry it against the root in the line of the position it is to occupy permanently. To form the cast, let the plaster extend from the impression so as to include an approximal surface of the crown, thereby securing a guide to the correct position. " If desirous of setting the crown at once, Avarm up the cast. remove the impression, indicate the root with a soft pencil and isolate it on the cast, excepting its connection Avith the guide surface, and the crown can be speedily fitted, the presence of the patient being required only to determine its proper length. If an additional sitting be preferred, the crown may be set temporarily or the gum supported by gutta-percha as before mentioned. In either case, when inserting gutta-percha into the enlarged canal, care should be taken not to compress air 316 MECHANICAL DENTISTRY. therein. To avoid this, let the stick of gutta-percha investing one-third of and extending someAA'hat in advance of the screw be smaller than the canal, so that upon insertion it shall first occupy the deeper portion, and then, as the screw is forced up, the air will be displaced. In fitting the crown to the cast use a heavy wheel to shorten, if necessary, any part of the basal out- line, cutting any Avay but outward, thus avoiding the liability of chipping the enamel. Cut the crown a trifle shorter than is required for proper articulation to allow for the amalgam joint, as when once set no grinding can be done except on its antagonist. " When the right length is assured, restore as much concavity to the changed base, as regard for its strength will permit. Do not make the edges so thin as to endanger chipping, and let the extreme edge be beveled at an obtuse angle, so that strength as well as the thinnest possible line of amalgam at the junction may be secured. " In mounting the crown, a double-pointed screw has certain important advantages. It forces the mercury out of the neces- sarily soft amalgam in the root as only a conical screw can, and leaves the amalgam in perfect condition. It presents a broader surface for resistance in the direction of the greatest strain, and it can be inserted with ease and facility in any position in the mouth. " Fig. 212 represents the screw as held by the carrier for insertion in all roots approachable in direct line. " Fig. 213 represents the screw with the parts of the carrier detached, showing their design and application. The perfo- rated screw receiver, made of steel, has a spring, b, acting outward, and a pin, b', to act in the slot, a', of the screw. When the screw with the end, a", inward is placed therein, and the spring compressed, it passes into the sleeve, c, Avhich, acting on the bearing, b'", and the jaws, b", prevents it from opening and also from turning. The front portion of the handle, d, is inserted into the sleeve, c, from the opposite direction, its pin, d'", entering the slot, c", Avhile its extreme front, d", passes into the screw receiver and acts against the end, a", of the screw, which fits therein. Thus the screw ROOT CROWNING. 317 firmly held is carried Avith direct force into the amalgam, and upon a slight withdrawal of the sleeve, c, by the shoulder, c'", the spring opens, and the screw is detached from the carrier. Fig. 212. Fig. 213. Fig. 214. oil °t " Fig. 214 shows the carrier modified to insert the screw at different angles. The hand shaft, e, acting through a collar from e' to its bevel gearing revolves the screw, which is freely held in any desired position by the handle,/, moving on a limited ball-and-socket joint at f. Ymen the screw is inserted into the amalgam, its release from the carrier is effected by slightly moving the front end of the hand-shaft, e, toward the joint,/'. " AVhen ready to mount the crown, select and place the screw in the carrier, and dry the prepared canal before mixing the amalgam. Mix the first portion quite plastic, fill the canal about two-thirds full, and insert the screw in rapid succession. See now by closing the mouth that the screw does not antagonize an opposite tooth, and by trying on the crown that it is central in its proper place therein. If not, immediately tamp, and, if necessar}', drive it AA'ith the tamping-arc, d, Fig. 215, to the correct position, and prepare next a second portion of amal- 318 MECHANICAL DENTISTRY. gam as dry as you can possibly make it cohere by rolling it with the index-finger in the palm of the hand. Cut the roll into thin slices, and, after removing with a flat burnisher the soft surface of the first portion, tamp the second in and around the screw with a tamping-ring, b, Fig. 215, which secures the screw immediately in the place adjusted. This ring and the arc, if grooved in the working face and inlaid with gold, will cut out appropriate portions of the prepared slices, and either or both may be employed to carry to and finish hard this dry amalgam in the outer end of the enlarged canal around the screw. Mix now a third portion of amalgam very stiff, place it in a tamping-cup (c, Fig. 215), pass it over the projecting end of the screw, and mallet it quite firmly around the base of the same. This cone represents the greater part of the amalgam that must intervene between the root and the porcelain crown, which is thus relieved of the principal strain in being set, and the stability of the operation is also assured. As the base of this cone extends to and anchors in the shallow stay-grooves previously mentioned, it may be trimmed down somewhat, if, by reason of shortening the crown in fitting, it should prevent the latter from freely taking its proper place. At this stage of the operation permit the amalgam to set for a half hour, and, if the crown be an incisor or cuspid, fill the retaining grooves, that the amalgam may be setting in them also. Mix the last portion thin, place a suitable amount as a lining in the base of the crown, try therein a cast made from the tamping-cup, and then apply with firm pressure to its place on the root. If there proves to be too much amalgam, remove the crown immediately, and with a sharp blade trim off from the middle to the apex of the cone such portion of its surface as may seem necessary. Replace, tap the crown into position with lead or wooden mal- let, and repeat if necessary. A little practice brings facility. Finish the palatal cavity with dry amalgam, trim away any excess at the joint with a small flat burnisher, and caution the patient not to use the tooth at all for a few hours. " In applying the porcelain crown to molars and bicuspids, it will rarely be necessary, with this careful manipulation of the amalgam, to insert more than one screw in each—that, of course, ROOT CROAVNING. 319 in the principal canal. The screw, made of platinized silver and being soon supported by its surface union with the amal- gam, is so strong, and its position so central, that amalgam alone properly extended to, and anchored in, the remaining canals, will add Avhat support is needed. The instruments sIioavh in Fig. 215, modified in construction, operate at all required angles. Rubber-dams are quite unnecessary, and it is of no consequence that the cone of amalgam should be kept dry while setting, as rinsing and drying it off Avith spunk restores a good surface upon which to build." Fig. 216 represents a device of Dr. M. L. Logan, by Avhich a central round pin is incorporated Avith the porcelain crown at the time of baking. To render the attachment more secure, the base of the croAvn is countersunk somewhat to afford addi- Fig. 216. Fig. 217. Fig. 218. Fig. 219. tional security of attachment. Fig. 217 exhibits the croAvn and root united. The above croAvn Avas subsequently modified by Dr. C. M. Richmond, Avho substituted a square pin to prevent rotation of the crown; and provided for the escape of surplus plastic ma- terial, on the application of the crown, through a vent or gate- way at the base of the latter, Fig. 218. Fig. 219 shows the crown in position. Methods of Mounting the Logan Tooth-Crown.—Dr. W. Storer How, of Philadelphia, says in a late number of the Dental Cosmos:— "As a condition precedent to the preferred procedure in per- manently placing an artificial tooth-crown, on a natural tooth- 320 MECHANICAL DENTISTRY. root, it is assumed that the root will have been properly treated, and the pulp-canal tightly filled at its apical portion. Such suitably prepared root or roots will, therefore, in all cases be instanced as subjects for the reception of Logan crowns in the following illustrated description of the best methods of mount- ing them. " Fig. 220 shows a superior right central root, an end appear- ance of the same, and a Logan croAvn, front view. Fig. 221 exhibits, at a right angle to the plane of the first figure, the same root, its end, and the Logan crown, side view. In both figures the pulp-canal is supposed to have been first drilled to a gauged depth with an engine twist-drill, No. 151, and then enlarged by means of a fissure-bur, No. 70, to the tapering form Fig. 220. Fig. 221. Fig. 222. Fig. 223. shown; the walls being subsequently grooved with an oval bur, No. 90. The enlarged section, Fig. 222, shows the crown ad- justed on the root by means of cement or gutta-percha, which surrounds the post and fills all the spaces in the root and crown. Fig. 223 shows the completed crown. Fig. 224 exhibits a bifurcated bicuspid root, its end appearance, and a Logan crown adjusted to the root. Fig. 225 illustrates the best manner of bending the post. Fig. 226 shows a split post, and its adapta- tion to a bifurcated bicuspid root is seen in Fig. 227. Figs. 228 and 229 exhibit the mode of mounting the Logan crown on a superior molar root, and Figs. 230 and 231 the same crown in its relations to an .inferior molar root. ROOT CROWNING. 321 " In the light of the preceding descriptions the figures clearly present to the mind's eye of the expert dentist the essential features of the new Logan crown and the method of mounting it; yet further explanation with reference to the figures will, perhaps, prove serviceable to such as may not be familiar with all the details of root crowning. Fig. 224. Fig. 225. Fig. .226. Fig. 227. " In every instance where a root is deemed ready to receive its filling, it should first be measured through its canal from the cervical opening to the apical foramen, and this may be accurately done with a gauge adjustable on a delicate canal explorer, Fig. 232. The same device serves to measure the distance from the apex to which the canal should be then filled Fig. 228. Fig. 229. Fig. 230. Fig. 231. (Fig. 233). It also gauges the depth to Avhich the drill may be carried. The proper degree of enlargement from the bottom of the drilled hole will, of course, depend on the obsenred size and character of the root, and every dentist should familiarize himself Avith generic tooth-forms, so that when the length of an incisor, cuspid, or other tooth-root is known, he can so nearly 21 322 MECHANICAL DENTISTRY. determine its hidden outlines as to form with precision a cor- responding enlargement of the pulp-canal such as is shown by the several cuts. The suitable preparation of the bifurcated roots of some bicuspids, and of all the molars, is a matter involving difficulties and judgment of an unusual character. An instance of the feasibility-of splitting the post of a Logan croAvn to adapt it to the bifurcated root of a bicuspid is shown by Figs. 226 and 227. This example directs attention to the peculiar shape of the new post,* in which there is effected such a distribution of its metal that its greatest strength is in the line of the greatest stress that will in use be brought to bear on Fig. 232. Fig. 233. Fig. 234. Fig. 235. Fig. 236. Fig. 237. the crown, while the least metal is found at the point of the least strain; the applied part of the post being in outline nearly correspondent to that of the root itself. The pulp-canal is likeAvise conformably enlarged to receive the largest and stiffest post compatible with the size and shape of the root to be crowned. " The fitting of a Logan croAvn to a root is best done by the use of a Avet stump-wheel in the engine hand-piece, Avhich affords the greatest facility for the slight touches required to * The writer disclaims any credit for its invention. ROOT CROWNING. 323 abrade the thin cervical borders of the crown, and that may thus be done Avithout encroachment on the post. " By the old method of adapting pivot teeth to roots, the close fitting of the crown precluded the use of a plastic packing, because its thinness over the surface of the joint made such packing liable to break loose under the shock and strain of use. The recess in the Logan crown obviates this defect by providing a receptacle for a considerable interior body of cement that will be deep enough to be self-sustaining internally, and yet allow the peripheral portions of the root and crown to approach each other so closely that, though only a film of packing remain, it will still be strong enough to insure the persistent tightness of the joint. Such annular boss of cement when formed of amal- gam also adds strength, in some cases, to the mount. " When enough of the natural crown remains, it is Avell to leave standing some of the palatal portion, and cut the root under the gum-margin at only the labial part, as shown by Fig. 234. Thus the labial joining of the root and ctoavii aa^II be concealed, and the other parts of the joint will be accessible for finishing and keeping clean (see Fig. 235). The Logan croAvn may be ground until a large part shall have been re- moved for adaptation to the occluding tooth or teeth without greatly impairing its strength (see Fig. 236). This croAvn, also, in such cases maintains the translucency Avhich is one of its peculiar excellences, owing to its solid porcelain body, and the absence of a metallic backing or an interior largely filled Avith cement or amalgam. " The distal buccal root of the natural superior molar is in nearly eA^ery instance too small to receive a post of any useful diameter, and, therefore, the Logan superior molar crown has but two posts, Avhich, like those of the inferior molar croAvn, are square, and thus may be easily barbed, as may also the ribbed posts of the crowns for the anterior tooth-roots. These posts are in all the Logan crowns large enough to ansAver in any given case, and can, of course, be easily reduced to suit thin or short roots. "Any of the cements or amalgams may be used in fixing these crowns, but good gutta-percha, softened at a low heat and 324 MECHANICAL DENTISTRY. quickly wrapped around the heated crown post, which is at once seated in the root, forms the best mounting medium, and has the great advantage of permitting a readjustment, or, if need be, the ready removal of the crown by grasping it with a pair of hot pliers or forceps, and holding it until the gutta- percha is sufficiently softened. "An excellent combination for some cases is accomplished by fitting a narrow, seamless gold collar over the neck of a root prepared like that of Fig. 235, and then adjusting and mount- ing in the manner described a Logan crown, with the result shown by Fig. 237." CHAPTER VI. BRIDGE-WORK. This method of substitution contemplates the filling in of edentulous spaces Avith artificial crowns by a process Avhich dis- penses altogether Avith the use of the ordinary base-plate, the appliance, in most cases, being permanently fixed in the mouth by attachment to one or more of the adjoining natural crowns, to the roots of teeth, or to both conjointly. Considerable diversity of opinion exists as to the advisability of permanently fixing such appliances in the mouth. Promi- nent among the objections urged is, that, in the event of acci- dent to the porcelain crowns, a danger to which they are constantly exposed, there is no practicable or sufficient remedy Avithout detachment of the entire framework to Avhich the teeth are attached. It is further objected that such a fixture, inca- pable of removal for cleansing purposes at the option of the wearer, must ultimately become not only offensive from the accumulation and retention of oral debris incapable of adequate dislodgment, but a source of serious injury to the remaining natural teeth, a result necessarily following the prolonged re- tention of alimentary substances exposed to conditions so favorable to fermentative or putrefactiATe decomposition. On the other hand, competent, intelligent, and conscientious operators, who are presumably well qualified from observation and experience to form a just estimate of the merits or demerits of the method, bear equally positive testimony in unqualified commendation of its superior excellence when skillfully per- formed under conditions that justify the operation, and claim for it as complete an exemption from the alleged objections as obtain in the use of any other mode of replacement in similar cases. A longer and more general experience at the hands of competent operators "will either confirm or discredit the present claims made in its behalf. More recent devices, Avhich make the removal of the appliance practicable, may obviate some of 325 326 MECHANICAL DENTISTRY. the objections which attach to fixed pieces, but it must for the present remain an open question whether these modified forms do not introduce new elements of mischief to neutralize any advantages attending their optional removal from the mouth. Among the simpler forms of substitution Avhich may be prop- erly classed under the head of " bridge-work," is the one in Avhich a single artificial crown derives support from attachments made to one or more of the adjoining natural teeth, originally by a process of cavity-filling. The original conception and practical application of such a method of supplying an eden- tulous space is attributed to Dr. B. J. Bing, of Paris, France, butAAThose method of operating has since been greatly modified. One of the earlier experimenters in this mode of replacement was the late Dr. Marshall H. Webb, Avho thus describes his method of operating in these cases:— " The insertion of a crown without plate or clasps where no root remains is a difficult operation, but when well performed, and the croAvn attached to teeth that are firm in their sockets, it is both satisfactory and permanent. " The first such operation performed by the writer was com- pleted February 12th, 1873, and the croAvn now remains as firm as when inserted. The operation was performed in the follow- ing manner: After suitably forming the cavities in the proxi- mate wall of each tooth next the space left by the loss of the one that had been extracted (unnecessarily) some years before, an impression of the parts was taken, and a plain porcelain crown was selected, fitted to place and backed with gold plate (18 c). A portion of the backing extended about one and a half lines from each side of the croAvn for insertion in the cavities prepared in the adjoining teeth, and to these parts a gold wire was soldered to fit into the pulp-chamber of the cen- tral and lateral incisors. A small gold plate was then formed to fit upon the gum, covering as much space as was taken up by the neck of the natural tooth. Yrhen the backing was riveted to the pins in the porcelain and this placed in position, and while the whole rested on the small plate upon the gum, the backing and plate were so secured by Avax that they could be removed intact, and, after being placed in a matrix, BRIDGE-WORK. 327 soldered. Each extended side of the backing and the surface of the Avire Avas barbed with an engraver's lossing tool, so that the gold foil would the better secure the crown when filled into every part. " The porcelain, with the gold attachments, being ready for insertion, a piece of light medium rubber-dam was put in place on two teeth each side of the space to be filled, and over the gum upon which the crown was to rest. (The rubber takes up but little space, and this is more than compensated for when the ligature—waxed floss-silk—is pressed to or near the neck of each adjoining tooth.) Oxychloride of zinc was then placed in the pulp-chamber of the central and lateral incisors and the crown at once pressed to place. When the cement had hard- FlG. 238. ened sufficiently to safely admit of further progress in the work, a portion of it was cut away from around the wire so as to make proper anchorage for the gold. Small pieces of light cohesive gold foil Avere then impacted around part of the wire and that portion of the plate extending into the cavities, and the crown was thus secured. The porcelain and gold attach- ments as prepared for insertion and the crown in position are illustrated in Fig. 238. " The cavity in the central incisor was extended to the cutting edge of the tooth, that access might be had to the wire and both sides of the plate; foil could not otherwise have been put in place, unless a portion of the labial margin of enamel were cut 328 MECHANICAL DENTISTRY. away, and this would have been objectionable because of the exposure of gold. A small part of the labial' instead of the cutting edge of the enamel of the lateral was removed, for the reason that there is not such a body of tissue as to safely allow it to be cut away to the same extent as in a central incisor. The margin of enamel Avas so formed, and the foil so inserted and finished; however, that, though the gold can be seen, it is not conspicuous. " While the operation just described has thus far proved suc- cessful, yet there is a possibility of the porcelain being broken from the platinum pins which hold it to the gold plate. To avoid such an accident a groove should be cut on each side, and along the cutting edge of the porcelain (Fig. 100, b), that gold foil may be impacted into it, after a heavy backing of Fig. 239. Fig. 240. gold plate and the Avire have been fixed in place and soldered. After the groove has been cut in the porcelain with a fine- edged corundum disk, one with an edge of the diameter of the gold wire selected for the case should be used to make a groove across the porcelain between the pins (Fig. 239, a), into which the wire to connect the artificial crown with the natural teeth is to be placed (Fig. 239, b), either beneath the plate or so that the edges of the latter may be joined to it, as the neces- sities of the case may require. "A starting-point should be made either between the gold backing and porcelain, or between this and the Avire, and the latter firmly fixed in a hand-vise while the gold foil is being impacted with the electro-magnetic mallet. When the gold is properly and solidly placed in the groove and over the backing BRIDGE-WORK. 329 and wire, it not only aids in securing the porcelain, but the contour of the ctoavh can be nicely filled out, and the operation made durable and beautiful (Fig. 240). " The surface of the gold placed along the base of the crown to the edge of the porcelain, and Avhich is to rest against the gum, together Avith the palatal portion, ought to be properly formed and finished before the crown is put in place, and this should be done in the manner before described. There should be a little space between the wire and cervical wall in each tooth to which the croAvn is to be attached, and narrow pieces of light gold foil carefully placed in this part, between the wire and enamel, with small curved instruments, and with the aid of the mallet; the surface of the gold at this part at least should be smoothly finished with very narrow (TV in.) strips of fine emery- cloth before the rubber-dam is removed. " In cases where the pulp is living in one or both of the teeth to which an artificial crown is to be attached, the heavy gold plate or the wire must be so arranged as to fit as accurately and to be made as secure as possible in the cavities prepared for them. In some cases, and where the form of the cavity admits of it, it is better to adjust and solder a small gold plate to the end of and at right angles with the wire attached to the crown. This plate should be so formed and beveled that gold foil can be solidly placed over the surface of it next to the artificial crown, and into the groove made around the cavity in the den- tine along the boundary line between this tissue and the enamel. When all is in readiness for the operation, oxychloride of zinc should be placed in each cavity and the crown immediately put in place, and very carefully held there till the cement has so crystallized as to secure the ends of the Avire and plate; about an hour is necessary to perfect such crystallization as to safely admit of the preparation for and the packing of the gold foil. The oxychloride of zinc should be left between the little plate or end of the wire and bottom of the cavity, and all parts where gold cannot be well placed; this preparation also protects the dentinal fibres from thermal changes. " One of the most satisfactory operations the writer ever per- formed was the insertion of a croAvn where a cuspid root had 330 MECHANICAL DENTISTRY. been extracted (unnecessarily), and the lady subjected to the wearing of a gold plate for some time. This crown was prepared and the contour filled out with foil as described (and as illustrated in Fig. 240), but gold wire, No. 13, was attached to and built in with the porcelain, and placed into the pulp-chamber of the adjoining lateral incisor (which had been filled), and this same wire extended from the anterior to near the posterior proximate surface of the first bicuspid tooth, the pulp of which remained in normal condition. The crown was placed in position with oxychloride of zinc, and cohesive gold foil Avas then impacted with the electro-magnetic mallet around a portion of the wire in the root and into the cavity in the crown of the incisor, and Fig. 241. also into the cavity in each proximate wall of the bicuspid tooth, as well as around and over the wire, joining the two fill- ings through the enlarged fissure. " The most extensive operation of attaching a crown to ad- joining teeth was performed by the writer before the Pennsyl- vania State Dental Society, at Delaware Yrater Gap, in July, 1879. In this case disintegration had taken place in many of the teeth, and cavities of decay had been prepared and filled from time to time. The teeth were abraded and the dentine was exposed along the entire cutting edge of each tooth that oc- cluded with another. The right upper lateral incisor had been BRIDGE-WORK. 331 lost twelve years before. The crowm of the left cuspid tooth was missing, and but a small portion of the enamel and den- tine of the first bicuspid upon either side remained. These last Avere, of course, pulpless, as also were the right cuspid and central and left lateral incisor teeth, and the pulp-chamber of each of these had been filled. All the operations made neces- sary by the abrasion and fracture of enamel from time to time, and because of imperfection in the fillings before introduced, were performed previous to the insertion of the crowm in the space left by the loss of the lateral incisor, and, as this crown and each cavity and pulp-chamber was prepared for the gold, all appeared as here illustrated (Fig. 241).* " Gold wire (No. 13), with a sharp thread cut upon it, was screwed into the dentine, and, at the same time, all the inter- stices between the tissue and the gold were filled with oxychlo- ride of zinc. When crystallization had taken place, some of the cement and dentine was removed from around the wire Avith a small bur, and a groove was cut in the dentine near the margin of the root so as to secure proper and sufficient anchorage for gold; cohesive foil (principally No. 30) was impacted into these parts, and the entire contour of the crown was restcred with the electro-magnetic mallet. This crown was not faced with porcelain, because the teeth of the gentleman for whom these operations were performed are but slightly exposed to view; and then, too, the gold had to be placed over the enamel to support and protect it along the cutting edges of all the incisor and the cuspid and bicuspid teeth. A gold screw was placed in the pulp-chamber and extended into the crown of each bicuspid tooth (Fig. 241). The apical foramen of each pulpless tooth was closed, and the whole of each pulp-chamber into which a wire was not placed was filled with gold. With a properly adjusted electro-magnetic mallet, carefully guided, and operated with a full current of electricity from a freshly-charged four-cell Bunsen battery, the contour of each crown was restored with gold, made solid and perfect throughout; the foil Avas placed in the same manner over the finely pre- * The cut (Fig. 241) illustrates the case well, though there are parts and grooves in which to anchor the gold that are not distinctly shown.—M. H. W. 332 MECHANICAL DENTISTRY. pared margins of enamel, and these were not marred in the least (Fig. 242). " The lower incisor teeth had so changed after the loss of the upper lateral that they almost closed upon the gum. This was partly owing to the abrasion of the remaining teeth, and in part due to the lower incisors gradually rising in the alveolar pro- cess. Because of such occlusion of the teeth a porcelain crown (plain ' plate tooth') with ' cross-pins' was used, and fitted and soldered to the gold wire, there being no space for a backing of plate. When the wire was prepared, the porcelain grooved and fitted to it, and ready for the placing on of the gold foil, the wmole appeared as illustrated (Fig. 241); the wire extending into each root about four lines. The cutting edge of the por- celain was removed to the same extent as that of the abraded and prepared incisors, so as to present the same appearance and Fig. 242. have the gold support and protect the remaining part. The wire of the crown was held in a hand-vise, while cohesive gold foil was placed solidly in the grooves, around the wire, over the cutting edge of the porcelain, and the entire contour restored with the electro-magnetic mallet. During the final fitting of the crown, it was made to so rest against the gum that the blood was pressed from the capillaries of the part. When ready for insertion, a light medium rubber-dam was applied to two teeth each side of and across the space which was to receive the crown; small barbs were made all around the wire with a sharp knife, and oxychloride of zinc was then placed in the pulp-chamber of the central incisor and cuspid, and the crown at once pressed to place. After it had been in position an hour, to allow of complete crystallization of the cement, portions BRIDGE-WORK. 333 of this and of the dentine were removed with a small bur so as to better secure the crown and obtain anchorage for the gold foil then to be put in place around the Avire, into each cavity, and over the prepared margins of the enamel. Principally No. 30 gold (one-quarter ounce cohesive foil) was used in this case, and all was impacted with the electro-magnetic mallet, except a feAv pieces of light foil placed in the space between the wire and cervical wall, and even these pieces were gone over Avith this very valuable instrument after they were in place. YTith Fig. 243. a o a, b, d, f, g, and h, pulpless teeth ; g, whole crown restored with gold ; a, /, and h, almost entire gold crowns ; the teeth, b and d, support the gold crown faced with porcelain, c, and fully one-fourth of the crown of each of these is restored with gold, as is also that of e, the pulp of which is living. this and all the operations completed, the case appears as here illustrated (Fig. 243). "All those who have the ability and who will work earnestly and conscientiously to properly perform the various operations described, and do their very best in every case, can so manage their practice as not to make it necessary for any of the patients they have charge of to wear artificial crowns mounted upon plates." 334 MECHANICAL DENTISTRY. Dr. Yrebb's method of operating in these cases was, to some extent, subsequently modified as follows:— " The method, modified and followed by the writer since per- forming his first operation (February, 1873), is quite different from the mode adopted in inserting the first crown, Avhich was prepared somewhat according to Dr. Bing's plan, and, though the work is more difficult, yet the improved crown is stronger and more complete, cleanly, and beautiful than when gold plate is simply riveted and soldered to the porcelain. It was to avoid such an accident as the breaking of the porcelain from the pins that the writer modified the method of preparing and inserting crowns. Among the changes made were those of making a groove (though not cutting it too deeply) in each side and along the cutting edge of the porcelain, and placing gold foil solidly in the groove and slightly over the cutting edge, to make the porcelain more secure than when the platinum pins alone hold it, and to protect the edge from the occlusion of the lower teeth; also, to build the crown into the approximal surfaces only. After the wire has been fitted to the adjoining tooth or teeth, or properly placed in a root, and a heavy but rather narrow backing of gold plate has been riveted to the porcelain, and the parts are fixed together and soldered, the greater part of the preparation of a crown which remains to be made, and the whole of the building of gold foil about it, is done out of the mouth at whateA^er time may best suit the operator; but the work requires care, and must be skillfully and well done. A starting-point should be made either between the gold backing and porcelain or between this and the wire, and the latter must be firmly fixed in a hand-vise while the gold foil is being put in place and made compact with the electro-magnetic mallet. All croAvns should be prepared and finished in the manner described, with such change or addi- tional work as is necessary to place them on roots, or to attach them to single or to the two adjoining teeth where roots are missing. "Methods have been devised or adopted with the object of less- ening the time necessary to perform such operations, and making them easy and cheap by the use of amalgam or some other BRIDGE-WORK. 335 plastic material; but sufficient time must be taken, excellent judgment and ability are required, and the use of gold is necessary for the doing of really fine, beautiful, and permanent work. " When a crown is to be attached to one tooth alone, the oper- ation is not likely to be successful (excepting where a bicuspid crown is built into a molar tooth), unless the tooth which is to support the crown be a pulpless one, and then such an opera- tion can be made both durable and beautiful. To secure suffi- cient anchorage for the insertion of a crown in such a manner, therefore, it may sometimes be necessary to destroy a pulp; but this ought to be the last resort, and should be done only when calcification of the enamel and dentine is complete or appar- ently so. The end, if well attained, justifies the destruction of a pulp for the insertion of a crown mainly because of the bene- ficial results which follow. These are the longer preservation of the remaining teeth, the gums, and the aWeolar process in normal condition, or the prevention of the absorption of the hard as well as the soft tissues under, and because of the pres- sure of, plates—this loosening and loss of teeth sometimes occurring years before there is likely to be such solution of the lime-salts of the maxillary border and recession of the gum. " Yrhere a crown is to be built into one tooth only, a gold wire, no lighter than No. 12, should be used. It should be fitted as far up the root as it is safe to enlarge the pulp-chamber for it; but the drilling may properly be done only after every part of the pulp has been removed and the apical foramen has been carefully closed with small, narrow pieces of light gold foil, which must not be put in place so long as there is any irritation about the end of the root. " In the case here illustrated (Fig. 244), the wire is fitted in the root and bent to receive the crown, and the cavity is nearly pre- pared for the filling in of gold. The cuspid (as Avell as the other teeth remaining in the mouth) be- came so abraded as to expose the Fig. 244. 336 MECHANICAL DENTISTRY. dentine, so that the margins of enamel had to be prepared for the placing of gold over them, and Avhen the crown was built in place, they were carefully covered Avith, and are thus protected by, the solid metal. After the porcelain part of the crown of the lateral incisor had been fitted to the model and soldered to the wire (shown in Fig. 244)— this portion of the wire should be flattened somewhat in some cases—the groove was made around the porcelain; the foil Avas solidly built in place, and finished in the manner hereinbefore described, and the crown Avas then inserted and the contour of the cuspid tooth was restored with gold. (The root of the left central incisor remains, and the crown which is fitted upon it is prepared for the building on of gold foil; after Avhich it will be ready for insertion.* Y4ien this croAvn is put in place, the gold wire is to be surrounded with gutta-percha; but little of which is, or should be, needed in the pulp-chamber, because of the close fitting of the Avire in and of the crown upon the root. During this preparation, a plain ' pivot' crown is kept upon the root, held by wood and gutta-percha.) "When.the lateral incisor croAvn, in the case illustrated, wras ready for insertion, and the gold at the base, Avhich was to rest upon the gum, had been nicely fitted to it, and the whole of the gold was smoothly finished, a good-sized piece of light-medium rubber-dam was applied to the teeth (the cuspid and the central and lateral incisors) on each side of the space to be filled, and so arranged as to cover the gum and the root between these teeth. The crown was made to so rest upon the gum as to press the blood from the capillaries of the part, and thus prevent particles of food from getting under it. (While the thickness of the rubber-dam might, to some slight extent, prevent the placing of such a crown against the gum as firmly as it should be pressed, yet this thickness is compensated for by the pressing up of the gum when the floss-silk ligatures are placed about the neck of each adjoining tooth.) After all this had been done, and fine barbs were cut around *the gold wire Avith a sharp knife-blade, oxychloride of zinc was placed in the pulp- chamber of the cuspid tooth, and, while the cement was still * The groove is not distinctly shown in the cut (Fig. 244).—M. H. W. BRIDGE-WORK. 337 plastic, the crown was at once pressed to place, and for a few moments held there. "After the oxychloride of zinc had hardened sufficiently to safely admit of it, the cement was cut away from around the wire at such parts as would make proper anchorage for the gold. There was, and in every case should fee, a little space left be- tween the Avire and cervical wall to be filled with gold for the protection of the enamel at this part. Narrow pieces of light cohesive foil Avere first placed in this space with small, suitably curved instruments, and afterward solidified with the mallet; after which a little larger (though still narrow) and heavier (none over No. 32) pieces of folded foil Avere used for placing around and about the wire in the root, filling the cavity, restoring the contour, and covering and protecting the prepared margins of enamel: each piece of the gold being thoroughly cohesive and made compact Avith the electro-magnetic mallet. The surface of the gold placed around the wire between it and the cervical wall, as well as all that part near the gum, was smoothly fin- ished with small files and very narrow (y^-inch wide) strips of emery cloth before the removal of the rubber-dam; after which the remainder of the gold was made smooth and so trimmed down as to be sure of the proper occlusion of the teeth. The croAvn attached to the cuspid tooth was made just short enough to be free from the striking of the lower teeth. The operation was finished at another time with Hindostan stones, together with pumice upon fine wood made into suitable shape. " When a croAvn can be securely attached to one instead of two teeth, the time of building-in is lessened about one-half. The slight movement which takes place in the socket of the tooth supporting the crown is not interfered with as when two teeth are fixed together by the gold wire holding the porcelain. If it should afterward become necessary to perform operations upon the adjoining teeth, the rubber-dam can as readily be applied as before attaching the crown." Professor Darby, in commenting on this method, says:— " Dr. B. J. Bing was the first to call my attention to a method of building one tooth into the adjoining teeth by means of gold wires running from the artificial into the natural teeth. I have 22 338 MECHANICAL DENTISTRY. never seen any of Dr. Bing's operations, but Dr. Marshall H. Webb has called my attention to one or more in the mouths of his patients, which have done good service for years. I also have in my own practice one or more which have proved most satisfactory. " The cuts, Figs. 245-and 246, represent two cases where arti- ficial crowns have received their support from the adjoining Fig. 245. teeth. It is desirable to have a pulpless tooth for a neighbor, though I question if one would be justified in devitalizing a pulp to secure this end. In the cases presented, a piece of gold wire was soldered to the backing of the porcelain tooth, and allowed to extend well up the pulp-canal of one of the adjoin- ing teeth. After it had been nicely fitted to its place, the rubber-dam was applied and drawn tightly over the gum Fig. 246. between the two natural teeth; the canal of the devitalized tooth was then filled with oxychloride of zinc, and the tooth with its gold support pressed into position. When the cement had hardened, the bulk of it was cut out and the space filled thoroughly with gold. The other end of the bar was packed around with gold foil, and the cavity of decay or cavity of con- venience was filled in the ordinary way. BRIDGE-WORK. 339 "It is ahvays better to take an impression of the space and adjoining teeth at the outset, and then do the major part of the Avork in the laboratory. The gold wire which enters the root can be bent or shaped with the pliers when the patient presents for final insertion. " I would not be understood as saying that these operations can only be performed successfully where there is a devitalized tooth for a neighbor; on the contrary, I have seen teeth inserted in this way where both teeth were living, but the support which is to be derived from the long right angle of gold in the root is certainly a great security against accident, adding, as it must, great strength to the operation." Professor Wilbur F. Litch has greatly simplified the method of attaching a single crown to the adjoining teeth in the class of cases under consideration. The following is his latest de- Fig. 247. scription of the process published in the March (1886) number of the Dental Cosmos :— " Fig. 247 represents a typical case, in which a lateral incisor (crown and root) has been lost, the cuspid and front incisor, fully vitalized, and without approximal carious cavities, remain- ing in position. " To Make a Pin and Plate Bridge.—1. Take in plaster an accurate impression of the cuspid and incisor and the inter- space. From this obtain a plaster model of the parts. " 2. Make from pure gold, rolled to the thinness of 26, standard gauge base-plates, to be carefully adjusted to the palato-approxi- mal surfaces of the cuspid and incisor. These can be made by swaging on dies and counter-dies obtained from the model, but more conveniently by bending the gold into shape upon the 340 MECHANICAL DENTISTRY. plaster model and pressing and burnishing it into perfect adaptation upon the natural teeth. " 3. Select a plain plate porcelain tooth of suitable length, shape, and shade, and wide enough to fit easily into the interspace. Let the neck of the tooth rest lightly upon the gum. " 4. With pure gold or platinum make a backing for the porcelain tooth. " 5. Place the tooth thus prepared and the base-plates already made upon the cast, and accurately adjust the approximal edges of the base-plates to the backing of the porcelain tooth in situ upon the cast. " 6. When this adjustment is made, cement together the base- plates and backing with a brittle, resinous cement (resin, two parts; wax, one part; or sealing-wax will answer), and before the cement has fully hardened remove from the cast to position in the mouth, perfecting the final adjustment there. By this method much greater accuracy of adaptation is obtained, as the lines of length, width, and contour are too fine to be reproduced with absolute fidelity in a plaster model. In this part of the process too much care cannot be taken to have each piece of the appliance fitted with absolute accuracy to the surface for which it is designed. When this has been accomplished, throw upon the yet more or less plastic cement a stream of ice-cold water from an office syringe; this renders the cement perfectly brittle and incapable of bending. This done, immediately remove from the mouth and invest in a mixture of equal parts of marble dust and plaster-of-Paris. "7. After the investment has firmly set, solder the base- plates to the backing, and the backing to the platinum pins of the porcelain tooth, using as a solder 20-carat gold. Thus joined, the appliance will present the appearance shown in Fig. 251— A, representing the base-plate for the cuspid; B, the base-plate for the incisor; C, the porcelain tooth with its platinum backing; D, the points of union between the base-plates and backing. At these points the greatest strength is required, and it is im- portant that here a large amount of the solder should be placed. The porcelain tooth being usually thinner than the natural teeth, there is nearly always an angle or de- BRIDGE-WORK. 341 pression at the points indicated, in which the thickness of the gold can be considerably increased without interfering with occlusion. " S. For the purpose of attaching the denture as thus far constructed, drill a small cylindrical opening through the pal- atal surface of the enamel of the cuspid and incisor respectively. These openings should usually be placed about as indicated in Fig. 250, at C. D. Sometimes, owing to a close occlusion, or to the contour of the tooth, it is desirable that they should be located a trifle nearer the neck of the tooth. Each opening should be Avell undercut, but must not encroach upon the dentine far enough to endanger the pulp. In size the open- ings need not be larger than will admit a platinum pin-head, in diameter, corresponding to 13, standard gauge, with a shank of IS, standard gauge. Into each of these openings must be fitted a platinum pin of the size indicated. The head of each pin must be made thin and perfectly flat both upon its upper and under surfaces. " 9. In each of the base-plates make an opening correspond- ing in position to those in the natural teeth. Pass through these openings and cement in them the free ends of the plati- num pins. AVhile the cement is yet plastic, place the denture in position in the mouth, carefully pressing the pin-heads into the openings made for them, and burnishing the base-plates into perfect contact with the palatal surfaces of the teeth; chill the cement, remove and invest as before, and with 20-carat gold solder the pins to the base-plates, flowing upon them and the backing as much of the solder as may be necessary to give them the desired thickness and rigidity; the amount admissible largely depending upon the nature of the occlusion; a central thickness of about 21, standard gauge, being all that is really requisite for strength, while the edges can be made much thinner. " Fig. 248 represents the appliance without the pin. A is the porcelain tooth and backing; E, the base-plates; C and F, the openings for the pins. " Fig. 249 represents the appliance completed with the pins in position. 342 MECHANICAL DENTISTRY. " Fig. 250 represents the natural teeth and interspace B, with openings for retaining-pins, C D. " Fig. 251, already described, represents the appearance pre- sented when the bridge is cemented in position. " To Attach the Bridge.—To attach the bridge the best attain- able oxyphosphate cement should be used. It is desirable that it should set slowly. Thoroughly dry the teeth and denture; mix Fig. 248. Fig. 249. the cement to as thick a consistence as is compatible with perfect plasticity. A thick, viscid, semi-fluid mass is what is required. With suitable instruments, swiftly but carefully place the ce- ment around the head and shank of each platinum pin, and also in the openings in the natural teeth. This care is necessary in order to exclude all air-bubbles and thoroughly engage the pin-heads in the cement. They furnish ample retaining sur- Fig. 250 face, but none to spare. In packing the cement around the pins, the under surface of .the base-plates should at the same time be covered. " The above details being perfected, the denture is at once carried to position, and with broad-pointed, serrated instru- ments pressed firmly into place, the excess of cement, if of the proper consistence, freely oozing at all margins. BRIDGE-WORK. 343 " Too much care cannot be exercised in the cementing process. As every second of time is of value, all instruments required must be selected and conveniently placed before the oxyphos- phate is mixed. To secure the most rapid possible, and at the same time the most thorough, admixture of the phosphoric acid and zinc oxide, a thick plate-glass slab, four inches square, Avith a flat (not a concave) surface, should be used. The spatula should be of steel, thin and elastic, and six-tenths of an inch wide. With these implements the whole mass of cement, acid, and oxide can almost instantly be brought into union, the spatula being used as a muller. When a narrow and rigid spatula is used in mixing any considerable amount of oxyphos- phate, the process can be accomplished only in detail, portion by portion, much valuable time being thus lost, during which the setting process is every moment hastening to its completion and rendering the cement unfit for use in this or any other form of bridge-work. A large excess of acid will, of course, make a thinner and more slowly-setting mass, but a cement thus mixed is deficient in strength and too unstable to give good results. "A very troublesome obstacle to success in the use of the oxyphosphate cements will often be found in the temperature of the air, an elevated temperature so hastening those chemical changes upon which the hardening of these cements depends as to render their use almost impracticable. This difficulty is likely to occur only in the hotter seasons of the year, and can readily be overcome by placing the mixing-slab, as well as the acid and oxide bottles, in cold water until their temperature has been considerably reduced. " During severe winter weather too low a temperature also gives trouble, the acid and oxide, even when the former is in some excess, forming a powdery mass utterly unworkable, but which melts down into an almost fluid condition Avhen brought into contact with the warmth of a tooth in situ. A temperature betAveen 60° and 65° F. secures the best results in mixing oxyphosphate cements. "Application to Pulpless Teeth.—In the above description the vitality of the pulps of the cuspid and incisor has been as- 344 MECHANICAL DENTISTRY. sumed; but, as can readily be understood, the pin and plate bridge can be even more readily and securely placed when one or both pulps are devitalized, for the reason that, the pulp- chamber being empty, the pin-holes in that tooth can be made as much larger and deeper as may be deemed desirable, the size of the pin being, of course, correspondingly increased. In a devitalized tooth, too, the base-plates can be sunk into the pala- tine surface when they interfere with occlusions, as sometimes happens when the antagonism of the lowTer teeth is very close and the overlap is considerable. " Ordinarily, however, such interference is inconsiderable, and the difficulty can always be overcome either in de\dtalized teeth by the expedient just suggested, or by carrying the base-plates as far away from the cutting-edge as practicable, at the same time making them at the point of contact as thin as is con- sistent with strength; finally, if necessary, removing a slight portion of the cutting-edge of the occluding lower tooth. "As experience with this as well as other forms of bridge- work has fully demonstrated, a slight mutilation of a natural tooth is far less destructive in its ultimate results than is the wearing of partial plates, in the use of which pressure falls upon the gum tissue, with the ultimate effect of stripping it from around the necks of the natural teeth, thus denuding them of that protective covering, and exposing them to the ravages of decay, and it may be safely affirmed that in all applicable cases the pin and plate bridge accomplishes its pur- pose with the minimum of injury to the natural organs. " The small size of the retaining-pins may excite doubts as to the strength of the denture; but pins smaller in size constantly used for attaching porcelain teeth to plates, and in the upper incisor series these pins are much less advantageously placed for resistance to pressure than are those imbedded in the natural teeth in the process above described. " The weakest point in the bridge is not the pins, but the cement; but this, while not so strong as the fused porcelain which surrounds the pins in artificial teeth, is, as experience has demonstrated, just strong enough to resist all ordinary wrear and tear, without being so intractable as to render the removal BRIDGE-WORK. 345 of the denture for purposes of repair a practical impossibility by any method short of its destruction. " Even Avith a good oxyphosphate cement, the work of re- moval is one of no slight difficulty, and requires the exercise of so considerable an amount of force that no one who has had occasion to perforin that operation Avill question the security of any well-constructed specimen of this form of bridge. During an experience of some seven or eight years in their use, the Avriter has had but one or tAvo cases in Avhich the appliance became loosened, and only one in which it Avas detached out- right. In the latter case the bridge (constructed with the natural tooth of the Avearer instead of a porcelain substitute) had been firmly in position for more than a year, when the sudden Avreneh consequent upon biting into a very hard peach detached it. Being immediately replaced, it has since then (some two years ago) done good service. In such cases it is usually advisable to slightly deepen the undercuts in the pin-holes before replacing. " Repairing.—As in all other forms of bridge-work in Avhich porcelain teeth are used, the accident most likely to happen is the fracture of this brittle material. As the bridge does not yield under pressure as does a detached plate resting upon the compressible gum-tissue, this form of breakage is one to Avhich bridge-Avork is more than usually liable. For the pin and plate bridge the least difficult method of repair is to separate the tooth and backing from the base-plates by means of a Avatch- spring saAV, and then force off the base-plates singly, this being much more easily accomplished than their removal when united to the backing. Another tooth is then selected, fitted, backed, and soldered as before. "As a rule, the writer has confined the use of this form of bridge to cases in Avhich only a single incisor is missing, but he has successfully attached a front and lateral incisor to a cuspid and the remaining front incisor. Yrhere an unusual strain is to be expected, the retaining-pins and pin-holes should, when practicable, be made correspondingly large, or two smaller pins may be anchored in one tooth, which latter plan gives very great resisting power and renders removal in the highest degree difficult and laborious. 346 MECHANICAL DENTISTRY. "Porcelain Tips.—Figs. 252, 253, and 254 show how the pin and plate process may be utilized for the attachment of porce- lain tips for broken or decayed incisors when the appearance of gold fillings is obnoxious to the patient. A represents the porcelain tips; B, the space to be filled by them; C and D, the opening for retaining-pins; F and G, openings in the base- plates (E) for the pins. Fig. 254 shows the appliance with pins attached." The following are descriptions of methods of replacement known as " Bridge-Work " proper, which is but an extension or amplification of the principles involved in the construction and application of the pieces just considered. Dr. Dexter, in defining this method of substitution, says:— "The main principles of bridging are, broadly, to perma- nently place artificial teeth between remaining natural teeth and roots in such manner that the porcelain substitutes shall fill the spaces made vacant by nature, while resting upon and being held in place by the natural teeth; the porcelain teeth, in the older methods, resting with more or less pressure upon the gum, and in later methods being raised quite clear of the gum and supported by the natural teett or roots in the same manner that a bridge truss or floor rests upon its piers—hence the name given the operation." Under this head may properly be classed a process of replace- ment, described by Prof. Litch in connection with the " pin and plate attachments " as a means of support for single front teeth, a method of attachment which, he says, although chiefly appli- cable to the incisors, may be combined with crowm or bar bridges for molars and bicuspids. The following descriptions BRIDGE-WORK. 347 by Prof. Litch relate to a case in illustration of the special method of attachment spoken of:— " Fig. 255 represents a practical case in which the upper third molar and the first bicuspid (both without antagonizing teeth) were utilized for the attachment of a bridge made of gold Fig. 255. crowns with porcelain facings, to supply the loss of the inter- vening teeth. " Fig. 250) represents the case as prepared for the bridge. A, the inner cusp of the bicuspid cut down to allow the placing of a sufficiently thick crown-plate ; B, a cylindrical undercut open- ing between the cusps for a retaining-pin; C, the third molar Fig. 256. made uniform in size from neck to grinding surface, the latter also being considerably retrenched; D, the crown-plate of a partial cap, made of pure gold, soldered with 20-carat gold, and so constructed as to cover every portion of the tooth except its buccal surface, the free edge passing up under the gum; E, a 348 MECHANICAL DENTISTRY. retaining-pin adapted to the opening B; F, the gold cap for the molar. " Fig. 257 represents the bridge anchored in position with oxyphosphate cement. " In the above case it will be observed that there is a consid- FlG. 257. erable space between the bicuspid and cuspid. This made it readily practicable to give so considerable a thickness to the mesial wall of the partial cap as to hold it securely against the side of the tooth. Had the space been less, contact with the cuspid would have afforded the desired security. " Fig. 258 represents another case in which a bridge was Fig. 258. attached by a bar, partial cap, and retaining-pin. A is an upper second bicuspid (without antagonist); B, its'inner cusp cut down; C, opening for retaining-pin; D, second molar, with slot for bar; E, cuspid; F represents the partial facing; G, the retaining-pin; H, a molar crown of gold, with porcelain front; BRIDGE-AVORK. 349 I, a platinum bar attached to the crown (H) and made to fit into a slot (at D); J, a plain plate cuspid, heavily backed and strongly soldered to the partial cap, but left Avithout attachment to or contact with the cuspid. " Fig. 259 shoAvs the bridge anchored in position. " This case, after two years of wear, is still in perfect condi- tion and doing good service. As it Avas possible to keep the gold attachments, backings, etc., out of sight, the appearance presented is very natural. " The bridge shoAvn in Fig. 257 has been in use but a few months. " The absence of antagonizing teeth for the bicuspids in each of these cases Avas a favorable condition, as a considerable thickness could be given to the crown-plate Avithout any inter- ference Avith occlusion. YThen the conditions are not so favor- able, cutting doAvn the inner cusp to the required extent and sinking the opening for the retaining-pin to the necessary depth, are processes certainly to be, as a rule, preferred to the entire removal of the crown for the purpose of feruling the root for the mounting of a crown of gold and porcelain—a procedure, however, not by any means to be indiscriminately denounced, for in many cases it is in the highest degree advisable. " There is this fact to be considered in regard to the use of the partial caps here figured—that many patients can be in- duced to consent to their employment Avho would refuse to submit to more radical measures, and thus, even when the latter would be advisable, the former may be employed as a compro- mise, or even as a temporary expedient. Having once tested the advantage of a Avell-fitting bridge, the wearer is much more likely to consent to whatever measures are necessary to give it security and permanence. " In the cases figured, however, as Avell as in analogous cases, these qualities seem to be amply secured. In every instance in which the removal of a pin and plate bridge has been neces- sary, the film of oxyphosphate cement has been found intact, and the surface of the tooth upon which it rested perfectly protected from decay. The only exceptions to this rule have been the very feAV cases in Avhich one or the other of the retain- 350 MECHANICAL DENTISTRY. ing-pins has become loosened, the bridge being for some weeks still worn in the loosened condition. Under such circumstances the cement will, of course, become detached and wash out, admitting food and secretions; but so long as the appliance remains immobile—and that is its' normal state—the cement Fig. 259. rests undisturbed. It need hardly be claimed that its durability is without limit, although under a metallic covering it appears to be practically so; but under the conditions represented in the processes as above described, it is certainly good for many years of satisfactory service, and when it fails, through chemical Fig. 260. abrasion, it will fail first at the free margins, where defects are most easily seen and remedied." The following is a condensed account, by Dr. Dexter, of a method of bridging devised by Dr. H. C. Register, one of the earliest experimenters in this method of replacement. The BRIDGE-WORK. 351 distinctive feature, as also the special merit, of Dr. Register's appliance consists in the provision made for the ready replacement of broken crowns. The process is thus de- scribed :— " Taking a typical case (Fig. 260), a rim or saddle of gold, Fig. 261. platinum, or iridinized platinum is struck to fit the spaces betAveen the teeth A and B. To this are attached bars X (Fig. 202), to enter the fillings at Z, Z (Fig. 261). Posts or pivots (D, Fig. 262) are soldered upon this saddle where the artificial teeth are to be placed, their free ends being threaded to carry the nut E. Hollow crowns, countersunk for the nut at G, and Fig. 262. E 9 having the necks ground to reach over the saddle and press upon the gum, are fitted over each post. Amalgam is used to fill in the space between the post and the tooth-wrall, as in a Bonwill setting, and the crowns are drawn to place and held with the nut. The saddle is fixed in its place in the mouth, 352 MECHANICAL DENTISTRY. before the crowns are finally attached, by filling into the cavities Z, the bars X, X." Dr. J. L. Williams, of New Haven, Conn., has given to the profession, Avithin the past few years, a number of important communications relating to bridge-work, to Avhich space is given to such portions only as relate more especially to practical details. The initial portion of the following, reproduced from the January (1884) number of the Dental Cosmos, treats also of single crown replacement, and is embodied in this connection as having immediate and necessary relation to subsequent descriptions. The following are Dr. Williams' descriptions of his methods of crown and bridge replacement. "As the single crown is the beginning and end of all bridge- wrork, a description of that particular form which is of the greatest practical value in this work will first be necessary. This is known as the Richmond CroAvn, although not the crown which Dr. Richmond claims as his invention. It consists essentially of three parts: a square pin of plati- num and iridium which enters the enlarged pulp-canal, a cap of gold, and the porcelain face, which is the ordinary plate tooth. " This crown is made in the following manner: After the end of the root is made perfectly smooth with corundum wheels and properly-shaped scalers, a gold ferule or band is fitted around it. If it is desirable that this band should be entirely concealed, the labial surface of the root should be beveled a little above the margin of the gum, and after the band has been soldered it may be placed in position, and the line of contour of the margin of the gum marked upon the front of the band. The proper bevel can then be cut and the edges squared upon a corundum wheel, leaving the lingual portion of the band a little longer than the front. Pure gold, rolled to No. 34 of the standard gauge (American), is used for soldering upon the beveled surfaces, thus making a closed cap for the end of the root. A suitable tooth is now selected and backed Avith pure platinum or pure gold. The cervical end of the tooth is then ground to the pftmer position on the front bevel of the BRIDGE-WORK. 353 cap, all of the fitting being done Avhile the cap is in position on the root. "After the fitting is completed, the cap is removed, and the tooth attached by strong resin Avax and again placed in position while the Avax is warm. Any slight change in position Avhich Fig. 263. is necessary can then be easily made. The tooth and cap are now removed together, invested, and united at the back by solder. It is well to use a solder for the cap Avith a higher melting-point than that used for the backing, as it obviates the Fig. 264. danger of unsoldering the band when the backing is flowed on. After finishing and polishing the A\rork, the end of the root is made perfectly dry, a sufficient quantity of oxyphosphate ce- ment, mixed someAvhat thinner than for filling purposes, is placed in the enlarged pulp-canal and also in the cap. The 23 354 MECHANICAL DENTISTRY. crown is then carried to place with firm, steady pressure, and held a few minutes until the cement is sufficiently hard to pre- vent displacement. The surplus cement which has oozed out around the band should be carefully removed and the work is then completed. Fig. 265. Fig. 266. " The bridge-work is simply an extension of the crowns over spaces where the natural teeth have been lost. " Fig. 264 was drawn from a model of a case in practice. In this case the roots of the centrals are shown prepared for the Fig. 267. fitting of the bands, the laterals having been extracted. Single crowns are made for these roots precisely as I have described. They are then temporarily placed in position. Laterals are selected, backed, ground, and fitted to position. The laterals are then attached by means of strong wax to the centrals, care- BRIDGE-WORK. 355 fully adjusted in the position which we wish them to occupy, and the Avhole removed in an impression of im^esting material. An additional quantity of investment is mixed and poured over the exposed ends of the caps, and the Avhole alloAved to harden, after which the investing material is cut away from the backs of the teeth and crowns, and they are all united by soldering. " Fig. 205 shows the wTork completed, and Fig. 266 is from a model of the mouth as restored with the crowns. " In cases Avhere the space is occasioned by the loss of more than one tooth a somewhat different method of procedure is necessary. " Fig. 207 sIioavs a model of a mouth in which the superior laterals and centrals had been extracted. The canines were badly decayed, Avith exposure of the pulp. The first step is the remo\ral of the pulps from the canine roots as previously described. The crowns are then fitted as already described and placed in position. An impression is then taken in plaster, the crowns remaining imbedded on its removal. The impression is varnished and oiled, and a model of investing material poured. After this has hardened, the impression is carefully cut aAvay, and we have a model of the mouth Avith the croAvns in position. A 'bite' is taken and the articulation secured in the usual manner. The re- maining crowns, having been backed, are fitted, and the face of the work imbedded in investing material. " The whole piece is noAV united at the back by soldering, and when finished presents the appearance showm at Fig. 268. " Fig. 200 sIioavs a model of the mouth after the bridge has been cemented in place. " Fig. 270 is an illustration of a piece of this work for Avhich there is a very frequent demand. It is for supplying the loss of the first molar and bicuspids. If the canine is intact, the anterior end of the bridge may be attached by a strong band of clasp metal passing around the canine, partly beneath the margin of the gum, so as to present the least possible exposure. 356 MECHANICAL DENTISTRY. If, as is frequently the case, there is extensive decay, it will be best to excise the remaining portion of the tooth and replace an artificial crown as shown in the illustration. A gold cap is then Fig. 269. made for the second molar. If this tooth is decayed it will only be necessary to remove the decay, and the cement which Fig. 270. is used for setting the bridge will make the most perfect filling material beneath the gold cap (Fig. 270). The intervening molar and bicuspid crowns are made in the following manner: BRIDGE-WORK. 357 the porcelain faces, which are furnished by the S. S. Yliite Dental Manufacturing Co., are backed with gold or platinum and the tips ground squarely off. Zinc pattern-dies, an assort- ment of Avhich should be made from the grinding surfaces of molars and bicuspids, are used for swaging from pure gold a tip or cap for the protection of the porcelain face; for without this Fig. 271. protection the porcelains wrould be almost certain to be broken. The concave surface of these tips is filled by melting coin-gold into them. This surface is then ground smooth and fitted to the squared surface of the porcelain face and Avaxed in position. Triangular pieces of platinum are then cut of the proper size Fig. 272. to fit the sides of the tooth, Avaxed in position, and the whole invested, leaving the back open, Avhich is filled with coin-gold. " These teeth are then fitted into position in the bridge, as previously described (Fig. 272). " Fig. 272 shoAvs the completed work in the mouth. " AVhere only one molar or bicuspid is lost, sufficient support 358 MECHANICAL DENTISTRY. may be gained by the cap, which is made to pass over the adjoining molar. If the first molar and second bicuspid are lost, the anterior end of the bridge may receive sufficient support from a strong spur, which may rest in the groove or sulcus between the cusps of the first bicuspid; or this groove may be deepened into a cavity, into which the spur projects and around AA'hich a filling is placed (Fig. 273). " The most extensive pieces of this work which have been attempted are cases of twelve and fourteen teeth upon three and four roots. Several of these have been worn for a year or more, and none of which I have any knowledge shows any signs of failure. Fig. 274. " Perhaps I cannot better close this paper than with the de- scription of the restoration of a mouth where any attempt to remedy the ruin save by extraction would have been considered madness; and yet the lady for whom this work was accom- plished is, to-day, so far as appearance, utility, and comfort are concerned, enjoying as perfect a denture as any person who has the same number of natural teeth intact. " Fig. 274 was drawn from a model of the mouth as presented. Only one tooth remained, the pulp of which was not exposed— the left second superior molar. In the first bicuspid, canine, BRIDGE-WORK. 359 and central of the left side the pulps were exposed and in a partially putrescent condition. Abscesses had formed about the roots of the second left bicuspid, right central, canine, and second bicuspid. The pulp was slightly exposed and inflamed in the right first superior molar. The second bicuspid on the right side and both bicuspids on the left were extracted at once as worthless. The exposed pulp in the right molar was treated and capped. The partially living pulps were removed from the teeth above mentioned, the fistulous openings were healed, and all of the roots thoroughly cleansed, and plugged with orange- wood saturated with carbolic acid and glycerine. The greatest Fig. 275. difficulty was encountered in the treatment of the right canine root, which had two large openings through the side of it, and through Avhich projected into the enlarged pulp-canal a tume- fied growth of the pericementum. For several weeks the tissues around this root were highly inflamed, and the face was several times badly swollen. The difficulty was finally overcome by covering these openings with No. 30 gold foil, and filling the root with amalgam. Crowns were then fitted over all of the roots. A bridge was then extended from the left canine to the first molar to restore the lost bicuspids. The missing bicuspid on the right side was restored by attaching the crown to the 360 MECHANICAL DENTISTRY. cap Avhich was placed over the molar containing the exposed pulp. " Fig. 275 was drawn from a model of the mouth as restored. " In conclusion, I desire only to repeat what I have already substantially said, that this work opens up a neAv field for the usefulness of our profession, which will bring joy to the heart of every conscientious dentist. Its possibilities are almost un- limited." A continuation of the subject of bridge-work, with illustra- tive cases, by Dr. Williams, is contained in the December (1884) number of the Dental Cosmos. These descriptions are intro- duced here, accompanied by some preliminary comments on the antecedent treatment of the organs of support, a precau- tionary measure which all recognize as of vital importance, especially in connection with artificial substitutes immovably fixed in the mouth. The following is the contribution referred to, a portion of the preliminary matter being omitted:— " Knowing that the value of these artificial substitutes for the natural teeth is entirely dependent upon the conservation of the teeth or roots upon which they are mounted, and believing that the methods of treating these roots Avhich have been worked out in connection Avith the system known as crown- and bridge- wrork are superior to those practiced by the majority of the pro- fession, I am disposed to devote considerable space to this part of my subject. Before describing the several modifications of bridge-work illustrated in this article, I desire to call attention to a few of the cases which I have treated, and which are more or less radical departures from those ordinarily met with. " Case I. This case was reported in the Independent Practi- tioner for April, 1884, from which I quote as follows: ' Mrs. S. had been wearing a pivot-tooth on the root of the upper right central for several years, and as it required frequent re-setting she desired to have it replaced by a more permanent operation. On removing the crown the root was found in a bad condition. Decay had penetrated the side of the root, leaving quite a large opening into the pericementum. An enlarged foraminal open- ing led to a cavity at the end of the root, from which an offen- sive pus was discharged. But the root was very firm, and BRIDGE-WORK. 361 promised to give a secure foundation for a crown if it could be brought into a healthy condition. A little coAvardice prompted me to attempt the treatment through the root, but after a week's effort my ambition in that direction Avas satisfied, and I resorted to a method which has proved eminently successful in several cases of this character. The end of a soft, smooth broach Avas bent so as to form a little hook. This was passed up the enlarged pulp-canal until the hook slipped over the end of the root. The broach was then seized Avith pliers at a point exactly opposite the external end of the root and draAvn out, and the length carefully measured. "'A point of orange-wood was carefully shaped to fit the pulp- canal, a notch cut on one side, showing the exact length of the root inside, and after dipping in a solution composed of equal parts of carbolic acid, chloral hydrate, and gum camphor, it was driven into the canal until the notch appeared precisely opposite the end of the root. I knoAv of no other method by which an enlarged pulp-canal can be so perfectly filled, Avith a certainty that the filling material has gone exactly to the end of the root, and no further. "' The Avood point wras tAvisted of at a point about half the length of the root, Avhere it had been weakened by passing a knife around it, cutting partly through. Heavy gold foil was placed over the opening in the side of the root, and the large funnel-shaped opening filled Avith amalgam. An external opening Avas made opposite the end of the root, and the dis- eased bone and end of the root cut away Avith rose-burs. A cotton tent Avas kept in for two days. On the third day a croAvn was placed on the root, and in ten days the external opening healed and all irritation had passed aAvay.' " Case II. Mr. Yr. had a central incisor broken near the margin of the gum by a base-ball. The pulp Avas removed and the canal filled Avith gutta-percha. Inflammation folloAved and an abscess threatened, Avhich was prevented by removing the filling. AVhen he came to me the canal had been open for more than a year, and from it there had been more or less con- stant discharge. On examination I found it filled Avith black and very offensive matter, which had stained the dentine to a 362 MECHANICAL DENTISTRY. considerable depth. After syringing with warm water, I en- larged the canal materially and passed directly through the end of the root with a rose-bur. I enlarged the cavity which I found at the end of the root until I had produced quite a copious flow of blood through the canal. After the bleeding had ceased, a broach wound with cotton was dipped in chloride of zinc, tAventy percent, solution, and passed up through the root. After this treatment the canal was simply dressed with Lister- ine for ten days, the dressing being changed every day. At the end of that time, there being no discharge (in fact, I could not discover at any time after the operation that there Avas any discharge of pus), the root was filled precisely as described in the preceding case, and a Richmond crown mounted upon it. " I believe the most rational treatment for that persistent pathological condition which remains around the roots of teeth which have been the seat of alveolar abscess may be summa- rized in a single short sentence. If the source of the primary irritation remains, remove it; cleanse the root thoroughly and fill it; then reduce the territory of perverted physiological action to the condition of a simple wound, and treat it as such. If the case is one of long standing,-1 enlarge the external opening and enter the cavity at the end of the root with a large rose-bur, cutting out the walls of the cavity and trimming the end of the root. Syringe out with Avarm water; inject a ten per cent. solution of chloride of zinc, and insert a cotton tent for a few days. Dress the wound—for this is what you now have— daily, syringing with peroxide of hydrogen, followed by Lis- terine. I believe this simple treatment will cure the most per- sistent cases of abscess, or, more properly speaking, alveolar ulcers, in from ten days to two weeks. The medication of these ulcerated tracts for many weeks, and sometimes months, is neither humane nor scientific treatment. " While I have thus written encouragingly of the practice of retaining pulpless teeth in the jaws, I would always encourage the removal of healthy pulps, except when absolutely necessary. But the operator should not hesitate to do this wdien convinced that the patient will be greatly benefited by the insertion of a piece of work which necessitates the removal of a healthy pulp. BRIDGE-WORK. 363 However, the constant modifications and improvements in the methods of constructing the work are making the removal of pulps more and more unnecessary. " Y7e will now proceed to consider the principal object of this paper, Avhich is the illustration and description of some of these improvements. " Fig. 276 shows a piece of work made for a case of quite Fig. 276. frequent occurrence. It represents the restoration of the inferior bicuspids and first molar of the right side. A gold crown is made for the second molar, and then the three intervening teeth or ' dummies' are made as described in my former paper. For the support of the anterior end of the bridge the method hitherto practiced has been to excise the crown of the cuspid and fit a porcelain crown with gold backing to the root, and to this the anterior end of the bridge is soldered. " Fig. 277 illustrates a de- vice Avhich obviates the neces- sity for removing the cuspid crown. A gold band is fitted around the cuspid. At the • front, shoAvn at a, Fig. 277, this band is allowed to pass a little beneath the margin of the gum so as to make the smallest possible exhibition of gold. On the lingual aspect of the tooth this band is allowed to be nearly the length of the crown. It will be seen that when this band is fitted as perfectly as possible there must necessarily be quite a vacancy between the upper part of the lingual sur- face of the tooth and the band. It is important that this portion of the band fit the tooth perfectly, and an accurate adaptation is obtained as follows: A piece of pure gold, rolled to No. 35 Fig. 277. a. b. c. d. 364 MECHANICAL DENTISTRY. American gauge, is fitted over that portion of the lingual sur- face of the tooth which it is desired to cover, d, in Fig. 277, shows the shape that this little pure-golgl plate usually assumes. It can easily be fitted perfectly by the use of a burnisher, and then, with the band in position, a drop of melted resin wax is flowed into the space between the pure gold and the band. It is now removed from the tooth, invested, and, after melting out the wax, solder is flowed into the vacancy, filling completely the space occupied by the wax. The top of the lingual portion will now be thicker than is necessary, but can be easily ground or filed down to the proper thickness. We now have a band which fits all portions of the tooth per- fectly. The anterior end of the bridge is soldered to this band, and after the work is properly finished it is ce- mented in place in the usual manner, b and c, Fig. 277, show side and lingual views of this band after the fitting is completed. " Figs. 278, 279, and 280 illustrate a method of inserting ex- tensive pieces of bridge-work in cases where there are no natural teeth or roots for supporting one end of the bridge. The work from which these drawings were made was constructed by Dr. H. A. Parr, of New York. By this method bridges may • be inserted in cases where all of the teeth on one side of the mouth have been lost, or where all of the teeth anterior to the molars on both sides are wanting. Crowns are first fitted to the teeth which remain. These crowns being in position, an impression is taken. From this a cast is obtained AArith the crowns in their proper positions. A second impression is also taken of that portion of the mouth Avhere there is no natural support for the bridge. From this impression metallic dies and counter-dies are obtained, from Avhich is ' struck' a small gold plate about three-fourths of an inch in length and Avidth, the size of the plate varying according to position and other BRIDGE-WORK. 365 conditions. After this little plate or ' saddle' has been perfectly fitted, it is waxed in the proper position on the model, Avith the crowns. The intervening teeth are now placed in position, and the work invested and soldered. I have had no practical expe- rience with this method, but Dr. Parr informs me that he has Fig. 279. inserted several cases which are being worn with perfect satis- faction. To provide for the possibility of shrinkage or absorption at the point Avhere the plate or saddle rests, I would suggest that it be not soldered to the bridge, but attached by means of an adjustable screw. Fig. 280. " Fig. 281 illustrates another device for obviating the neces- sity for removing the crowns of natural teeth in preparing the mouth for bridge-Avork. Crowns are fitted in the mouth to the points of attachment in the usual manner. An impression is Fig. 281. 366 MECHANICAL DENTISTRY. taken, bringing the crowns away in their proper positions. From this the cast or model is obtained. Heavy bands of half- round gold or platinum bars are now fitted around the necks of the natural teeth on their lingual surfaces. These bands being waxed in position, serve to connect the different parts of the bridge, uniting them in one piece without the loss of any of the natural crowns. I have found this a highly satisfactory method of inserting extensive pieces of the work. Fig. 282 shows the mouth as presented for which the piece shown in Fig. 281 was constructed. Fig. 283 shows the piece in position. "Fig. 284 illustrates a case which is a type of a class of frequent occurrence. Alternate molars and bicuspids in the Fig. 282. upper and lower jaws are lost until the occlusion is some- what changed, and the force of mastication is gradually brought upon the front teeth. Rapid wearing of these teeth results. These cases are among the most difficult that the operator is called upon to treat by the ordinary methods. In the case herewith illustrated, the lower bicuspids with a molar on one side were in good condition, but the loss of the upper bicuspids and molars made them useless. As usually happens, the upper incisors had suffered most. The lower incisors were restored by capping them with cohesive foil. The bridge shown at Fig. 285 was constructed for the right side of the upper jaw, while BRIDGE-WORK. 367 the teeth on the left side were restored by contour work, as shown at Fig. 286. " The superiority of the condition of this patient's mouth, which resulted from this work, over anything Avhich could have been accomplished by plate work, is almost inconceivable to one not familiar with these methods. " The only annoyance which bridge-work is likely to cause patient or operator is the occasional breaking of a porcelain, an accident of not frequent occurrence. While the replacing of a broken porcelain has never been a matter of extreme difficulty, yet I have always regarded the methods hitherto employed as more or less imperfect and uncertain in their results. This led me to devise a method of replacing broken porcelains which leaves the work fully as strong as before; a method Avhich makes the operation a very simple one, requiring less than an hour for its performance; and after the porcelain has been re- placed, an expert would r A ,. r r Fig. 283. not discover any traces of an accident. After remov- ing all traces of the broken porcelain, the projecting pins are cut off, and tAvo holes drilled through the backing in the exact posi- tion occupied by the pins. The narroAv space of metal now intervening betAveen these two holes is cut out Avith a fissure-bur. This leaves a groove which should not be wider than the diameter of the pins. The length of this groove should now be increased on the lingual surface, but not on the front. The object of this is to give a dove-tail shape to the groove, which is easily effected by the use of the same fissure-bur above referred to. The lin- gual appearance of this groove when properly shaped is shown in Fig. 2.S7. The proper tooth is selected, the pins passed through this hole and bent outward into the dove-tail groove. It will be found almost impossible to bend these pins into their proper positions by any ordinary means, so as to hold the tooth 368 MECHANICAL DENTISTRY. quite rigid and immovable. An instrument herewith illustrated (Fig. 288) accomplishes this feature of the work in a very sim- ple and effective manner. Its use is almost too nearly evident to require description. Both the rubber pad Avhich rests upon the porcelain front and the wedge-shaped point Avhich passes Fig. 284. Fig. 285. between the pins are made to rotate in their sockets, so that any desired position can be obtained. A firm closure of the instru- ment when in position forces the pins outward into the dove- tail groove, and the tooth is immovably fixed in place. It now remains but to fill the space between the pins with any form of Fig. 286. Fig. 287. cohesive gold (I use crystal gold), and with corundum, Arkan- sas, and rubber points in the engine the surface is finished and polished. The wedge-shaped filling of crystal gold acts as a keystone between the pins, and makes a most perfect method of repair. BRIDGE-WORK. 369 " The practice of extracting badly-decayed and broken-down teeth, particularly when they become a source of constant an- noyance, and replacing them with artificial substitutes mounted upon rubber, celluloid, or metallic plates, has become so firmly established in the public and professional mind as the proper and unavoidable thing, that the folly of such practice can only be demonstrated by persistent and long-continued endeavor. The statement, therefore, that it is no less a criminal practice, in principle if not in degree, to extract a tooth because it is in an ulcerated or broken-down condition, than would be that of amputating a finger because of the appearance of a felon, or removing an eye to get rid of a cataract, will seem a radical one. But if my experience has taught me anything, it certainly is no exaggeration of fact. Diseases of the teeth and the sur- Fig. 288. rounding tissues are certainly as amenable to treatment as are ulcers or morbid growths in other parts of the body. The only conditions necessary to the successful accomplishment of this are requisite knoAvledge and skill in the operator and a desire on the part of the patient to have a healthy mouth. "A properly made artificial crown mounted upon a root, the investing membrane of which is in a healthy condition, is quite as useful and, all points considered, perhaps quite as desirable, as a pulpless tooth with its natural crown intact. Such is my confidence in the intrinsic merit of bridge-work that I think it requires no very great degree of foresight to predict that the day is not far distant Avhen a large per cent, of the now prevalent partial-plate wrork will be a thing of the past." 24 370 MECHANICAL DENTISTRY. The following is a revised account, illustrated Avith new and original cuts, descriptive of Dr. J. E. Low's more recent methods of procedure in the cases under consideration, a method of replacement to Avhich he has been long and successfully devoted. The author is indebted to Dr. Loav for their special preparation for this edition. The writer's definition of " bridge-Avork " has special application to his distinctive method of construction. He says:— " Bridge-work consists in supplying vacancies between teeth or roots with artificial teeth, attached to the adjoining natural teeth or roots by means of bands or crowns, and held in such a position, that there is no contact with or pressure on the gums Fig. 289. beneath, and thus no opportunity for secretions or other foreign matter to be held there, and thereby become offensive. " There is really but one kind of bridge-work, and but one way to make bridge-work to insure success. There are many ways of making teeth without plate, but this is not bridge-work. I will here try to explain in detail my manner of making and adjusting bridge-work. " For the first illustration, as seen in Fig. 280, we have a case Avhere all the teeth have been extracted, except the twTo cuspids, and tAvo second molar roots. " Yxe first proceed to prepare the roots by crowning. I use BRIDGE-WORK. 371 gold crowns on the molar teeth, and what is known as the Low crown on the cuspids. The preparation of the two cuspids consists in making the crown ready for adjustment, the pro- cess of which is described in detail in another part of this work. I always measure the tooth to be crowned with gold, with a strip of block tin, No. 35 thick Stub gauge or there- abouts. Place the tin around the tooth and with pliers carefully measure the full size of the same. " Should you be measuring a tooth, or part of a tooth, on which there are projections, take the engine, and with a stone grind off the same, making a smooth surface, so there will be nothing to interfere Avith the fitting of the bands properly. After cutting the tin measures by the marks made by the pliers, you have the measures ready to make the gold bands by. Cut the bands and bevel the edges and solder together, and you are ready to fit. After fitting all the bands, and finishing the crowns in the usual way, I place each in position in the mouth, having previously regulated the articulation of each crown as desired, in the process of making. We now take a deep articulation in wTax, and impression in plaster-of- Paris; remove before it gets too hard, and place all the crowns in their positions in the impression; varnish, oil and pour in the usual Avay; separate the cast from the impression and place in the articulator. Then pour with plaster. After the plaster has hardened, remove the wax, and wTe have the articu- lation proper, and are ready to select and grind our teeth, having previously selected our shade. My experience has long ago taught me that no porcelain tooth can stand the pressure for bridge-work, the strain on them being twice as great as Avith teeth on plates, Avhich rest on the gums that give to pressure. In order to prevent breakage of teeth and give strength, I have for many years been making a tooth with gold cusps. I will here describe my manner of doing so. " For the first step, I use No. 28 gauge platinum for a cover- ing of the inside of the tooth, or just where you wish gold to flow. Then I bend the pins doAvn to hold the platinum in position, and with a file remove all overlapping platinum to prevent breaking of our tooth in heating. The tooth is made 372 MECHANICAL DENTISTRY. flat on the crown surface with the express intention of restoring with a gold crown. This crown need not be very thick, but should perfectly resemble the cusps on the natural tooth, for the purpose of mastication. As these cusps are not on the market, and every dentist making bridge-work cannot make it in a way to stand, without putting gold cusps on the grinding surface of the bicuspids and molars, I will here describe, for the benefit of those who do not know how to make them, how they can be made with very little trouble. Pick out a natural tooth with cusps, the exact shape you wish to have your gold cusps resem- ble ; mix up some fire clay in a thick paste; then press your tooth into it a little deeper than you wish the cusps. Having made the proper impression, remove the tooth, and set the im- pression over the gas stove to dry. After it is dried and reason- ably hot, lay your pieces of gold in the impression and with a blowpipe melt them. When melted, press with a piece of steel on the gold till cool. This mold will do to make many from. If you have not the fire clay, and can get charcoal that is burned from fine grained wood and is soft, you can simply press your tooth into the charcoal and melt in the same way, or you can carve your teeth as you desire in a block of carbon. Of course, the little steel dies are handier, as we can swedge up our gold cusps in them, either solid or thin. " Having described our manner of making the cusps, we will now return to the manner of finishing our tooth. YTe left off by saying we covered the inside and bent down the pins and filed off the overlapping platinum. We now place our cusp on the top of the tooth, and place in the position desired, hold- ing it there with wax, and with a spatula trim the wax the exact shape we wish our tooth to be, V-shape, tapering from the crown down. We now encase in plaster and sand, which gives us a box. When hard, remove the wax and place over the stove, and when sufficiently dry, fill in with coin-gold, using the blowpipe to melt it in a solid mass, and our tooth is ready to file up and place in position on the articulator. Fig. 290 shows the tooth in this condition. "After our teeth are arranged, we hold the same in position with wax, remove from the articulator, encase with plaster and BRIDGE-WORK. 373 sand or asbestos in the usual way. That we may Fig. 290. have a strong case, I always use platinum wire between each tooth, and then proceed to heat and solder. Be sure that all the gold cusps are so arranged that you can get all soldered together, as this gives us great strength. My formula for solder, which I have used for many years, and Fig. 291. Avhich will be found very easy-floAAnng, and almost the exact color of the gold you are using, is as follows: Ahvays figure from the carat of gold you are working. Take 1 pAvt, coin- gold, 2 grains of copper and 4 of silver. YTe noAv have our case soldered; after filling as desired, commence to finish AATith felt wheels and pumice stone, after which we use rouge buff Fig. 292. wheels. Yre are now ready to adjust in the mouth. In Fig. 291 Ave see the case ready for adjustment. " HaA'e the assistant dry all the teeth or roots to be operated upon Avhile you are mixing the cement. Be sure and use a kind Avhich does not harden very rapidly, or your cement will set before you get your teeth adjusted. Use sufficient cement 374 MECHANICAL DENTISTRY. to fill all the gold crowns perfectly when the case is driven to place. Moisten the step-plugs and cap with cement, touching every portion, and with an instrument place a little cement in the bottom of the cavity. We now adjust our case, using the little roter for the Low crowns, and a piece of ivory for driving on the gold crowns. Fig. 292 represents the case when in position. " It will be seen by looking at the previous cut (Fig. 291), that the teeth, after having been soldered, are all spaced fully one- third of the distance from the place of contact Avith the gums and the grinding surface of the teeth, so that secretions could not possibly lodge there. I have given a description of my manner of making a full upper case of bridge-work Avhere there are roots to be crowned to support the bridge. I will now describe my manner of operating upon a case where the four centrals are missing. As seen in Fig. 293, to supply these four teeth where the cuspids are intact, I use a gold band. " I first measure the tooth with strips of tin, and make the gold bands, as before described; cut out the out- side lower portion of the band before beginning to fit. In fitting, as the band | is being driven down, cut away any of the band that touches the gum before all touches: never drive the band under the gum, as in- flammation would proba- bly follow. " I mention this, as I have seen many attempts to get rid of the band by driving up under the gums and cutting them out on the front, until they were too narrow for strength. It is hard work to make something out of nothing. The bands should be heavy and strong, and the patient made to understand that if he expects to get rid of the annoyance of the plate, he must sacrifice his dislike to showing gold. After driving the bands up close to the margin of the gums, as the cuspid teeth are very BRIDGE-AVORK. 375 tapering, the bands will have to be taken in at the bottom. To do this, I slit the band about a third of its length up, then place it on the tooth again, lap it over enough to bring it to a close fit, and then take it off and solder. " Continue taking it in wherever it does not perfectly fit the tooth, and after a good fit is obtained proceed as before described, by taking an articulation and impression. In adjusting, first try the case on to see that it fits, and that the articulation'is all right. Next have the assistant dry the teeth upon which the bands are going, and then mix your cement. This should be mixed to about the consistency of thick cream. It must be neither too thick nor too thin, or the adhesion will not be strong enough to hold. Cover your teeth with cement and then the inside of the bands. Place these on the teeth and carefully mallet to position. For this purpose I use a steel instrument, with a crease or groove in the end. The teeth must be kept dry, after the case is in position, until the cement is well set. After this is done, bevel the edges of the bands and burnish close to the teeth, and if burnished properly they will be made to resemble gold fillings. Fig. 294 represents the case com- pleted. " I am aware that, in a case like this, porcelain croAvns instead of gold bands could be used, and I should consider it much preferable to do so where Ave have roots or unsound teeth to operate upon, but do not advise the destroy- ing of nerves, where the teeth are intact, to supply such a case with crowms, as the bands will answer every purpose for many years. " If they should give out in after years, the roots can then be crowned. I have many of these cases that have been in use eight and nine years, some of Avhich have never loosened, and some I have reset nearly every year. I always impress upon the Fig. 294. 376 MECHANICAL DENTISTRY. patient the necessity of having them reset immediately should they become loose, and advise them to have their cases exam- ined at least once a year. Should parties insist upon having crowns used to supply a case, like the one just described, on per- fectly sound teeth, I should begin by using an aluminum disk, with corundum, cutting deep as possible, both on the labial and lingual sides. Then use the excising forceps. This can be done under the influence of an anaesthetic, or otherwise. It is not by any means so painful an operation as one would think. If the nerve does not come out with the piece of tooth cut off, I take a piece of orange wood, which I have previously cut the proper shape, to drive into the nerve canal. I place it in creo- sote, and let it soak a few minutes before beginning to operate. Fig. 295. I immediately, after severing the tooth, drive this into the canal, then remove, and dip in creosote and drive in again. This will perfectly fill the nerve canal; all sensitiveness will disappear, and you can begin to operate at once. I do not recommend this treatment for sound teeth, but I have treated many ex- posed nerves in this way; also, many teeth broken by accident, and think this the most satisfactory way to dispose of such cases. I have never had any unfavorable results follow after operat- ing upon teeth in this way, and I can hardly say as much in favor of any other treatment. I speak of this manner of treat- ing exposed nerves as one of the operations that sometimes becomes necessary in adjusting a bridge properly. I do not BRIDGE-WT0RK. 377 claim any originality in this mode of treatment. I know several dentists who use this method, all of whom report satis- factory results. We now have the roots prepared to receive the case as shown in Fig. 295. " I have many of these cases in use that are giving entire satisfaction. The instrument selected for preparing these roots Fig. 296. Fig. 297. should be one with small inside cutters and large bevelers, so as not to cut away any more tooth-substance than necessary. " Fig. 296 shows the case ready for adjustment, and Fig. 297 represents the case after adjustment. " In this article I have described my manner of making teeth for bridge-work. I am now having made a tooth ex- pressly for bridge-work which I hope to be able to place on the Fig. 298. Fig. 299. Fig. 300. Fig. 301. Fig. 302. Fig. 303. market soon. I have been using them, but have not perfected my shells and molds sufficiently to enable me to get them out in large quantities. " Fig. 208 shows us the sockets, which I propose to have ready made in various sizes in bicuspids and molars. " Figs. 299 and 300 represent the shells, Avhich are to be 378 MECHANICAL DENTISTRY. placed in their positions after the case is completed and ready for adjustment. " Fig. 301 represents the sockets as made for the four central and two cuspid teeth. The advantage of these teeth can readily be seen, not only for bridge-work, but all gold plates. A tooth if broken can readily be replaced Avithout removing the bridge or cracking by soldering, and at small expense. " Figs. 302 and 303 represent the teeth placed in position." Dr. James E. Dexter, in a paper read before the First Dis- trict Dental Society of New York, June, 1883, exhibited models and submitted descriptions of an appliance which he denomi- nates the " Cap Plate," which is removable from the mouth. This mode of substitution, which it has been claimed was tried in England twenty years ago, and abandoned as injurious to the teeth capped, is intended to obviate the objections Avhich Dr. Dexter strenuously asserts attach to the ordinary forms of bridge-work permanently fixed in the mouth. Space Avill admit of only such parts of the paper as relate to the mechan- ical construction of the appliance. " Leaving now bridge-work, let me speak of cases in which AAre could (and often do) wish for some method of inserting artificial substitutes other than ordinary plate-work. Take a case where, on the lower jaw, there are standing in the mouth a third molar, a canine, and first bicuspid, on each side—six teeth in all. These teeth are shortened, by breakage and mas- tication, so that the upper incisors close to within an eighth of an inch of the gum line between the canines; added to this, they are so tipped and twisted in their places as to make it very difficult to properly adapt an ordinary denture to the spaces between them; and, lastly, let the patient evince entire abhorrence of, and a fixed resolution not to permit, the resting or pressure of any appliance upon his gum tissue. Such a case is the one for which I have constructed this cap-plate. Such cases are often treated by building up or down the natural teeth with gold, in order to open the bite, and then replacing lost teeth with an ordinary plate. My apparatus, however, accomplishes both these desiderata in one operation, while simultaneously avoiding any and all pressure upon or irritation of the gum. BRIDGE-WORK. 379 " The appliance which I iioav show you (Fig. 304), is constructed as folloAVs: Caps of gold-ana- platinum alloy, of about Nos. 26 to 28 U.S. standard gauge, are struck up to fit over and doAvn the sides of the nat- ural teeth selected for the piers, fitting closely. If all the supporting teeth stand perpendicularly and paral- lel with each other, thus creating no ' undercut' (so to say), the sides of the caps may encircle the teeth as far as possible, (not, hoAvever, imping- ing upon the gum line), and be simply slit (in two or more places on each tooth) perpendicularly, so as to spring apart and alloAv of sliding the whole over the natural convexities of the teeth, the sides coming together again Avhen in place, and thus holding the Avhole apparatus firmly. But should the teeth be tipped or leaning, and not parallel, the sides of the caps must then extend over only such parts as can be closely fitted, and yet be sufficiently perpendicular and parallel, to allow of re- moval and replacing of the appliance. Of such a character is the case now shown you, there being only one place on the six caps Avhere a slit is of value; the sides of the caps being so fit- ted as to hold partly by their own elasticity, and partly by that of the Avhole apparatus. Such a case, of course, will most severely try the capabilities of any artificial denture; and not the least merit of the present piece is its triumph over, and per- fect and practical adaptation to, the obstacles of an exceptionally difficult case. " The caps, when struck up, will not cling to the teeth Avhen in place; nor should they, for they must be capable of easy remoAral during succeeding processes. But Avhen the piece is ready for final insertion, the sides of the caps must be sprung inward sufficiently to hold their supports with firmness. " The caps being now made, it is in order to determine the length of ' bite' needed. Place the caps in position in the 380 MECHANICAL DENTISTRY. mouth, and build wax on their grinding surfaces to a proper length and contour, both side and grinding. Invest, remove wax, and flow into its place eighteen-carat gold. Shape the grinding surfaces, by trial in an articulator or the mouth, to the proper occlusion. Next, take an impression with the caps in place, pour the model, select and back plain plate-teeth, and wax them in place. Invest the whole, remove the wax from the backs of the teeth, and fit in the spaces between the caps, bands, or bars of irido-platinum alloy (or gold, as circumstances may determine), being careful that the bars fit accurately to the back- ings of the porcelain teeth, and to the caps at each end. In fit- ting the bars to the caps, select such points of attachment as will not interfere with the spring of the slit sides of the caps. If necessary, let the bars avoid the sides of the caps, and reach, by curving, to the tops or grinding surfaces. Should you desire to arrange the porcelain teeth irregularly, you need not hesitate to do so. Set them just as you would for rubber or celluloid, and then, simply taking a 'finger impression' of their backs with modeling composition or wax, when invested as above stated, and making dies, you can readily ' strike up' your bars to fit the irregular positions of the backings. But should this be difficult, on account of great irregularity, or stiffness of bars, then construct the bars of two or three thicknesses of metal, each struck up separately, and then ' sweated' into one. Next, solder the bars to the backed teeth, but not to the caps, as yet. The reason is that perfect adaptation of the bars to the caps is absolutely necessary to the success of the piece. Therefore, now place the caps in place in the mouth, and wax the bars with their attached teeth in the spaces between them; filing, grind- ing, and adjusting until all is exactly as required. Then (and not until then) take an impression of the Avhole in place, the apparatus coming away with the plaster. Pour the impression with plaster and pumice, sand, or asbestos (sand is best), care- fully remove the impression plaster, invest outside the model with its sustained apparatus, and then solder the caps and bars together. In doing this, as little solder as possible should be used, to prevent warping of the whole. The bars should have a broad, firm hold on the caps; but the contour of their union BRIDGE-WORK. 381 should be made on the bars before they are united to the caps, and not by floAving on a body of gold Avhile uniting the bars and caps sufficient to attain the desired hold and shape of union. On the contrary, the bars should be properly shaped at their ends, and carefully fitted to the surfaces to which they will be attached, when a small amount of solder flowed into the joint will make a perfect union and give all the strength possi- ble. This is not plumbing work. All that now remains to do is to spring or bend slightly inward, as before directed, the sides of the caps so that they may grasp their supporting teeth firmly, yet not too much so to create difficulty in removal or insertion; then finish and polish. Burnishing is generally objectionable, since it gives, in some lights, a black shine to the piece, adding greatly to the prominence of the appliance as a part of the vieAv, whenever the wearer opens his mouth. " Should it be desired to produce the best possible results with the piece, the interstices between the artificial teeth and any other crevices to be found may be filled Avith gold or amalgam—I prefer the former; or vulcanite may be packed in such places (which may be, if necessary, cut out to proper di- mensions by buring), and finished up smoothly. The piece shown you contains no less than seventeen gold fillings, which signifies that no debris, or even moisture, has any foothold of concealment about it, and that it is, therefore, as clean in itself as is possible for any artificial denture to be. This, you will say, is rather expensive work. Yery true. The whole method is expensive in both money and labor. But I am quite consoled for this fact by the thought that it will not, therefore, be likely to do much harm to the public, since the 'cheap-jacks' and 'in- competents' will probably let it alone. " In the piece shown there are six caps, three on a side. There are five incisor teeth placed between the canines, two of which are capped with gold to break up the uniformity of por- celain in front, as contrasted with the uniformity of gold behind, and thus help to evade artificiality of appearance. Between the molar caps and the double caps for canine and bicuspid, the connecting bar is horizontally placed, dipping downward to parallel the gum line, as well as to evade an encroaching 382 MECHANICAL DENTISTRY. molar above. YThen necessary, an artificial tooth or teeth can be ground and soldered to these bars. Generally, however, the connecting bars should be perpendicularly placed, to insure resisting strength in the line of the attacking force. " Ararious modifications of this process, as regards its uses, will at once suggest themselves. For instance, where a molar or tAvo on one side are missing, they may be thus artificially replaced without a plate, provided there is a supporting tooth or teeth at each end of the space; or the method may be ap- plied to the treatment of irregularity by capping the molars and bicuspids, or molars alone, connecting the caps of each side together, if necessary, by a band or strap directly across the roof of the mouth, or curving around back of the incisors. To these bands or straps, or to the caps themselves, hooks or but- tons for attachment of loops, strings, etc., or threaded nuts for use Avith screws may be soldered. Should it be desired, for instance, to ' spread' the bicuspid region, place on each pair of these teeth a cap having a socket formed on its inner aspect, and let the ends of a ' Coffin' steel spring rest in these sockets, the force of the spring retaining it in place, and the teeth alone being forced apart without pressure on the gums. This is appli- cable to a single tooth by making the opposite cap enclose teeth enough to resist back pressure. A large proportion of the gum- irritation usual with treatment of irregularity may be avoided by use of the cap-plate instead of ordinary plates. " Should it be desired to use the cap-plate where it is not ad- visable to open the bite, the caps may be struck and fitted as before directed, and then be cut through and away only at the points of occlusion, leaving the balance as before. In doing this, however, be sure to leave enough grinding surface to the caps to securely fasten the spring-sides together. " This method is eminently applicable to cases where roots only remain in the mouth—provided they are sufficient in number and strength to sustain mastication. The variation of the process here required is simple. Pivot or ferrule perma- nently the roots by any proper process (the Biittner method is the best in this case, because the strongest); but, instead of mount- ing porcelain teeth on the pivots or ferrules, fit thereon gold piers BRIDGE-WORK. 383 or stumps of a proper shape (parallel-sided) to receive the caps; and Avhen all the roots are so mounted, proceed exactly as though the metal piers were so many natural teeth,—capping them as such (letting the caps assume the form and size of teeth), and fitting connecting bars and porcelain teeth into the interspaces. Root-cases should be exceptionally favorable ones for this method, since the piers can be placed exactly perpen- dicular to each other, and be so shaped as to secure for the caps the best of anchorage and bearing." The latest device in the way of removable bridge-work, con- FlG. 305. trived by Dr. R. Yralter Starr, of Philadelphia, Pa., and copied from the January (1886) number of the Dental Cosmos, is thus described:— "The case of Mr. W. presented difficulties of an unusual character, as may be seen by inspecting the illustration, Fig. 305, which renders detailed description unnecessary. "It Avill be observed that the molars and the left second bicuspid overhang to a degree that would make the taking of an accurate impression by ordinary methods well-nigh impos- sible. After a careful study of the case, it Avas decided that two 384 MECHANICAL DENTISTRY. separate pieces of removable bridge-work should be attempted, and, as an essential preliminary step, the overhanging sides of the molars and bicuspids were ground with engine corundum wheels and points until those sides were made much less in- clined, when plaster impressions were taken, first of one-half, and then of the other half, of the jaw. Gold cap crowns were closely fitted over the molars, left second bicuspid, right first bicuspid, and cuspid stump. Gold crowns were made to tele- scope over all the caps, which were then, by means of oxyphos- FlG. 306 phate cement, fixed firmly on the teeth. Suitable plate-teeth were selected, fitted, backed, and hard-waxed in place between the telescoping crowns. After hardening the wax with cold water from a tooth-syringe, the pieces were carefully removed, invested, and soldered. The tAvo completed bridges were easily replaced on or removed from the supporting capped teeth, and their appearance when detached is correctly shown by the illus- tration, Fig. 306, which also shows the capped teeth and stumps. BRIDGE-AVORK. 385 This figure likewise shows the results of the novel method em- ployed in crowning the incisors. Gold collars were fitted tight on the necks of the incisor stumps, and the new-style porcelain caps adjusted in the collars, and set in the oxyphosphate cement which had been packed into the collars; thus at the same time fastening the collars on the stumps and the caps in the collars, as shown completed in Figs. 306 and 307. " Fig. 307 illustrates the finished crowns and bridges, which latter were secured in position by placing a small piece of gutta- percha in each of the telescoping cap-crowns, which were then Fig. 307. warmed and carefully pressed in place—the gutta-percha filling only the spaces between the flat tops of the caps of the natural teeth and cuspid caps of the bridges. " Whenever, for repair or for any other purpose, it shall become desirable to remove one of the bridges, that may readily be done by applying a hot instrument or hot air to the caps to soften the gutta-percha sufficiently to permit the telescoping bridge to be taken off. "A full upper vulcanite denture Avas made to replace the old one, Avhich, by improper occlusion, had thrown the full force of 25 386 MECHANICAL DENTISTRY. mastication on the anterior teeth of the lower jaw, and produced the destructive action that resulted in the deplorable loss of tooth-substance shown in Fig. 305. " The prosthetic devices thus briefly described have so far proved perfectly satisfactory to both patient and dentist. The obvious difficulties of the case, and the somewhat novel means employed in supplying useful and secure dental substitutes, seem to justify the writer in bringing the case to the attention of the profession." The author is indebted to the S. S. YThite Dental Manu- facturing Co. for proof-sheets descriptive of methods of Bridge- Yrork, in which the " Seamless Collar " is conspicuously em- ployed as a means of permanent attachment; also some account of original methods of constructing removable appliances of the same character. A number of the illustrations accompanying the following extracts from this paper, which is entitled, "A System of Crown- and Bridge-Work," have already been incorporated in the text in connection with Dr. How's processes relating to the construc- tion of " Seamless Collars," to Avhich the reader's attention is directed by appropriate references. After considering the several devices used in such processes, the paper adds:— " To illustrate the uses of these appliances take a case in which the two inferior bicuspids of the left side are missing, and the croAvns of the cuspid and first molar so badly decayed that the probabilities are that they Avill soon fall victims to the forceps. The old-time way would have been to extract the molar and cuspids, and make a partial plate. Examination, hoAvever, shows that the roots of these two teeth are in good condition, affording an excellent opportunity for the construction of a piece of bridge-work. " Yrith a corundum point or rotary file, cut off the remaining portions of the crowns level Avith the gum margins. Prepare the roots in any of the well-known ways, thoroughly cleansing the apical portions and filling them with whatever material is desired, being careful only that the work is well done. For the better retention of the filling material to be placed in the pulp- chamber, retaining-grooves can be made or retaining-posts in- BRIDGE-WORK. 387 serted. Take a piece of binding-wire (No. 26, American gauge), say 1\ inches long, pass it around the neck of the molar stump, cross the free ends, and, holding the wire in place with one finger, twist the ends with a pair of flat-nose pliers until the wire clasps the tooth closely at every point (Fig. 156). Where there are any irregularities in the contour of the tooth, it is necessary to press the wire into them with an approximal bur- nisher. It is obvious that the ring thus formed will show the exact size and shape of the neck of the tooth. Remove the ring carefully, lay it on the lead anvil, put over it a piece of flat metal, and with a smart blow from a hammer drive the wire into the lead (Fig. 157). Upon removing the wire an exact impression of the ring will be left in the lead anvil. (This part of the work, as indeed all others, should be done carefully as described. The wire ring may be driven into the lead by a direct blow of the hammer face, but the blow might not strike equally, and the interposition of the flat metal held level insures an even impression. A piece of an old file is best, as the file- cuts keep the wire from slipping.) " Next, cut the wire ring at the lap, straighten out the wire, and select a suitable collar by comparing the length of the wire with the straight lines in the diagram,* which show the inside diameters of the various sizes. Should none of these correspond exactly take preferably the next size smaller. It will be remem- bered that the collars are No. 30 in thickness, while the wire with which the conformation is secured is No. 26. This differ- ence permits the collar when contoured to shape to enter the lead impression readily, a decided advantage in fitting. Having selected the collar, fit it to mandrel No. 5,f with the peen of the hammer, holding it upon the lead anvil, and using a slight pushing force to help in stretching and forming it (Fig. 158). Having driven the collar to form, remove it from the mandrel and try in the lead impression. If it does not fit exactly return it to the mandrel and stretch it a little, when it will usually fit perfectly, as the mandrels have been designed carefully to the * See advertising columns of Dental Cosmos. f Mandrels of various sizes are represented in advertising columns of Dental Cosmos. 388 MECHANICAL DENTISTRY. average shapes which obtain in the great majority of tooth- necks. In the exceptional cases where the collar does not fit it can be readily contoured to the exact shape with a pair of flat- nose pliers. Of course, if it fits the impression in the lead, it will fit the neck of the tooth, always provided the measurement and the impression have been carefully made. " If the collar or band has been accidentally stretched too much, or if* for any reason, when brought to shape, it is too large, its root end can easily be reduced to the proper size by Fig. 308. Fig. 311. the use of the contractor. Place the edge of the collar which is to fit the root in the proper hole; hold it level with a piece of file as in taking the lead impression of the ring, and tapping lightly on the file drive the collar into the plate (Fig. 161) until the proper reduction is made. The collar is next' festooned' to correspond to the shape of the maxillary ridge. Lay it, gum edge up, on the lead anvil and with the piece of flat file and the hammer drive it into the lead. A few cuts with a fine half-round file across the approximal diameter will conform BRIDGE-WORK. 389 the edges to the surface of the ridge (Fig. 308). Then place the collar in position, and, having ascertained just how far it should go down on the root, remove it, and with the small spring punch in the collar pliers (Fig. 164) form projections on the inside of the band at the proper points to serve as stops which, resting on the top of the root, will prevent the collar from being forced further down upon it than is desirable (Fig. 165). "A collar for the cuspid is then fitted in the same manner, using mandrel No. 6 for shaping, after which the case is ready for the building of the bridge. " Place both collars in position and take an impression of the parts, including the interiors of the excavated pulp-chambers, from Avhich make a cast in the usual way. Bend a short piece of half-round gold or platinum wire into the form of a horse- Fig. 313. shoe, the tAvo extremities of which shall fit into the roots of the molar. Then take a longer piece of the same wire, somewhat more than enough to extend from the toe of the horseshoe when in position to the cuspid root; bend one end of it at a right angle, or nearly so, to fit the root of the cuspid, and (cutting off any excess of length) solder the other end to the toe of the horseshoe. The bar extending between the two roots is the truss of the bridge. Next, place the appliance on the cast (Fig. 311), holding it in position with wax, and select the teeth to take the place of the missing bicuspids and molar. The best form for this purpose is a tooth having holes extend- ing through it vertically from the neck to the grinding surface similar to the well-known Bonwill Crown. 390 MECHANICAL DENTISTRY. " The crowns used should be large enough to fill the space rather tightly, even if their sides have to be flattened slightly to let them in. If the teeth do not fill the space tightly, a small portion of plastic filling material crowded betAveen them, as mortar between the granite blocks in the arch of a railway bridge, will greatly increase the strength of the work. "After the teeth are ground to fit and the proper length for occlusion ascertained, the truss is covered with a thin film of wax, upon which the crowns are again pressed to their positions. Upon the removal of the crowns the impression of the holes running through them will be found in the wax. At these points drill holes through the bar with a small twist-drill run by the engine, and into these fit and solder the pins for the support of the crowns. Fig. 314. " The bridge is now ready to be attached permanently. Set the crowns in position upon their supporting pins to secure the proper alignment. (If the operation were upon the upper jaw they would have to be held with wax.) Put into the canals of the supporting roots (the cuspid and first molar) a sufficient quantity of some quick-setting plastic, as oxyphosphate, to about half-fill the pulp-chamber, but not enough to prevent the supports of the truss from being forced home. Force the bridge supports to place, and after allowing the filling material to become set remove the crowns. Fill the remainder of the pulp-chamber and the whole of the collar with gold or with amalgam, gutta-percha, oxyphosphate, or any suitable plastic (Fig. 312). Set the crowns permanently, the molar and cuspid first, as this affords greater facility for the trimming off of any BRIDGE-WORK. 391 excess of the filling material used in the attachment. For attachment of the crowns, gutta-percha is probably the best material, as crowns set with it are readily removed for the cor- rection of any inaccuracies of occlusion or alignment, by grasp- ing them betAveen the beaks, previously warmed, of a pair of universal lower molar forceps. The heat warms the gutta-per- cha and releases the tooth, which can then be reset properly. In attaching crowns with gutta-percha the holes in the crowns are first filled with the material, after which the crown is warmed and forced to place. Any of the other plastics ordi- narily used in setting BonAvill Crowns can be employed, at the discretion of the operator. Fig. 314 shows the case completed. " In securing the occlusion of a piece of bridge-work it is well to make the artificial teeth a little short, so that the natural teeth on both sides will meet the first shock of mas- tication. Nature will correct the occlusion in time by slightly elongating the roots supporting the bridge. If the artificial crowns are permitted to strike the natural teeth from the first, the undue strain upon the two supporting roots will cause soreness and, perhaps, more serious consequences. " When a sound tooth is to be used as one of the supports of the bridge, a modification of the method just described is neces- sary. Take a case where it is desired to bridge the space caused by the loss of the right inferior bicuspids and first molar. The croAvn of the right cuspid is nearly gone, but the root is sound and capable of supporting one end of the bridge. The other end will be attached to the second molar, which is a sound tooth. Prepare and band the cuspid root as before, dress off the second molar crown until it is slightly smaller than the neck, so as to permit a cap to be telescoped over it, and take the measure of the crown with the binding wire. Select a Suitable seamless collar of sufficient Avidth to extend from the neck to a little beyond the grinding surface and drive it up on the proper mandrel to get the general shape, but not the full size re- quired to fit the tooth, leaving it so that the edge having the larger circumference Avill just pass over the end of the crown ; place the collar on the tooth and Avith a block of wood and the mallet tap it to place just beyond the free margin of the gum. 392 MECHANICAL DENTISTRY. This method will make a close fit, as the collar will readily stretch all that is necessary. YTith a sharp-pointed instrument mark the length of the crown, remove the collar, and cut it to the proper width as indicated. Then in a piece of gold plate of the thickness used for caps form four little depressions of the general character of an impression of the molar cusps. An easy way to do this is to lay the plate on the lead anvil; then with the ball on the end of an ordinary socket-handle and the ham- mer the depressions are made in a moment. Set the collar on the plate, borax it, charge Avith solder, and heat till the solder flows. Cut off %the surplus plate and a perfect cap for the molar is made. Place it on the tooth and take an impression, and thereafter proceed as before directed to make the truss of the bridge and mount the teeth, except that in this case the poste- rior end of the truss is to be soldered to the molar cap. For the final attachment place a little oxyphosphate or any other plastic filling material in the cap to secure it firmly (Fig. 314), first cutting a slot in the crown end for the escape of the excess of material. Pressure upon the filling material hastens its hard- ening. " Detachable Bridge- Work.—A description of Iavo or three methods of constructing detachable bridges "will suffice to in- dicate the general principles involved. Having these, each operator will find it an easy task to devise the modifications necessary to adapt a method to individual cases. " The first method is especially applicable to cases Avhere both ends of the bridge are attached to roots, as, for example, the inferior cuspid and second molar roots of the left side, the inter- vening teeth having been lost. The operation is conducted as described in the first case of fixed bridge-work down to the con- struction of the truss, for which in this method square gold wdre is used. Having cut the wire of the proper length, lay it upon a piece of gold plate (about No. 20, American gauge) of the same length and full three times as wide, and, placing the tAvo upon the lead anvil, with a hammer and the piece of file be- fore used drive them into the lead. This will form the plate into Avhat we may call an open trunk Avhich fits «the square Avire. Remove the two from the lead together and, without BRIDGE-AVORK. 393 separating them, curve to the proper shape to form the truss. Grind crowns having vertical holes, like the Bonwill, to fit, and having determined the proper points for the supporting pins (see page 394), drill through both trunk and bar at these points. Separate the bar from the trunk and fit and solder pins to the bar. Construct small tubes to fit the pins, ream out the holes through the trunk to admit them, and set the tubes with solder in the enlarged holes (Fig. 315). Fix the crowns permanently upon the tubes. They may be mounted in any of the approved ways, by Amlcanizing or by the use of a plastic filling material. When they are firmly set, place the trunk with the teeth upon the bar and anchor it permanently as already described. Fig. 316 sIioavs the completed work. " In this method the truss consists of the bar and the open trunk Avhich covers three sides of it. The bar is, of course, permanently attached to the roots of the molar and cuspid, but the trunk Avith the teeth can be removed at any time. "The second method of constructing a detachable bridge is applicable to cases Avhere FlG ^w. one or both of the sup- ports or piers are sound teeth. In the case ad- duced for illustration, the right inferior cuspid crown Avas decayed, and both of the bicuspids and the first molar Avere ab- sent. The supports for the bridge Avere the sound second molar and the cus- pid root. After the cuspid root Avas prepared and banded, the croAvn of the molar was reduced very slightly, not sufficient to destroy the enamel, but just enough to permit a collar properly fitted to pass OATer it. A collar someAvhat Avider than the length of the crown from grinding surface to neck was fitted and cut to the proper Avidth. Tavo lugs were then soldered upon the anterior and posterior sides and bent to fit into the approximal 394 MECHANICAL DENTISTRY. fissures, which were slightly cut out to admit them. An impres- sion was taken, the collar Via 31fi . ., , coming away in the plas- ter, and a cast was made with the collar in position. A coned tube was then made for the root of the cuspid and a coned pin fitted into it. A truss of half-round wire was made to which the collar coned pin and the molar were soldered (Fig. 317). A half-clasp to grasp the lateral was next soldered to the end of the truss to be supported by the cuspid. The object of this clasp was to guard against the teeth being thrown out of proper alignment by the force of mastica- tion. BonAArill crowns were then vulcanized to the truss, after their supporting pins had been fitted and soldered to it. (Counter- sunk crowns can be used as well in the same way. Plain plate teeth may also be used in this style of work, in which event they are to be soldered to the truss.) The bridge was then ready to be set, which was accomplished in the following man- ner : The cuspid root was nearly filled with oxyphosphate, and the coned tube was placed upon the pin. The band was put on the molar, and the coned pin with the tube upon it was forced into the plastic in the cuspid. As soon as this became set, the tube was held permanently, while the bridge itself could be re- moved whenever desired (Fig. 318.) " This method of fixing the tube allows considerable range in its adjustment. In soldering the coned pin to the truss, care should be taken to set it at an angle exactly parallel to the axis of the molar; otherwise there will be difficulty in removing the bridge. " The third style of detachable bridge-work to be described involves the use of cusp crowns (Fig. 319) for supporting posts or piers. Suppose a case similar to that described at page 395, where a bridge is required to extend from the right inferior cuspid to the right inferior second molar, with only the roots of BRIDGE-WORK. 395 the two teeth named as supports. Prepare the roots and pulp- chamber. Set screw-posts into the dentine for anchorage or as retaining-pins, and fit the collars, using sizes wide enough to form the walls of the crowns. Fill the pulp-chamber and about two-thirds of the depth of the collars with a plastic filling material, packing it well around the retaining-posts. Select suitable cusp crowns for the molar and cuspid and place them Fig. 317. Fig. 318. in the ends of the bands to ascertain the occlusion. If too long, shorten the cusps or reduce the bands with engine corundums or rotary files, and Avhen the correct articulation is found form a small square shoulder in the lingual edge of the cuspid and in the posterior grinding surface of the molar. Fill the remain- ing portion of the collars with plastic mixed someAvhat thinner Fig. 319. than the first lot, and set the cusp crowns in position. If there are antagonizing teeth, the mere closing of the patient's jaws will force the crowns to place. If there are no antagonizing teeth the croAvns can be readily tapped to place Avith the mallet, using a piece of wood as a driver. Allow the filling material to set firmly, trimming off any excess which may exude around the collars. Bridge supports or piers constructed on this plan 396 MECHANICAL DENTISTRY. are strong and durable, and likely to withstand any strain. Take an impression, and proceed to fit seamless collars to tele- scope over those already set upon the cuspid and second molar roots. It will be remembered that these collars are so made that each size telescopes into the next higher series. If the proper sizes are selected for the outside or female bands, the work of fitting is readily and quickly accomplished, forming tubes AAmich slide easily over the supporting piers, and at the same time fit closely. It is only necessary to take care in shap- ing the tubes not to drive them too far up on the mandrels and thus stretch them so as to destroy the fit. To the outer end of each of the tubes solder a small piece of gold plate, forming Fig. 320. Fig. 321. partial caps so placed as to rest when in position upon the shoulders previously cut in the cusp crowns. Adjust a truss bar of half-round gold wire, to the ends of Avhich solder the tubes (Fig. 320). The truss is now ready for the teeth, which may be of any of the forms used for this purpose, and they may be attached to the bar in any way desired. One of the strongest attachments is vulcanite. "An easy modification of the plan just described is readily adapted to cases where only a small space is to be filled and one end of the bridge is to be supported by a sound tooth. Thus, suppose it is desired to bridge a space formerly occupied BRIDGE-WORK. 397 by the two inferior left bicuspids, the crown of the first molar being a mere shell. The operation would be essentially the same as in the previous case, except that the sound cuspid would be utilized for one of the piers, as follows: Fit a seamless collar, cut out a portion of it so that it will embrace only about two-thirds of the cuspid crown, and solder a partial cap or cover to it (Fig. 321). Or, the cuspid may be separated from the lateral incisor with the corundum disk and the collar allowed to em- brace the whole crown. " The great desideratum in constructing a piece of bridge- work is, of course the securing of perfect usefulness in mastica- tion and speech, combined with absolute comfort and cleanli- ness. The closer a bridge approaches that condition where its wearer loses consciousness of its presence in his mouth, the nearer perfection it is. Scarcely less important, however, is the necessity of providing for repair. Accidents will occur, and the system which superadds to usefulness, comfort, and beauty, ready facility for repairing breakages is by so much superior to those which make no such provision. The place of a crown broken from a bridge constructed by any of the methods above described can be easily supplied, and the piece when repaired will be as strong and serviceable as it Avas originally." CHAPTER VII. PARTIAL DENTURES RETAINED IN THE MOUTH BY MEANS OF CLASPS ATTACHED TO THE NATURAL TEETH. Remarks on the Use of Clasps.—Clasps, or metallic bands, have been long and very generally employed as a means of retaining parts of sets of teeth in the mouth, and are still used, to a lim- ited extent, for that purpose by many practitioners. When these appliances are skillfully adjusted, and all the conditions pertaining to the mouth and remaining natural teeth are favor- able to their application, they afford a certain, permanent, and satisfactory means of supporting, partial dentures, and may be employed, under such circumstances, with comparative safety to the natural organs. When it is remembered, howTever, that in a lamentably large proportion of cases, clasps are carelessly or unskillfully formed and fitted to the teeth; that the organs of support are often indiscriminately selected, and are neither adapted in form, situation, or structure for such uses; and that they are frequently diseased and insecurely attached to the jaw, or are mutilated for the reception of clasps, we can readily un- derstand to what unlimited extent this method is subject to abuses. In fact, few other special processes in mechanical prac- tice have been so fruitful of evil as that under consideration, and the opprobrium which but too justly attaches to it in pro- fessional as well as popular estimation is chargeable more prop- erly to bad faith and unskillfulness on the part of the operator, and to want of necessary attention to the cleanliness of the substitute and the organs of the mouth on the part of the patient, than to any inherent unsuitableness of the method itself. Nevertheless, it must be admitted that, under the most favor- able circumstances, the teeth clasped are not wholly exempt from liability to injury, and this circumstance in itself renders it the more imperative that the process should be surrounded by all the safeguards that skill and ingenuity can devise. The opinion, at one time current, that the injury inflicted 398 PARTIAL DENTURES RETAINED BY CLASPS. 399 upon the teeth by clasps Avas mainly the result of mechanical action, has given place to the more defensible vieAV that the causes concerned in its production are chiefly of chemical origin. Thus, the secretions of the mouth, with particles of alimentary and other substances, being retained between the clasp and tooth for a sufficient period of time, and exposed to the favoring conditions of warmth and immobility, suffer a process of putrefactive decomposition by which acids are elimi- nated, and which, in their nascent state, act with perceptible energy upon the bone constituents of the tooth, producing disintegration and ultimate decay. The rapidity and extent of this action will depend much upon the nature and quantity of the acids liberated; the structural characteristics and vital resist- ance of the teeth; the mechanical execution, adaptation, and composition of the plate; and the personal habits of the patient with respect to cleanliness. The most usual seat of structural disorganization in these cases is at the neck of the tooth where the enamel is thinnest, and is sometimes limited to a circumscribed spot, but oftener extends on a line Avith the gum involving nearly or quite all of that part of the neck of the tooth embraced by the clasp. At first the enamel becomes bleached and softened as though macerated, and is ordinarily Arery sensitive to both chemical and mechanical irritants. Yrith a continuance of the cause, the superficial portions of the affected parts become more and more thoroughly disintegrated, and sooner or later assume the open form and characteristics of ordinary decay. If, as was formerly supposed, decay or solution of tooth-bone in these cases resulted from mechanical attrition, or wearing away of the enamel, the injury would be inflicted at points distant from the neck of the tooth Avhere the clasp lies in more direct and immediate con- tact with the protuberant portions of the crown; but we find that decay, from this cause, is not only of infrequent occur- rence at such points, but, on the contrary, the enamel here is frequently found condensed and polished by the mechanical action of the clasp. Certain conditions of the plate and clasp undoubtedly favor mechanical action and accelerate the destruc- tion of the tooth; as where the clasp bears unequally with sharp 400 MECHANICAL DENTISTRY. and unfinished edges upon the tooth, or where the base is faulty in its adaptation to the mouth, admitting, by its mobility, of irregular traction or pressure upon the organs of support. Whenever the artificial appliance is thus unskillfully constructed and applied, and free interspaces are furnished for the lodg- ment and retention of particles of food, and the teeth clasped are defective in structure, and we have conjoined with these an utter disregard of cleanliness in regard to the substitute and remaining natural teeth, the destruction of the latter is certain, rapid, and generally irretrievable. The Teeth to which it is most proper to attach Clasps.—The utility, comfort, and appearance of a partial set of artificial teeth in the mouth will depend much upon the fitness of the natural organs selected for the purpose of support. "A clasp," says Professor Harris, "should never be applied to a loose tooth, or to one situated in a diseased socket, or which is so much affected by caries as to render its perfect restoration and per- manent preservation impracticable, and when none but such can be had, the proper course to pursue is to extract every tooth in the jaw, and replace the loss of the whole with an entire upper set. The application of clasps to diseased or loose teeth, always aggravates the morbid condition of the parts, and causes the substitute which they sustain, to become a source of annoyance to the patient. Besides, such teeth can be retained in the mouth only for a short time, and when they give way, the artificial appliance becomes useless, and even while it is worn, it is not held firmly in place, but is moved up and down by the action of the lips and tongue, so that its pres- ence can hardly escape observation from the most careless observer."* Teeth, also, that are too short to admit of sufficient breadth to the clasp to impart stability to the substitute, and those that stand very irregularly in the arch, rendering it difficult for the patient to apply and remove the appliance, are unsuitable as organs of support. In reference to the individual classes of teeth, it may be observed that the incisors, both as regards form and situation, * Principles and Practice of Dental Surgery, page 717. PARTIAL DENTURES RETAINED BY CLASPS. 401 are inadmissible for clasping, and are, therefore, never used for this purpose. The cuspidati, likewise, being placed conspicu- ously in the front part of the mouth, cannot be securely embraced without manifest exposure of the clasp; besides, the conical form of these teeth makes the use of a very slender clasp indispen- sable ; hence, these teeth are rarely employed, and may only be used when, in the judgment of the operator, the necessities of the patient for the time being seem to require it. Either the anterior or the posterior molars, wdien sound and firm, offer, in respect of their general conformation and position in the arch, the most desirable and efficient support for parts of sets of teeth. The crowns of these teeth generally afford ample breadth to the clasp; have nearly parallel walls; and furnish, by the strength and immobility of their attachments to the jaAV, the greatest security to the artificial appliance. The anterior molars are preferable where these are remaining in good condi- tioner are susceptible of being properly restored and preserved if diseased or carious. Of the bicuspids, the posterior are to be selected, if practicable, as these better favor the concealment of the clasps; to effect which more perfectly, in the use of either the first or second bicuspids, it will be sufficient in many cases to embrace only the posterior half of the crown. The dentes sapientise, or wisdom teeth, will seldom admit of the application of clasps, as the crowns of these teeth are usually very short and cone-shaped, the walls converging abruptly from the gum; besides, the retractive forces applied to the anterior teeth of the substitute would, on account of the increased leverage consequent upon the extension of the plate back to these teeth, tend either to disengage the clasps or produce dis- placement of the teeth to which they are applied. In supplying the loss of one or more of the inferior incisors, the appliance should, as a general thing, be attached either to the anterior or posterior bicuspids, as these teeth stand more nearly vertical in the arch. In fixing partial lower dentures, it will be sufficient to simply provide against mobility of the base, as they are favored rather than opposed, as above, by gravita- tion. The replacement of the inferior teeth posterior to one or 26 402 MECHANICAL DENTISTRY. both bicuspids, however, are more frequently demanded; in which case it is customary to attach the clasps to the teeth immediately in front of and adjoining the vacuities on each side. It will not, however, be necessary to attach clasps in these cases whenever the edentulous portions of the jaw present a distinctly scooped form, or marked concavity of outline, forming a kind of bed for the plate. If, on the other hand, the ridge falls back with a tolerably uniform inclination from the teeth in front, Avith no sufficient elevation at the base of the coronoid process, it may become necessary to provide against backward displace- ment of the substitute by attaching clasps, as before stated, to the teeth immediately in front. In any case, if the dentes sapientiae remain, partial or stay clasps may be attached to each heel of the plate, and so adjusted as to rest against the anterior face of these teeth, obviating entirely the necessity of clasps in front. Separation of the Teeth, by Filing, for the Reception of Clasps.— The practice of separating the teeth with the file to pro\dde for the application of clasps should always be avoided if practicable, since the liability of the teeth thus denuded of enamel to decay is greatly increased under circumstances so favorable to their disintegration. In the case of young subjects, especially, where the teeth are but imperfectly consolidated, and in adults whose teeth are defectively organized, presenting but a feeble resist- ance to the disintegrating agents usually present in the mouth, the use of the file, for the purpose indicated, is eminently per- nicious, and should never be resorted to until every other means of supporting the artificial appliance have been fairly and pa- tiently tried. Whenever a plain necessity for this operation exists, a careful examination of all the teeth to which it is proper to apply clasps should be made, and if decay is found upon their proximate surfaces, the separation should be made between the teeth so affected; and this circumstance should, in most cases, deter- mine the selection, though the affected tooth or the one adjoin- ing may not be esteemed, in other respects, the best for the purposes of support. If decay exists on the proximate surface of only one of the teeth to be separated, a safe-sided file should PARTIAL DENTURES RETAINED BY CLASPS. 403 be employed, and the filing confined entirely to the carious tooth, leaving the enamel of the one adjoining unbroken. The cavity of decay should be Avell filled, and the filed surface thoroughly condensed and polished with a burnisher. Modifications in the Form of Clasps.—1. Plain Band. The most usual form of clasp is that shown in Fig. 322. It consists of a plain metallic band of greater Ftp 322 or less AAridth and thickness, and is made to embrace the larger portion of the circumference of the tooth. In regard to the general properties of metallic clasps, it may be said that they should be, as nearly as practicable, of the same quality or fineness as the plate or base to which they are united; they should be heavy enough to impart adequate security to the attachment, say twice the Fig. 323. thickness of the base, and exceeding this in some cases; and sufficiently elastic to embrace accurately the more contracted parts of the teeth after having been temporarily forced apart in passing over the enlarged portions of the crowns. In construct- ing a plain band or clasp, a strip of sheet lead or other pliable substance may first be fitted accurately to the plaster tooth, making it of the required width, and shaping the edge next the gum in conformity with the irregularities in the latter around the neck of the tooth; the exact counterpart of the pat- tern thus obtained is then cut from the plate to be used in the 404 MECHANICAL DENTISTRV. formation of the clasp. The strip thus obtained is then bent with round-nosed or grooved pliers (Fig. 323), until conformed as perfectly as possible to every portion of the surface of the tooth embraced by it. This coaptation should be sufficiently accurate to exclude perfectly all solid substances from between the clasp and the tooth. A more accurate adaptation of the clasp may be secured in the following manner: First secure a pattern, as before described, and by this cut from a thin strip of platinum, say No. 30 or 32 of the gauge-plate, a band of the required size and form, and press or burnish it accurately to the form of the plaster tooth. The soft and pliant condition of this metal v\rill admit of its being easily adapted to any irregu- larities upon the lateral walls of the tooth. The band thus molded to the tooth is then carefully removed from the model, or the mouth, if fitted to the tooth in the latter, and its central portion filled with a mixture of plaster and sand with a small metallic wire or bar passing through the centre to support it while soldering. The outer or exposed surface is then smeared with a mixture of borax, and small scraps or fragments of gold plate of equal fineness with the main plate, are placed at inter- vals and fused with the blowpipe until diffused uniformly over the surface. Small pieces may be added from time to time, until the required thickness of the clasp is obtained. The piece should be heated uniformly throughout to induce an even Aoav of the gold over the exterior surface of the platinum ring. By this method a faultless adaptation of the clasp to the tooth may be secured, provided the form of the latter is correctly repre- sented on the model. In all cases where the plain band is used, it should be made as broad as the tooth will admit of, as a clasp so formed gives greater stability to the plate, and does not endanger the tooth clasped in any greater degree than a narrow one. 2. Standard Clasp.—To guard more perfectly against the retention of vitiated secretions and particles of food around the neck of the tooth, a method of constructing clasps has been devised and introduced to the notice of the profession by Dr. C. W. Spalding, which, by leaving the cervical portion of the tooth in a great degree uncovered, permits the action of the PARTIAL DENTURES RETAINED BY CLASPS. 405 tongue and the natural circulation of the fluids of the mouth to Avash or cleanse that portion of the tooth most liable to be injuriously affected. In commenting on this method, Dr. S. remarks: " The writer has for many years been in the habit of employing narrow clasps for the purposes of support, making them of sufficient thickness to give the required strength, and attaching them to the plate by means of standards, so arranged as to induce the removal of accumulations between the clasp and tooth, by the circulation of the saliva (Fig. 324). The use of one or more standards as a means of attachment, also pro- vides, by a variation of their length, for the grasping of the tooth at any desired point. If the tooth is long, and particu- larly if it is at the same time bell-crowned, the point selected should be toward the grinding surface, as far from the gum as is found practicable. If the tooth is short and of such form that it can be successfully clasped at no other point than that near the gum, the plate should be cut away at least one or one and a half lines from the tooth, and standards introduced for the purpose of promoting circulation, by affording a free pas- sage for the ingress and egress of fluids. These standards should also be narrow, no wider than the clasp itself, and should con- stitute the only point of union between the clasp and plate. Half-round wire Avill be found to be a very convenient article for making clasps. The particular form of the clasp is, howrever, immaterial, if it is both narrow and strong."* 3. Scalloped Clasp.—SomeAvhat analogous in form to the clasp just described, and constructed Avith a similar design, is the one recommended by Dr. B. T. Y7hitney. A plain band of gold is fitted to the tooth in the manner first described, when that por- tion of it next the gum on the lingual side of the tooth is scalloped or cut aAvay in the form of a semicircle or arch, the ends of the clasp being in like manner narroAved sufficiently to relieve them from contact wdth the neck of the tooth. The intermediate points of the clasp which serve to unite the latter to the base may be two or more in number, and should be wide enough to impart adequate strength to the attachment. A clasp so formed and applied to the base Avill present very nearly the ap- * American Dental Review, vol. i, p. 12. 406 MECHANICAL DENTISTRY. pearance of the standard clasp as represented in Fig. 324. Dr. W. recommends soldering but a single point at first, and then hav- ing tried the plate in the mouth and adjusted the clasp properly to the tooth, remove and solder the remaining point or points. 4. Partial or Stay Clasp.—This form of clasp, instead of em- bracing the tooth, is designed to steady or fix the substitute in place by simply resting against one side of the tooth to Avhich it is applied. (Fig. 325.) They should be so connected to the plate that, when pressed over the enlarged portions of the crowns of the teeth, they will spring readily into place and adapt them- selves closely to the more contracted parts near the gum. In cases where there is no adequate opposing force to that exerted by the clasp, care should be taken that no more pressure is pro- duced than is necessary to keep the substitute in place, as, without this precaution, outward displacement of the teeth is Fig. 324. Fig. 325. liable to occur, and the appliance, losing its bearing upon the teeth, soon becomes loosened and insecure in the mouth. The result alluded to should be particularly guarded against in the case of young subjects, whose teeth are easily moved by the application of very slight forces. Modifications in the Form of Plates for Partial Dentures Supported in the Mouth by Clasps.—-The particular form and dimensions of a plate, when clasps are used, will be mainly determined by the number and position of the teeth to be replaced, and by the location of the natural organs to which the clasps are attached. It will be sufficient in this place to indicate the leading forms as they relate to the substitution of the several classes of teeth. In supplying the loss of a superior central or lateral incisor, it will be sufficient in many cases to attach the plate to either a PARTIAL DENTURES RETAINED BY CLASPS. 407 bicuspid or molar on the same side, as in Fig. 326. If two or more of the front teeth, however, are to be replaced, it is better to extend the plate on each side of the palatal arch, and attach to a bicuspid or molar (Fig. 328); or to a bicuspid on one side, and a molar on the other; unless two firm and well-formed Fig. 326. teeth on the same or the opposite side can be commanded (Fig. 327), while those upon the other could not be employed without a separation. In all cases where it is necessary to extend a narrow plate from the extreme front part of the mouth to a single tooth situated posteriorly in the arch, the former should Fig. 327. Fig. 328. be strengthened by soldering a narrow rim of plate or half- round Avire along the border next the teeth, and the clasp should, whenever practicable, pass in front of and embrace the anterior face of the tooth to which it is applied. If an anterior bicuspid is to be replaced, the plate may be 408 MECHANICAL DENTISTRY. attached to the adjoining bicuspid (Fig. 329, right side), or if both are absent, then to the first molar (Fig. 329, left side), or the clasp may embrace both of the latter if remaining and no separation between them exists. Fig. 330 represents the form of a plate supplying the loss of teeth at intervals, the clasp on one side embracing the posterior bicuspid in front and extend- ing round the back part of the adjoining molar. Fig. 331 represents the form of plate supplying the loss of the two bicuspids on one side, and the anterior bicuspid and molar on the opposite, the plate being attached to an anterior molar and second bicuspid. The antero-posterior extension of the plate, as exhibited in connection with the bicuspid tooth, greatly favors the stability of the substitute, and, provided the plate and clasp are accurately fitted to the parts, the support afforded Fig. 329. Fig. 330. by a bicuspid tooth under such circumstances is equivalent to that furnished by a firm and well-formed molar clasped as shown on the opposite side. A base so supported may be made to sustain any number of teeth with the greatest se- curity. Either the anterior or posterior molars, if firm and securely attached to the jaw, will afford adequate support to a plate replacing all of the teeth anterior to them. (Fig. 332.) Even a single molar situated on either side of the arch, if similarly circumstanced, may be made to sustain, with tolerable firmness, a base supplying the loss of all the remaining teeth—though, ordinarily, it is better to extract such a tooth and substitute an entire upper denture. In all cases, where any considerable PARTIAL DENTURES RETAINED BY CLASPS. 409 number of teeth anterior to those clasped are to be replaced, and a vacuity on the ridge exists posterior to the latter, the plate should be extended back and overlap the ridge (Fig. 333), the latter affording a counter-point of resistance when traction is made upon the anterior teeth, thus directing the forces applied Fig. 331. Fig. 332. more on a line Avith the long axes of the teeth that sustain the appliance. In supplying the loss of the inferior molars and bicuspids, or any number of these teeth> the form of plate represented in Fig. 334 is generally employed. The parts of the plate over- Fig. 333. Fig. 334. lapping and resting upon the ridge behind, are connected with each other by a narrow strip of plate extending round the ridge in front on the lingual side of the anterior teeth. This latter portion of the plate should be accurately swaged to the form of the gum on which it rests, and should be made narrowT 410 MECHANICAL DENTISTRY. enough to avoid encroaching upon the reflected portion of mucous membrane, the glands beneath the tongue, or the frse- num linguse. To avoid wounding these parts, and to allow them unobstructed play, it will be necessary to make this por- tion of the plate quite narrow; and as a single thickness of plate would not impart adequate strength, it is customary to double this connecting band—the duplicate band extending back to the lateral wings of the plate, and crossing them ob- liquely, as indicated by the dotted lines in Fig. 334. Additional strength will be given by doubling the entire plate, but this is not generally required. The outer border of those portions of the plate overlapping the ridge may be turned up to the depth of from half a line to a line to form a groove or socket for the reception of the ends of gum teeth, or blocks, if such are used; while the inner margins should terminate in a rounded edge, extending from heel to heel of the plate, this form' being given to it either by turning the edge over and filling in the groove with solder, or by soldering a narrow strip of plate or half-round Avire along the border. The circum- stances or conditions which make the use of clasps necessary in these cases, as well as those, also, which contraindicate their employment, have already been noticed. The practice of ex- tending a narrow band or wure from the sides of the plate round he outer border of the ridge in front of the anterior teeth, to prevent a backward displacement of the base, is liable to produce irritation and tenderness of the mucous membrane immediately over the roots of the anterior teeth, and should, therefore, never be resorted to, unless there are no teeth remain- ing to which clasps may be applied. If the appliance is designed to restore the loss of teeth recently extracted, and where but little or no change has oc- curred from absorption of the parts, the portions of the plate which pass in between the adjoining teeth should terminate a line or more within the outer circle of the remaining teeth; and where the space, if it happens in the front part of the mouth, admits of tAvo or more teeth, the edges of the extended portion of plate should be scalloped in correspondence with the festoons of the gum, as seen in Fig. 335. In such cases, plain or plate PARTIAL DENTURES RETAINED BY CLASPS. 411 teeth, by Avhich is meant those which represent only the crowms of the natural organs, should be employed; these, resting on the edge of the plate, will overlap somewhat, with their anterior edges resting directly upon the gum in front, taking the place occupied by the croAvns of the extracted teeth. On the other hand, if sufficient time has elapsed after the extraction of the teeth to permit the changes in the form of the ridge to occur incident to partial or complete absorption of the parts, and a greater or less concavity exists betAveen and above the teeth on the outside of the jaAv, the plate, Avhere it passes into the interspace, should extend some distance over the border of the ridge. Swaging or Stamping the Plate.—Having determined upon the proper form and dimensions of the plate for any given case, its outlines may first be traced upon the model; from this an exact pattern in lead may be obtained, or the pattern may be suffi- ciently ample to partially overlap the cut extremities of the teeth wdien the latter are not represented upon the die, having been previously cut from the model, as shown in Fig. 73. The outlines of the pattern are then traced upon the plate of gold or other metal to be used for the base. The redundant portions of plate are then cut away Avith plate shears and for- ceps, and the edges trimmed smooth with a file. A very con- venient and almost indispensable instrument for cutting away the plate in conformity with the palatal curvatures of the teeth, is a plate forceps as exhibited in Fig. 336. The plate cut to the proper form is now placed upon the die and brought as nearly as possible into adaptation with a wooden or horn mallet; it is then placed between the die and counter, the latter resting on an anvil or other equally resisting surface, when the two metallic pieces are brought forcibly together Avith a few steady and wrell-directed blows of a heavy hammer. Tilting of the die, resulting sometimes unavoidably from a one-sided bloAV, may be obviated by placing a cone-shaped piece of cast iron, brass, or zinc over the die, the base of the 412 MECHANICAL DENTISTRY. cone resting on the back of the die; by this expedient the force of the blow is equalized and concentrated more directly over the die. The metallic swages should at first be brought cau- tiously together, and should be separated after the first blow or two to enable the manipulator to detect and remedy any mal- position of the plate before it becomes intractable from con- tinued swaging. If, in the process of stamping, any portion of the plate is found cracking or parting, its further extension at that point may be prevented by flowing a little solder at the termination of the fissure. During the progress of SAvaging, the plate should be frequently annealed, which is done by bringing it to a full red heat under the blowpipe, or by placing it in the furnace; the plate is thus rendered more pliant and can be more readily and perfectly forced into adaptation to the irregularities on the face of the die. Fig. 336. If, after somewhat protracted swaging, the plate is not con- formed perfectly to the face of the die, another and unused counter should be substituted for that in use; and, indeed, it is better in all cases to have duplicate copies both of the die and counter in reserve with which to complete the swaging, inasmuch as more or less deformity of both swages unavoid- ably occurs before the plate is brought into very accurate coaptation with the die. The stamping conducted thus far, the plate may be applied to the plaster model, and if found too full at any points, it should be trimmed with a file to the exact dimensions required. The margins of the plate adjoining the necks of the teeth should be permitted either to lie closely to them, or should be cut away, leaving a space equal to a line or PARTIAL DENTURES RETAINED BY CLASPS. 413 more between the plate and the teeth; for if but a A'ery narroAV line of uncovered gum remains at these points, injury to the parts immediately surrounding the necks of the teeth is more liable to occur from strangulation of the interposed gum than if the plate were further removed from the teeth or rested directly against them. If the portion of the plate which passes in between the remaining teeth is quite narrow, as where but a single tooth is to be supplied, it should be strengthened by wiring the edges or doubling the plate at such point. It is also advisable in many cases, in order to provide more perfectly against fracture or distortion of the base in mastication, to wire or double the entire border of the plate adjoining the necks of the teeth. Narrow bands of gold resting against the necks of the teeth, constructed and adjusted after the manner of stay clasps, are sometimes soldered to the edge of the plate next the teeth ; but unless the substitute is frequently removed from the mouth and cleansed, as well, also, as the teeth to Avhich they are applied, serious injury is likely to be inflicted upon the teeth implicated. The edges of those parts of the plate occupying the vacuities on the ridge should be filed thin to admit of a more accurate adaptation of the artificial with the natural gum, and should not, as before observed, ordinarily extend beyond the outer circle of the contiguous teeth, allowing the gum extremity of the artificial tooth to overlap and rest directly on the natural gum above. If, however, the concavity between and above the teeth on the external border of the ridge is considerable, the interdentinal portions of plate should overlap the border com- pletely and underlie the porcelain gum. Uniting the Plate and Clasps.—Having proceeded thus far in the operation, the plate and clasps should next be united to each other, and the utility and comfort of the appliance in the mouth, as Avell as the safety of the natural organs used for the purpose of support, will depend, in a great measure, upon the accurateness of the relation of the several parts of the appli- ance to the organs of the mouth; it being a matter of primary importance that the various parts of the substitute should be so adjusted to the remaining teeth—especially those to which the 414 MECHANICAL DENTISTRY. clasps are applied—and the ridge and palate, that it shall not, in any material degree, act as a retractor upon the organs of support, or furnish interspaces for the lodgment of food, while at the same time it should be so fitted as to be easily removed and applied by the patient. The clasps having been fitted to the plaster teeth and the base swaged to the form of the palatal arch and ridge, the plate is placed in its proper position in the mouth and an impression in wax taken of the latter with the plate in place. The impres- sion, with the plate adhering, is then removed from the mouth, its surface oiled and a model obtained in the manner heretofore described. If, in separating the model and impression, the plate adheres to the latter, it should be detached and adjusted to the model and the clasps arranged upon the plaster teeth. The plate and clasps may now be bound to the model with an- nealed wire, and united to each other with solder; but the better way is to attach them to each other temporarily, with adhesive wax, in the relation they occupy on the model, and then remove them carefully and imbed the clasps and palatal face of the plate in a mixture of nearly equal parts of plaster, sand, and asbestos. Before uniting the two pieces on the model with wax, however, the ends of the clasps should be straight- ened out or spread apart, in order that they may part readily from the plaster teeth, without, in any degree, changing their exact relation to the plate; in doing which, it should be ob- served that all parts of the clasps which are to be united to the plate should remain in close contact with the plaster teeth. After the plaster mixture, in which the plate and clasps are imbedded, has become sufficiently hard, the portions of wax which temporarily united the latter should be removed, and the surfaces of the clasps and plate, where they unite with each other, smeared with borax ground in water to the con- sistence of cream; small pieces of solder are then placed along the lines of contact, the investient heated in the furnace until the plate acquires a full red heat, Avhen it is removed, placed upon a suitable holder, and the solder fused with the blowpipe. YThenever the form and inclination of the teeth to be clasped PARTIAL DENTURES RETAINED BY CLASPS. 415 are not fairly represented on the model, owing to dragging or displacement of the wax in withdraAving the impression, the difficulties of securing a proper relative adjustment of the sev- eral parts of the appliance will be increased; but either of the following methods, if carefully and accurately manipulated, will secure accurate results:— 1. Plaster-of-Paris, gutta-percha, or modeling compound, may be substituted for wax when taking an impression with the plate in the mouth. YTith the proper use of these materials, the exact form and inclination of the teeth will be better preserved; and when employed they should be filled in with plaster for the model immediately after removing them from the mouth. The subsequent steps in the operation are precisely similar to those described wThen wax is used. 2. Another method is to adjust the clasps and plate to the parts in the mouth, attach them temporarily in their proper relation, and remove, invest, and solder in the usual way. This may be accomplished in the following manner: First, spread apart the ends of the clasp somewhat to permit it to be easily removed from the tooth; place this upon the tooth in the mouth to be clasped; then adjust the plate in the mouth, and attach the two to each other by pressing a piece of stiff, adhe- sive Avax in against the clasp and plate where they unite; harden the wax by placing against it, for a few minutes, the end of a napkin moist with cold water; then remove the plate and clasp carefully from the mouth, and invest and solder as before. The plate, with one clasp permanently attached, is now placed back in the mouth, and the second clasp adjusted to the tooth on the opposite side in the manner before alluded to; this is then temporarily fastened to the plate and otherwise treated in like manner as the one first described. If the teeth to be clasped are favorably formed and regularly arranged in the arch, both clasps may, at the same time, be temporarily attached to the plate in the first instance; if not, it will be impracticable to remove them from the teeth without disturbing the wax and changing their relation to the base and the teeth clasped. The additional labor and consumption of time incident to a sepa- rate attachment of the clasps, will, in proportion as they 416 MECHANICAL DENTISTRY. secure better results, amply reward the operator for his pains- taking. Plaster is sometimes substituted for wax in this process; in which case it is introduced into the mouth on a small piece of wax or sheet lead and pressed gently against the uniting por- tions of the plate and clasp, and allowed to remain until suffi- ciently hard. Any superfluous portions around the tooth that may hinder the easy removal of the clasp should now be cut away, Avhen the pieces so attached to each other are removed from the mouth. A separation of the plaster from the clasp or plate, or both, may occur when removing the latter; in this case the several parts may be readily and accurately adjusted to each other again in their exact relation when out of the mouth, as the. latter will be plainly indicated by the impression made by the plate and clasp in the plaster. Being readjusted, they may be further secured by sticking them together with a little soft- ened Avax, when they are invested, the temporary fastenings of plaster removed, and the pieces united by soldering. The use of plaster in these cases is due to Dr. Lester Noble, and unques- tionably possesses many advantages over wax for the purpose, as the latter is liable, even with the most skillful manipulation, to become displaced in removing it from the mouth; and this change, when it occurs, not being indicated by inspection of the wax, is incapable of timely correction. 3. Still another method is that contrived by Dr. Fogle and described by Dr. Cushman in the tenth volume of the American Journal of Dental Science. It consists in securing the proper relation of the clasps to the teeth in the mouth by the use, in the first instance, of what are termed " temporary fastenings." The plate and clasps are first applied to the model, and are then connected by a narrow strip of plate or piece of wire bent in the form of a bow, the concavity facing the model, one end of which is soldered to the palatal side of the clasp, and the other to a contiguous point upon the plate, as exhibited in Figs. 337, 338, and the pieces thus temporarily united are removed from the model and adjusted to the parts in the mouth. If the position of the clasps is found in any respect faulty, they can be easily and accurately adapted to the walls of the teeth by bending or PARTIAL DENTURES RETAINED BY CLASPS. 417 twisting the connecting strip in any desired direction with pliers or other instruments suitable for the purpose. This accom- Fig. 337. plished, the plate and clasps are removed, and the operation of permanently uniting the clasps to the plate performed in the usual manner. CHAPTER VIII. PARTIAL DENTURES SUPPORTED IN THE MOUTH BY MEANS OF CYLINDERS OF WOOD ATTACHED TO TUBED PLATES. The following description of a method of supporting partial sets of teeth in the mouth by means of wood cylinders attached to the plate is copied from an article contributed by Dr. W. M. Hunter to the fourth volume of the American Journal of Dental Science. The same principle had long been made available in Europe in attaching artificial substitutes constructed of the hippopotamus ivory, but the credit of its application to metallic plates is alike due to Drs. Hunter and Charles Stokes of London. " After swaging, the plate, as usual, is tried in the mouth, and an accurate impression of the teeth to be used is taken over the plate, as recommended by Dr. Arthur, in the American Journal, Avhich will show the exact position of the tooth in its relation to the plate; after which the edge of the plate sur- rounding the teeth to be made use of, should be doubled or wired, when the tubes may be soldered at their proper points, taking care never to apply pressure to one side of a tooth with- out some means of counteracting the effect; the means being either a sufficient number of natural teeth contiguous to the tooth to be used, a counter-tube, an arm of metal, or an arti- ficial tooth, depending entirely upon the nature of the case. " At times, it is well to tube but one side of the plate and clasp the other; in cases where the crown of the tooth is much larger than the neck, a beautiful application may be thus made. " The tubes should be from one-eighth of an inch to one line in diameter, and should be filled Avith whiting before applying heat, to prevent them from filling with solder at the time of soldering to the plate. They should be placed upon the plate so carefully, that the mouth of the tube will come in contact Avith the natural tooth, as it is desirable to have the wood protrude but very slightly beyond the orifice. 418 PARTIAL DENTURES RETAINED BY WOOD CYLINDERS. 419 " When it can be properly done, the tubes are soldered at the same time the teeth are, as it saves much trouble in fitting; it cannot, however, be very well done where it is designed to fit a tooth over a tube, but can A^ery readily be done where the tooth is designed to fill the angle caused by the meeting of the stay and plate, in the incisors and canine teeth, and where a canine is used for a bicuspid, building over the tube with metal to form the inner cusp." The accompanying cuts show clearly the form and applica- tion of the tubes referred to. In Fig. 338, showing on one side but a single tube, the counter-force is obtained by the artificial tooth which rests against the anterior face of the one to which the wood cylinder is applied. Fig. 339 exhibits tubes arranged on one side, and a clasp on the other; and shows the substitu- Fig. 338. Fig. 339. tion of a canine for a bicuspid, with an inner cusp built up over the tube, practically converting a cuspid into a bicuspid tooth. In commenting on the application of this principle to partial sets of teeth, Dr. H. remarks: " The advantages in many cases must be apparent to the thinking dentist, but, perhaps, it might not be amiss to enumerate a few. " The fixture is held in place with greater firmness than by means of clasps. " In some instances where I have used clasps, I have also used the tube in combination, to give stability for masticating purposes. " The injury to the natural teeth must be much less, owing to the smaller amount of surface in contact. 420 MECHANICAL DENTISTRY. " If decay should take place, it would require but an ordinary filling to restore the tooth. " It prevents that peculiarly disagreeable sensation experi- enced, particularly in fruit season, upon removing and replacing artificial teeth. "After having tested it for more than a year, I am satisfied that it greatly lessens the chances of decay in those cases where it can be applied, and I have removed the clasps in some old cases with great satisfaction to my patients." CHAPTER IX. REMOVABLE PARTIAL DENTURES SUPPORTED IN THE MOUTH BY ATTACHING THE PLATE TO THE ROOTS OF THE NATURAL TEETH. A limited number of teeth may be mounted on a plate attached to the roots of two or more of the front teeth; and pro- vided the latter are firm, well formed, and in a healthy condi- tion at the time of the operation, an appliance so adjusted may be worn by the patient witli comparative comfort and efficiency for a considerable period of time. Ordinarily, the roots of the cuspidati afford the most secure means of attachment, and will furnish adequate support to a Fig. 340. Fig. 341. substitute supplying the loss of a part or all of the teeth anterior to the bicuspids (Fig. 341), and, in some cases, one or two of the latter on each side. The roots of the incisors, also, may be used, or one of the latter and a cuspid. In some cases the plate may be secured in the mouth by attaching to a root on one side, or in front, and clasping to a tooth on the opposite side (Fig. 340), provided the crown of the latter and the supporting root stand nearly or quite parallel with each other, as any considerable deviation from this relation will render it difficult or impossible to apply and remove the substitute. The roots of the teeth to be used as a means of support should be prepared in the manner described under the head of " Root Crowning." In all cases, the enlarged canal of the root should be provided with a gold tube, as this method is the 421 422 MECHANICAL DENTISTRY. only one which will protect the root from the mechanical action of the dowel-pin, or permit a ready and frequent removal of the appliance for the purpose of cleansing it and the parts asso- ciated with it in the mouth. The roots being prepared in the manner indicated, an impres- sion of the mouth is taken, and with a die and counter obtained from a plaster model of the parts, a plate of the required form is swaged covering the filed extremities of the prepared roots, and extending anteriorly very nearly or quite to the free margins of the gum in front. The plate, at those points cor- responding with the openings into the roots, is then perforated and enlarged sufficiently to admit of the passage of the metal- lic pins; the form and position of the orifices in the roots being transferred to the metallic die, the corresponding depres- sions in the plate at these points, when the latter is swaged, will serve as a sufficient guide in perforating the plate for the pins. The plate is now applied to the mouth, and the metallic pin, one-half longer than that ultimately required, and formed to fit the tube accurately but not tightly, is passed through the open- ing in the plate and pressed to the bottom of the tube, leaving the surplus portion of the pin projecting on the lingual side of the plate. The plate and pin are now secured in this pre- cise relation by imbedding the projecting portion of the latter and the parts of the plate immediately surrounding it, in a batter of plaster. When the plaster has hardened, the plate and pin, with the plaster attached, are removed in their un- disturbed relation from the mouth. To preserve the several pieces in situ more perfectly, the projecting end of the pin may be flexed, or roughened with the file before applying the plaster; the pin thus secured will bring all parts together if traction is made on the plate in the act of withdrawing it. The plate being removed from the mouth, its palatal portion is imbedded in the plaster mixture, and when the latter is hard, the plaster is removed from around the pin on the opposite side of the plate, and the pin permanently united by flowing solder at its point of contact with the plate. The redundant portion of the pin on the lingual side of the base is then cut and filed away even with the surface of the latter. If the man- ATTACHING REMOVABLE PLATES TO ROOTS. 423 ipulations have been accurately conducted, the plate and pin, on being reapplied to the parts in the mouth, will be found to adapt themselves perfectly to the palatal arch and roots. It is better, unless the supporting roots stand nearly or quite parallel, to adjust and solder but a single pin at a time, as but a very slight variation in the direction of the roots would render the withdrawal of both pins at the same time difficult or impracticable without more or less change of relation. The same may be remarked of those cases where a clasp is used in conjunction with the pin. The most efficient method of rendering the appliance station- ary when applied to the roots, and at the same time of enabling the patient to readily apply and remove it at will, is that recom- mended by Dr. Dwinelle, and which consists in splitting the pin with a fine saw, and spreading the sections apart some- what, thus giving them an increased lateral bearing. Gold used for dowel-pins in these cases should be alloyed with platinum, as that ordinarily employed for plate is too inelastic for the purpose. CHAPTER X. PARTIAL DENTURES SUPPORTED IN THE MOUTH BY ATMOS- PHERIC PRESSURE OR ADHESION. The method of attaching partial sets of teeth to the superior jaw by means of atmospheric pressure, or by adhesion, is much more generally practiced than formerly, and whenever the con- dition of the soft parts of the mouth, the general configuration of the palatal arch, and the antagonism or occlusion of the artificial with the natural teeth favor its adoption, there are good and sufficient reasons why either of these forces should, in all practicable cases, be utilized in preference to the use of clasps for purposes of attachment. Modifications in the Form of the Base.—If vacuities exist at various points on the ridge, the plate on which the teeth of replacement are mounted, should be ample in its dimensions, covering nearly or quite all of Fig. 342. * the hard palate. The general form of the base, where several teeth scattered throughout the arch are required, is shown in Fig. 342. In most cases, whether but one or a greater number of teeth are to be replaced, increased adherence and stability of the substitute will be better secured by permitting the plate to cover the larger portion of the roof of the mouth; though, in cases that present the best form of the vault, a diminished surface may be given to the base with equally satisfactory results. In the substitution of a single incisor, for example, it will fre- quently be sufficient to employ a very small plate covering only a part of the anterior sloping wall of the palate. (Fig. 343.) In the latter case, the plate used may be very thin, say No. 30 standard gauge; it will thus impede the movements of the 424 PARTIAL DENTURES HELD BY ATMOSPHERIC PRESSURE. 425 tongue less, and may be swaged more accurately to the parts. If constructed with an air chamber, the latter should be quite shallow. A somewhat anomalous form of atmospheric-pressure plate employed in the substitution of one or two bicuspid teeth on each side is described by Professor Taft,* the design of which is to secure, in such cases, increased stability of the substitute, while much of the palatal arch is left uncovered. It consists, as will be seen by reference to Fig. 344, of two lateral cavity plates accurately adjusted to the sloping walls of the palate on each side, immediately adjoining and partly occupying the spaces to be supplied. These lateral plates may be made as large as a dime, or somewhat larger, and of an elliptical shape if both bicuspids on the same side are to be replaced, and are Fig. 343. Fig. 344. connected with each other by a narrow band of gold plate, two lines or more in width, having an anterior curvature, and rest- ing on the front wall of the palate, two or three lines behind the anterior teeth. The entire appliance may be constructed from a single piece of gold plate swaged accurately to the parts ; or the lateral plates and connecting band may be sepa- rately swaged and secured in their proper relation to each other in the mouth with wax or plaster, when they are carefully removed, invested, and soldered together; it should then be re-swaged to correct any change of relation that may have happened during the concluding manipulations. The liability of the plate to ride upon the central and raised portion of the * Dental Register of the West, vol. xiii, p. 112. 426 MECHANICAL DENTISTRY. palate, when pressure is made upon one side, throwing the plate off from the ridge on the other, as in the case of a base extending across the arch, is in a great degree obviated by the method just described. Manner of Forming an Air Chamber.—Atmospheric-pressure plates for partial cases are constructed with a central air chamber; in which case, the part of the model representing the chamber may be formed in either of the ways mentioned in the chapter on " Plaster Models." The model prepared, the form of the plate to be used is first indicated thereon, and from this a pattern in sheet lead is obtained, which is placed on the plate of gold or other metal, and its outlines traced with a pointed instrument; the redundant portions are then cut away with plate shears and forceps. The plate is now placed on the die, and brought as nearly as possible into adaptation to the latter with the mallet and pliers; it is then interposed between the die and the counter, and swaged until it conforms perfectly to the face of the former, annealing the plate frequently to render it more pliant and manageable under the hammer. Unless the plate used is purer and thinner than is generally employed, or than is consistent with the required strength, it will fail to be forced perfectly into the groove around the chamber by the process of swaging alone ; a more definite border, however, may be formed by forcing the plate in at this place with a small, smooth-faced stamp, shaped to the angle of the groove, passing round the chamber and carefully forcing the plate in with the stamp and a small hammer or mallet until a somewhat sharp and abrupt angle is obtained to the palatal edge of the chamber. After the chamber is as perfectly formed as possible in this way, the plate should be well an- nealed and again swaged to correct any partial deformity occasioned by stamping the chamber. A still more perfectly defined angle may be given to the borders of the chamber in the following manner : After swag- ing the plate sufficiently to indicate the exact position and form of the chamber, the portion forming the latter should be separated from the main plate by completely dividing it aa ith a small, sharp, chisel-shaped instrument, cutting on a line with PARTIAL DENTURES HELD BY ATMOSPHERIC PRESSURE. 427 the groove around the chamber until the latter is entirely sepa- rated. The cut portion of the main plate is then trimmed evenly Avith a file, being careful not to enlarge the opening more than is required to remove the irregularities of the edge formed in cutting. The plate, with its central portion removed, is then placed upon the die, wdien a separate piece of gold cut to the general form of a chamber, but somewhat larger than the opening in the main plate, is adjusted over the chamber, and struck up with the plate until the overlapping portions of the central piece are forced down upon the plate around the margins of the chamber. It is not, however, always necessary to employ a separate piece of gold for the chamber, as the central portion cut from the plate in the first instance may be sufficiently enlarged for the purpose. This is accomplished by first flattening out the detached portion, annealing it, and then passing successive portions of its edges a sixteenth of an inch or more between the rollers, the latter being sufficiently ap- proximated to produce a perceptible thinning of the margins. A\ nen the entire border of the chamber piece has been thus attenuated and extended, it will be found so much enlarged that, when adjusted to the die and swaged in connection with the main plate, its borders will overlap and rest upon the margins of the opening in the base, as in the other case. The portions of the plate and cut chamber lying in contact are now coated with borax and pieces of solder placed along the line of union on the lingual side of the plate, when the twro pieces, being transferred to a bed of charcoal, are permanently united by flowing the solder with a blowpipe. Sufficient heat should be applied to induce an extension of the solder between the two portions of plate, filling up completely the gap between them to the edge of the orifice in the main plate, forming, at this point, a square and well-defined angle to the margins of the chamber. CHAPTER XL METHOD OF OBTAINING AN ANTAGONIZING MODEL FOR PARTIAL DENTURES ; SELECTING, ARRANGING, AND ANTAGONIZING THE TEETH J INVESTING, ADJUSTING STAYS, SOLDERING, ETC. Having constructed the plate or base to be used as a support for partial sets of teeth in either of the ways described in the preceding chapter, it Avill be necessary, before arranging the teeth on the plate, to secure an accurate representation of all the remaining natural teeth of both jaws in plaster, preserving accurately the relation which these organs bear to each other in the mouth. This is effected by what is called an antagonizing model, and may be secured in the following manner:— A roll or strip of adhesive wax is first attached to the lingual border of the plate, and its adhesion secured by holding the opposite side of the plate for a moment over the flame of a spirit-lamp. The wax used for articulating purposes should be harder and more tenacious than plain beeswax, and may be compounded from the following formula:— Beeswax,...................1 pound. Gum mastich,.................2 ounces. Spanish whiting,................1 ounce. The wax is first melted in a shallow vessel, and the mastich, finely pulverized, gradually added, and then the whiting, stir- ring constantly until thoroughly incorporated. The rim of wax being arranged on the plate, all superfluous portions overhang- ing the margins occupied by the remaining teeth are cut away; the plate may then be placed on the model and the wax again trimmed, leaving it somewhat fuller than the outer circle of the teeth, and from one to three lines longer than those immediately adjoining the spaces. The plate, with the wax attached, is then placed in its proper position in the mouth, and the patient in- structed to close the jaAvs naturally until the remaining teeth meet; one-third or more of the crowns of the opposing teeth 428 ANTAGONIZING MODEL FOR PARTIAL DENTURES. 420 opposite the spaces will thus be imbedded in the wax. A still fuller impression of the opposing teeth may be obtained, if desired, by pressing the edges of the wax down upon the crowns with the finger. If a series of anterior teeth are to be replaced, the mesial line of the mouth in front should be indicated upon the wax by drawing a line vertically across the latter to serve as a guide in the arrangement of the central incisors and ad- joining teeth. The plate and wax are then carefully removed from the mouth and again placed upon the plaster model, the latter having been previously obtained from an impresion of the parts Avith the plate in the mouth. The model is then placed on a slip of paper with the plate and wax upward, and the heel of the model extended from one to two inches poste- riorly to form an articulating surface for the remaining portion of the antagonizing model. The added portion of plaster may be confined by a narrow strip of wax or sheet-lead extending back upon each side of the model, into which a batter of plaster is poured to the depth of half or three-fourths of an inch. When hard, the edges and upper surface of the added plaster should be trimmed smooth, and a crucial groove, or two or three conical-shaped holes, cut in the surface of the latter to secure a fixed and definite relation of the two parts of the model. The articulating surface is then varnished and oiled to prevent the next portion of plaster from adhering; the imprints of the teeth in the Avax are also oiled. This portion of the antagonizing model, with the plate and wax attached, is exhibited in Fig. 345. The open space looking into the palatal vault should be closed with a sheet of softened wax to prevent the next portion of plaster from flowing into the cavity under- neath. A batter of plaster is now poured carefully upon the exposed surface of the wax, filling the imprints of the teeth perfectly, and extending back upon the heel of the model until it acquires a depth of half an inch or more. When sufficiently hard, the two sections of the model are separated, superfluous por- tions trimmed away, and the entire surface of both pieces glazed with varnish. The model complete, with the plate in place, and the wax (retained as a temporary support, whilst adjusting the artificial teeth) trimmed as required, are shown in Fig. 346 ; 430 MECHANICAL DENTISTRY. and if the manipulations have been accurate, this simple con- trivance will exhibit all the parts represented in plaster in pre- cisely the same relative position which they occupy in the mouth when the teeth are closed upon each other. It will be seen, by reference to Fig. 345, that only those teeth of the op- posing jaw which present to the spaces, are represented in plaster, as these are all that are required in arranging the teeth of replacement. Selecting, Arranging, and Antagonizing the Teeth.—The teeth of replacement should harmonize, as nearly as possible, in size, configuration, and color, with those remaining in the mouth; and when selecting teeth for any given case, the operator should be provided with a sufficient number of sample teeth to meet Fig. 345. Fig. 346. every requirement, by comparison, in respect of the various tints or delicate shades of color characteristic of the natural teeth and gums. The required size and form of the artificial teeth may be determined with tolerable accuracy by a compari- son with those on the plaster model, but the form or figure more certainly by a careful inspection of those in the mouth. Although .there are almost limitless varieties of manufactured teeth, both as respects form and color, it is not always possible, in partial cases, to obtain such as will harmonize with the natural teeth. As to form, a much closer resemblance to the natural organs in immediate relation with those of replacement can bs obtained by cutting away more or less freely from the SELECTING, ARRANGING, AND ANTAGONIZING THE TEETH. 431 cutting edges of the incisors, and the cusps of bicuspids and molars, in cases where the natural teeth are much worn. The ground surfaces may afterward be polished with pumice on a huff, and finished with rotten-stone and oil. The exigencies of practice, in respect of partial sets, will often require the re-shap- ing of ready-made teeth by grinding, and the original form should never be preserved at the sacrifice of utility and appear- ance. To secure harmony of color in the use of manufactured teeth as found in dental depots, is not always practicable. There are often conditions of the natural organs associated with decay and organic discolorations which it is impossible to match with porcelain teeth provided by manufacturers for general purposes. Such needs of the practitioner can only be adequately met by selecting a porcelain tooth, the body of Avhich is of the same general color as the natural organ to be matched, and treating it Avith mineral paints in imitation of the latter. These pig- ments may be obtained at any artist's furnishing house, and are such as are now very commonly used in porcelain painting. The process of painting and subsequent fusion of the pigment compound may be readily accomplished by any one of ordinary skill, taste, and judgment. The burning may be done in a muffle, using one of the small continuous-gum furnaces. In the absence of a furnace, a clean crucible may be used, treating the teeth to a full red heat in an ordinary fire; or they may be burned on a piece of charcoal with a blowpipe, using a naked flame. A moderate degree of heat, less than that required to melt silver, is sufficient to fuse the silicious compound with which the pigment is incorporated. Unless overheated, the mineral colors change very little in burning. By the means here indicated, almost any departure from the customary com- plexion of the natural tooth may be so closely imitated in the porcelain substitute as to defy detection. A more particular description of the expedient is described by Mr. William Dunn, Jr., in the British Journal of Dental Science. The practical im- portance of the process will justify its introduction here:— " The colors Avhich I generally use are: yellow, green, dark blue, brown, pink and black; all these colors are readily dis- 432 MECHANICAL DENTISTRY. solved by essence of turpentine or essence of mint, when with a fine camel's-hair pencil they may be blended in any combina- tions, and the surfaces, necks, tips or other parts painted, tinted, lined or otherwise made to perfectly coincide with any natural teeth however irregular or parti-colored they may be. Of course, in most instances it is necessary to grind or disfigure the artifi- cial teeth before painting them, and thus may be represented the worn-down teeth of advanced age which so frequently show the dark-brown tinted dentine within a circle of paler enamel, or the dark ring enamel with the light centre; the stained crowns of the bicuspids and molars under similar circumstances, the dark necks of denuded teeth, although the enamel surface may remain a good color, the blue-black appearance of carious teeth, either stained naturally or from amalgam stoppings. If naturally, it is very effective to grind notches out of the artifi- cial teeth to represent decay and stain Avithin and around the parts so disfigured. Honeycombed teeth may also be well represented by similar treatment. Indeed, there is practically no limit to the capabilities of the materials in skillful and artistic hands. " I find a white pallet advisable for mixing the colors. "After the teeth are painted they should be placed on pieces of platina or platina gauze, or in separate crucibles, for care should be taken that they do not touch one another. "If a whole set has to be colored, it Avill be found conve- nient to fix them in a row in a mixture of two parts of plaster-of-Paris and one part of fire-clay—which will not crack in firing. In this way a more uniform tint can be given than if done separately. " For firing, I prefer the handy and simple, but effective, little gas furnace invented by Mr. Verrier, in wdiich it takes about five minutes. The sufficiency of heat can easily be determined by watching until the crucible becomes a cherry red. Care must be taken not to overheat, otherwise the colors—especially the lighter ones—will disappear. These colors are as a general rule unalterable, but the operator must bear in mind that in passing through the vulcanizing process they are apt to become a little darker, and regulate his tints accordingly. At the same SELECTING AND ARRANGING THE TEETH. 433 time the darkness can be corrected, if necessary, by applying fine sandpaper or pumice powder. "With the pink color a very fair imitation of the gums can be produced; quite efficient, in most cases of a single tooth, to prevent that disagreeable and unsightly appearance so often seen, of a long tusk, rather than tooth, between two short teeth. " With a little attention and practice any one may soon mas- ter the initial difficulties of this painting work, and few, once having seen the advantage of the results, Avill again be con- tent with the old method of using the nearest color attainable." A greater or less change in the form of porcelain teeth will be required, in nearly all cases, in fitting them to the vacuities in the jaw; and this is more particularly so in those cases re- quiring the use of gum teeth. This alteration of form is effected by grinding away portions of the tooth upon an emery or cor- undum wheel, attached, as will be seen in Fig. 347, to a foot- lathe. If the edentulous portions of the ridge have suffered but little change of form by absorption, as Avhere the teeth have been recently extracted, and plate teeth (those representing only the croAvns of the natural organs) are used, the poste- rior portions of the base of the latter resting upon the margins of the plate will only require to be conformed to the irregulari- ties on the surface of the base-plate, grind- ing sufficiently to give to them the proper length and relative position, while their anterior cervical portion is permitted to overlap the edge of the plate and rest di- rectly upon the gum in front on a line with the adjoining teeth. When, however, a considerable concavity exists in the ridge and external border, and single gum teeth are employed to restore the customary fullness and contour of the parts, the gum portion of the tooth should be ground away on its posterior face sufficiently to restore the circle of the gum 28 434 MECHANICAL DENTISTRY. on the external border of the alveolus, and from the base of the tooth where it rests upon the plate, to admit of a proper rela- tive position of the artifi cial crowm; while those portions of the porcelain gum terminating at, and adjoining the remaining teeth, next the spaces, should be formed Avith a thin, retreating edge, where it laps upon the natural gum, giving to the parts, when the substitute is adjusted to the mouth, the appearance of an unbroken denture and a continuous gum. When the space to be supplied requires a series of two or more single gum teeth, the latter should be united to each other with the greatest care and exactness by grinding the proximate edges of the gum portions until the coaptation is such as to render the seams im- perceptible in the mouth. In adj.usting the porcelain teeth to the plate, the base of each tooth should be ground to rest as directly and uniformly on the plate as possible; for if thrown, in any degree, from the plate, the whole strain in mastication will come upon the platinum rivets, and, in a comparatively short time, the latter will either be entirely worn or cut off, or the artificial crown will be fractured on a line with the pins. In antagonizing partial sets of teeth, the indications pointed out by the customary closure of the natural organs should be followed as nearly as the form and position of the opposing teeth will permit. A changed or abnormal relation of the teeth of both jawrs, however, frequently renders it difficult to effect a satisfactory adjustment of the teeth of replacement. If, in the case of the bicuspids, for example, one or more teeth in the under jaw project into a vacuity above to the extent of one-third or more of its depth, a direct closure of the substituted organs upon these, in the ordinary manner, would be impracticable without a corresponding shortening of the porcelain teeth, enforcing, in such cases, an inharmonious arrangement, entirely inconsistent with the just requirements of the case. The diffi- culty cited, or any of the various modifications of it, may be overcome wholly, or in part, in one of two or three ways. If the teeth encroaching upon the opposite space are very loose, as is frequently the case with those that have become elongated from the long-continued want of an adequate opposing force, SELECTING AND ARRANGING THE TEETH. 435 or are hopelessly carious or otherwise diseased, they should be at once removed. If they remain firm and sound, and stand slightly within the circle of the teeth of the opposite jaw, or if they have somewhat of an inward inclination in the arch, the vacuity opposite may be filled with non-masticating teeth, as a canine, on the lingual side of which an antagonizing cusp of gold may be constructed, allowing the point of the cuspid to lap over upon the labial face of the encroaching tooth or teeth; or a bicuspid, manufactured for the purpose, with the inner cusp near the base of the tooth, may be used instead. Addi- tional room may be provided, in such cases, for the overlapping portion by filing away from a corresponding point on the op- posing tooth. If, however, taking the most impracticable case, the intruding teeth are sound and firm, and stand vertically in the arch, closing between the opposing teeth on a line with, or somewhat outside of, the outer circle of the latter (the elonga- tion of such teeth being rather relative than absolute, as Avhere it results from a mechanical wearing away of the remaining antagonizing teeth and a corresponding approximation of the jaws), the practitioner will be compelled either to submit to a mal-arrangement of the teeth of replacement by grinding away sufficiently from their grinding surfaces to permit an unob- structed closure of the natural organs, or decline the operation altogether. The undue projection of the teeth of one jaw into a vacuity occurring in the one opposite more frequently happens, however, in connection Avith the loss of the superior incisors. In such cases, the points of the lower incisors very frequently encroach upon the circle of the upper teeth, so that, when the artificial teeth are arranged above in correspondence with the circle of the adjoining teeth, and the jaA\\s are approximated, the points of the inferior teeth will strike prematurely either upon the cutting edges of those above or will close upon their inner sur- faces—impeding thereby, or entirely preventing, the occlusion of the teeth posterior to them. For such cases thin teeth should be selected, and, whenever necessary, the lower teeth may be filed aAvay sufficiently, while those of replacement should, at the same time, be arranged as prominently as the circle will 436 MECHANICAL DENTISTRY. admit of. If these expedients fail, and a sufficient number of teeth posterior to the incisors require to be substituted in con- nection with the same appliance, it will be better, in cases not susceptible of satisfactory correction by the means already sug- gested, to change the bite by substituting an entirely new antagonism with the artificial teeth—spreading the jaws suffi- ciently apart to relieve the artificial incisors in front. In no case, except that last described, should the artificial teeth come in contact with the opposing teeth before the occlu- sion of the remaining natural organs Avhen the jaws are closed. The contact of all the teeth of one jaw, artificial and natural, with those of the opposite, should either be simultaneous, or the natural teeth should be permitted to strike first. In view of the difficulties wmich so frequently present them- selves in connection with the arrangement of artificial teeth in partial cases, it may not be amiss to observe that, however essential to the natural and agreeable expression of the indi- vidual an exact and harmonious arrangement of the teeth of replacement may be, this requirement should, in some degree, be disregarded whenever the necessities of the patient, in respect of the comfort and utility of the appliance or the safety of the natural organs, demand it;—to what extent ap- pearances should be sacrificed to these considerations will depend upon the peculiar exigencies of the case, and cannot, therefore, be specifically stated. On the other hand, it may be observed that, if a sufficient number of the natural teeth are remaining in both jaws to enable the patient to perforin, with tolerable efficiency, the act of mastication, the mere utility of the substitute in regard to the performance of this function may be partly or wholly disregarded whenever there is suffi- cient reason to apprehend that the substituted organs cannot be antagonized with a view to the comminution of food with- out endangering the permanency and usefulness of the appli- ance by necessitating the application of forces unfavorably directed. Investing, Adjusting Stays, Soldering, and Finishing.—Having arranged and antagonized the teeth as accurately as possible on the plaster model, the piece should be placed in the mouth INVESTING, ADJUSTING STAYS, SOLDERING, ETC. 437 to detect and remedy any faultiness that may be found to exist either in the adaptation, position, or antagonism of the artificial teeth. It is then removed and imbedded in a mixture of plaster, sand, and asbestos, in the proportion of about two parts of the former and one part each of the latter. The body of the investient may be surrounded by a copper or sheet-iron band to prevent the plaster from breaking away whilst adjust- ing the stays or linings to the teeth.' All parts of the plate and teeth, except the lingual side of the former and the backs of the latter, should be incased in plaster to the depth of half an inch or more, and when the latter is sufficiently hard all traces of wax from the inside should be carefully detached with suitable instruments. The piece is now ready for the adjustment of stays or back- ings, which, when permanently united by soldering to the base and teeth, are designed to sustain the latter in position. These supports are formed from plate somewhat thicker than that used for the base ; a heavier and stronger stay being necessary Avhen they are not united laterally, as when plate teeth are used. If, however, single gum or block teeth are employed, and the stays are joined, forming a continuous band, plate one-half thicker than that used for the base will, ordinarily, impart adequate security to the attachment. A plain strip, corresponding in width with the tooth to be lined, is cut, and the end resting on the main plate conformed accurately with the file to the irregularities on the surface of the latter, and in such a manner as to permit the strip to take the direction of the tooth. The general form of the stay may, in the first place, be obtained by cutting a strip from a piece of gold with a pair of plate forceps. (Fig. 348.) The points upon the stay to be pierced for the admission of the platinum pins may be ascer- tained by coating the surface of the former with wax softened in the flame of a spirit-lamp, and pressing it first against the lower pin, the point of which will be indicated by an indenta- tion of the wax. The backing is then perforated at this point with a plate punch, two forms of which are exhibited in Fig. 349, one armed with a tongue, Avhich, when the plate is pierced, forces the latter from the punch. The strip is then re-applied 438 MECHANICAL DENTISTRY. to the upper pin, and the second hole obtained in like manner as the first. Instead of using wax, the ends of the rivets may be stained with some pigment, which will show the points to be pierced in the lining. Fig. 348. The stay should be adapted accurately to the face of the tooth; it is then cut to the proper length, reaching nearly or quite to the point of the tooth, and then shaped with a file to Fig. 349. the general form of the crown. When the stays are to be united they should be formed with a shoulder at a point cor- responding with the neck of the tooth, and the proximate INVESTING, ADJUSTING STAYS, SOLDERING, ETC. 439 edges below united closely by square edges, or the latter may be bevelled and made to lap upon each other. The process of soldering will be greatly facilitated and the piece will be more easily and artistically finished, by securing, in the first instance, a perfect coaptation of all the parts which are ultimately to be united. The sides of the holes in the stays facing the plate should now be enlarged or countersunk with a spear-shaped or conical bur drill, and when applied to the teeth the projecting ends of the platinum pins are cut off even with the backings and then split and spread apart with a small chisel-shaped instrument; a head Avill thus be formed to the rivets when solder is fused upon them, and which will prevent them from draAving from the linings. All the lines of union between the several pieces should next be well scraped, exposing a clean, bright, metallic surface to the solder; the seams are then smeared with borax, ground or rubbed in clean, soft water to about the con- sistence of cream;* after which small pieces of solder are placed along the joints and over the points of the platinum pins. The 'piece thus prepared is now placed in the furnace or ordinary fireplace in order to heat the entire mass throughout prepara- tory to soldering. The fuel most proper for this purpose is charcoal, either alone or combined with coke, the latter being preferable for the reason that charcoal alone is more quickly consumed, and burning away more rapidly underneath the piece is liable to drop to the bottom of the furnace. The fuel should be broken into small pieces and built up around the borders of the investient in order that all parts of the latter may be uniformly heated. The heating process should be con- ducted gradually, for if the piece to be soldered is subjected suddenly to a high heat, the plaster will be displaced by the too rapid evolution of vapor, and the integrity of the porcelain teeth will be endangered. The piece may be allowed to remain in the fire until the plate acquires a visible red heat, when it should be removed, placed on a suitable holder, and the solder * Slate is often used for this purpose, but is unfit, as in rubbing the borax loosened particles of the former become mixed with the latter and impede the flow of the solder, and becoming entangled render it unclean and porous. Ground glass or a porcelan slab is the best for the purpose. 440 MECHANICAL DENTISTRY. fused with the blowpipe. A broad, spreading flame should first be thrown over the entire surface of the plate and border of the plaster until the temperature of the entire mass is nearly that required to fuse the solder, and which is indicated by the latter settling and contracting upon itself; the flame may then be concentrated upon a particular point, as at the heel of the plate on one side, passing round from tooth to tooth until all parts are completely united and the solder is well and uniformly diffused. HaAring united the teeth to the plate, the piece may be allowed to cool gradually, or it may be plunged after the lapse of a few minutes into boiling water without risk of injury to the teeth. When cool, the plaster is removed and the plate placed in a solution of equal parts of sulphuric acid and water, where it may be allowed to remain until the discoloration of the plate and the remains of the vitrified borax, incident to soldering, are removed; or it may be put into a small copper vessel, partly filled with the same solution and boiled for a few minutes. After removing the plate from the acid, it should be boiled for five or ten minutes in a solution of chloride of soda or common' salt and water to remove thoroughly all traces of the former. Superfluous portions of solder are now to be removed, and this at first may be more quickly accomplished by the use of burs of various forms and sizes attached to a lathe. After the rougher and more redundant parts are thus cut away, any re- maining irregularities upon the surface may be further reduced with properly formed files, scrapers, and cutting instruments. Flat and half-round curved files, and scrapers having a right and left curvature to their cutting edges, and chisel-shaped cutting instruments for paring or chipping away (Fig. 350), are the implements usually employed for this purpose, and with which a comparatively smooth surface may be obtained; after which, the filed portions should be well rubbed with Scotch stone until all traces of file-marks or other scratches are com- pletely removed. With a rapidly revolving brush attached to a foot-lathe, the final polish or lustre may be imparted by the use, first, of Spanish whiting, or prepared chalk, and then rouge mixed with water or alcohol. The following method of finishing plate-work, communicated INVESTING, ADJUSTING STAYS, SOLDERING, ETC. 441 by Professor J. L. Suesserott,* embodies some practical sug- gestions in reference to this process: " The first step is to pro- cure and attach to the lathe a three- or four-pronged fork, or a screw such as is used for Avrthdrawing a load from a gun; upon this a good, smooth cork is fixed, and, with a sharp knife, turned to any desired shape. The cork is saturated with water as well as it can be, and powdered pumice placed upon it. If we have been careful to remove all excess of solder from our Avork, which can easily be done by a bur attached to the lathe, we can, with the cork and pumice, make a very smooth surface, and this can be still more perfectly accomplished by substitut- ing a very finely powdered spar for the pumice, after Ave have removed the largest scratches Avith the latter. By continuing Fig. 350. the cork for a little while after the above-named poAvders have heen used off, we avoid the use of the Scotch stone; and finally we dispense with the burnisher, by taking a new cork Avith a piece of chamois or buckskin stretched upon it, and going over the plate in the same manner as before, Avith the lathe revolving very rapidly. "A higher color can be given to the plate by the use of the burnisher after the above proceeding, but we can certainly not produce a smoother surface. " Some precaution is necessary by those who have never used the lathe in finishing the plate; in the first place, the careless * Erroneously ascribed in the first edition to Professor T. L. Buckingham. 442 MECHANICAL DENTISTRY. use of the bur, in removing the excess of solder, might result in the weakening of the piece by removing more than necessary, or, what would be still worse, holes might be cut entirely through the plate. Again, in polishing, if a little care is not taken, the fork or screw, whichever is used, may pass through the cork, and before the operator is aware he will have inflicted an injury that will be difficult to repair. A small amount of experience—that which is essential in the proper performance of every nice operation—will enable almost any one, even those to use a common expression, ' whose fingers are all thumbs,' to finish their work in about one-eighth of the time that the most expert workman would require for the accomplishment of the same by the old method." In the final adjustment of the finished piece to the mouth, and after any additional change in the form of the teeth neces- sary to secure the most perfect antagonism has been made, the patient should, in all cases of partial dentures, receive explicit directions in regard to the general care and management of the appliance and the remaining natural teeth. Ordinarily, there will be but little difficulty experienced by the patient in the immediate and successful use of a substitute supported in the mouth by clasps, or any equivalent means, but in the case of atmospheric-pressure plates, the patient should be candidly ad- vised of the probable want of stability incident to the first use of the appliance, and the consequent annoyance which in many cases follows its occasional displacement in mastication until such time as the adaptation of the several parts to each other are perfected, and the patient has acquired a habit of controlling and directing the forces applied to the substitute. The time necessary to accomplish these results will depend much upon the form and condition of the mouth, a favorable or unfavor- able antagonism, the adaptation of the plate, and the aptitude and temper of the patient. It will be prudent and but just to the patient to state that the complete utility of an appliance sustained by atmospheric pressure will not, probably, be realized in less time than from four to six weeks; and this estimate of time, in a majority of cases, will be fully justified by experience in the cases under consideration. INVESTING, ADJUSTING STAYS, SOLDERING, ETC. 443 The importance of thorough and absolute cleanliness of the substitute and remaining natural teeth, and the reasons there- for, should be clearly stated; and the comfort, utility, and dura- bility of the artificial fixture, as well as the safety of all the remaining natural organs will depend, in a great measure, upon the fidelity of the patient with respect to the observance of these injunctions. In those cases especially where clasps are used, the substitute should invariably be removed after each meal and cleansed, while the teeth clasped should, at the same time, be freed from deposits of food or other foreign substances with a brush, or any of the means usually recommended for the purpose. CHAPTER XII. ENTIRE DENTURES. Before proceeding to describe in detail the mechanical pro- cesses or manipulations concerned in the construction of entire dentures, unnecessary repetition will hereafter be avoided by first considering in this place certain underlying principles and fundamental requirements which are common to all the various distinct methods of replacement in edentulous cases. This preliminary treatment of the subject may be compre- hended under two general heads : 1. A consideration of the principles and attendant phenomena involved in the applica- tion of the forces commonly utilized as a means of attachment; and, 2. ^Esthetic requirements in the selection and arrange- ment of the teeth of replacement. A Consideration of the Principles and Attendant Phenomena Involved in the Application of the Forces Utilized as a Means of Attachment,—There are two forces in nature utilized in the retention of entire dentures, notably in upper cases,—Atmos- pheric Pressure and Adhesion, We shall consider, first, some of the attributes and phenomena characteristic of these forces, and then endeavor to make some practical application of them in elucidation of the subject in hand. Adhesion may be defined as the force by which the particles of different bodies stick together, in contra-distinction to cohe- sion, which is the force that holds the molecules of the same body together. There are a number of different kinds of ad- hesion, but our present purpose only contemplates those which relate to the adhesion of solids to solids, and fluids to solids. The adhesion of solids to solids is illustrated by pressing together two plates of glass or metal having perfect occluding surfaces, when they will be found to adhere with force enough to support not only the loAver plate, but some additional weight. Very delicate tests have been made by Avhich this adhesive force is accurately measured. An important practical fact, in 444 ENTIRE DENTURES. 445 this connection, has been well established, which has a direct bearing on the subject we are considering, namely, that the tenacity with which such plates adhere to each other is not in any manner due to, but wholly independent of, any force exerted by the pressure of the atmosphere, as was supposed by some of the earlier experimenters. The fact alluded to Avas conclusively proven by suspending the plates, the lower one of which was weighted, in the vacuum of an air-pump, in Avhich case the plates still remained adherent. Examples of this ad- hesive force as affecting solids might be almost indefinitely multiplied. The force of adhesion of solids to liquids is not less pro- nounced. When a polished plate is suspended on a delicately constructed balance, and brought carefully down on the surface of a liquid, completely excluding the air, adhesion will take place, the force of which will be modified by the kind of liquid in contact with the plate. It has been ascertained by careful experiment that the adhesive force of a polished plate of agate, one inch in diameter, in contact with water, is 25 grains; sul- phuric acid, 29 ; hydrochloric acid, 25; solution of saltpetre, 23; of lime, 21; almond oil, 16; petroleum, 16; turpentine and alcohol, 15; ether, 10. Where, as often happens, drops of the liquid adhere to the plate when separated, it proves that the adhesion of the liquid to the solid is stronger than the cohesion of the liquid itself, and that the numbers obtained in these experiments express rather the cohesion of particles of the liquid which were separated by the weight, than the adhesion of the plate to the liquid. As in the case of adhesion of solids to solids, it Avas formerly claimed by some that adhesion in these cases was due to atmospheric pressure, but that was dis- proved in the same manner as the other. Perfect exclusion of air is essential to the operation of this force, a suggestive fact in connection with the adaptation and retention of entire den- tures. Atmospheric Pressure is that force exerted by the air by reason of its gravity, one of its mechanical properties being weight, which renders it amenable to the same law of attraction that affects all other bodies similarly endowed. It exerts a pressure 446 MECHANICAL DENTISTRY. not only downward, but according to the law of fluids, sideways, upward, etc., as by the mobility of fluid particles any pressure is transmitted in all directions. Superadded to gravity is its elastic force, a property which, like all gaseous bodies, it pos- sesses in a remarkable degree. This property is familiarly demonstrated by filling a bladder with air, and exposing it to rarified air at a great height. The external pressure of the atmosphere at such an altitude being diminished, the air within tends to expand to the same degree of rarity as that Avithout, and with such force as to burst the bladder. The partial dis- placement of air by compression within a diving-bell by the pressure of water at a low depth, and the forcible expulsion of the intruding water as the bell is brought to the surface, not only illustrates its elasticit}^, but its impenetrability also, or its property of preventing another body from occupying the space where it is. There are many other examples of the pressure of the atmosphere and the force exerted by virtue of its elastic property, but those of most interest and consequence to the prosthetic specialist relate to their effects on the human organism. It is estimated that the force exerted by the pressure of the atmosphere on the body of a medium-sized man must be about fifteen tons, a force sufficient to crush and destroy him if applied only to the external portions of the body. Such pres- sure, however, is neutralized and rendered harmless by counter- pressure from within; a result due to the elasticity of the air which exerts a force everywhere and in all directions alike, from the external parts inwardly, and from those within outward. The tendency in nature everywhere is toward the establishment of an equilibrium of atmospheric pressure, and when these balanced forces are disturbed, unusual and characteristic phe- nomena follow. If, as in the case of " cupping," the external pressure of the atmosphere is removed by the formation of a vacuum, the elastic force of the air operating from Avithin, and meeting no counter-force at the point cupped, will, by virtue of its inherent elastic energy, force the soft tissues into the body of the cup as the result of this tendency to an equilibrium. The latter occurs as soon as the unoccupied space forming the vacuum is filled with the tissues, when, the accustomed balance ENTIRE DENTURES. 447 of forces being restored, the cup will loosen and fall off. If the disturbance of the equilibrium of forces acting from without and Avithin is general, as in the case of an aeronaut in a balloon at great heights, the result of this tendency may, and often has, put life in jeopardy by expansion of the internal organs. On the contrary, the body exposed to greatly increased external pressure of the air, as when the latter is condensed in the diving- bell at low depths, or in caissons employed in forming a foun- dation of subaqueous structures, the results may be equally harmful or fatal by compression of the internal organs. Let us now make some brief application of the above well- established facts in explanation of the manner in which atmos- pheric pressure and adhesion act as forces in the retention of so-called "Atmospheric-Pressure Plates," and the phenomena and results of such action. This discussion may be premised with the statement of the general proposition that, in the case of entire dentures, retention of the plate in place by atmospheric pressure pre-supposes a vacuum obtained by exhaustion of the air from a cavity, of what- ever form, located somewhere between the plate and the mucous surfaces on which the latter rests, and that such cavity implies space. Whenever, therefore, a dental appliance of the kind under consideration is in uniform contact at all points with the parts in the mouth, it is manifestly improper to speak of it as being held in place by atmospheric pressure, or to designate it as an " atmospheric-pressure plate." Uniform contact implies perfect continuity between the plate and the parts on which it rests, and this necessarily precludes the idea of space, and with- out space a vacuum is impossible, and in the absence of the latter, the atmosphere, as we shall endeavor to shoAv, is wholly inoperative as a retaining force. To comprehend the matter intel- ligently, we must not lose sight of the important central fact that the atmosphere, in its undisturbed condition, exerts an equal pressure in all directions, a property largely due to its elasticity, and that in obedience to this laAv, in its operation upon the human organism, the force exerted from without inward is exactly counterbalanced by the same force acting from within outward, thus establishing an equilibrium of the counteracting 448 MECHANICAL DENTISTRY. forces, and a consequent neutralizing of pressure at the surface. This equalized force is an essential condition of human well- being and of human life, as has been heretofore stated and demonstrated by examples. The absurdity, therefore, of attrib- uting the retention of substitutes, adapted in this manner to the mouth, to the pressure of the atmosphere is apparent. There can be no reasonable question but that substitutes so applied are held in situ by that force manifesting itself in Adhesion. In all cases where the plate or other base is accu- rately adapted to the entire mucous surfaces, and the air thoroughly excluded, the essential condition favoring its reten- tion by adhesion is secured, namely, perfect contact of a solid with the fluids with which the mucous surfaces are constantly bathed. Let us now consider, as briefly as possible, the manner in which air-pressure acts as a retaining force when applied to cavity-plates, and in the same connection some of the phe- nomena resulting from such action. When a plate, provided with a cavity or chamber, is applied to the mouth, two concurrent phenomena are observed—the immediate and forcible attachment of the plate to the mucous surfaces, and the obtrusion of the soft tissues into the space from which the air has been exhausted. The first is due to the external pressure of the atmosphere, the latter to the same force acting from within. Here, again, it is essential to remember the fundamental fact that atmospheric pressure acts equally in all directions. In the case of the human body, as before stated, the pressure of the air from without inwardly is exactly counter- balanced by the pressure of the atmosphere within outwardly, establishing in this manner an exact equilibrium of forces, the one neutralizing the other at the surface. The phenomena to which attention has been called, in the case of an applied cavity-plate, are the result of a disturbance of these ordinarily balanced forces. When a vacuum, partial or complete, is formed by exhaustion of air from the chamber, the external pressure of the air, meeting with a diminished counter-resist- ance from within, by reason of the vacuum, forces the plate against the parts, while at the same time the atmospheric pres- ENTIRE DENTURES. 449 sure acting from within outwardly, meeting with a like dimin- ished resistance at the surface embraced within the limits of the chamber, forces the soft tissues into the chamber. Thus avc find displayed the universal tendency to an equilibrium of atmospheric pressure, and a practical illustration of nature's proverbial abhorrence of a vacuum. It is not probable that a perfect vacuum is ever secured by the means ordinarily employed by the patient, unless, perhaps, in the case of very shallow cavities. The moment any portion of the contained air is exhausted, there is instant and forcible pressure of the plate upon the soft tissues immediately sur- rounding the chamber, acting as an effectual mechanical im- pediment to farther egress of air. The power to exhaust is therefore self-limited, and a partial Aracuum only the result. Sooner or later, in a large percentage of cases, even this limited power is rendered inadequate to secure any degree of exhaus- tion by the intrusion of tissues which, by long-continued and unrelieved pressure, become in time permanently hyper- trophied. The completeness with which the chamber may become filled with soft tissues will depend partly upon the form of the cavity, and partly upon the abundance and mobility of the tissues. If the cavity is constructed with vertical walls, and sharply-defined margins, the latter, by becoming quickly im- bedded, will act as a mechanical obstruction to any ready, sliding movement of the tissues into the chamber. Plates so constructed adhere with greater tenacity and more persistency, especially when the parts embraced are rigid and immobile; but it is at the cost of the maximum of injury which cavity plates are capable of inflicting, and Avhich is often, in extreme cases, characterized by rupture of the superficial vessels, wound- ing of the mucous membrane, and in active inflammatory con- ditions which not unfrequently involve the adjacent tissues. More ready entrance of the tissues into the chamber occurs where the edges of the latter are rounded and the walls slope toward the centre, as in the case of those that are swaged, but this form is at the expense of the retaining force, since atmos- pheric pressure from Avithout is always diminished in propor- 29 450 MECHANICAL DENTISTRY. tion as the cavity becomes filled in with the tissues, and ceases entirely when a vacuum no longer exists. The facility with which the chamber will become occupied is greatly increased when the soft tissues are in excess, their softness and mobility offering but a feeble resistance to the atmospheric pressure from within, in which case the cavity soon becomes partly or wholly occupied by them, and what retaining force was originally secured by atmospheric pressure will, in a comparatiA^ely short time, become greatly impaired or wholly inoperative. In addition to the force acting from within, tending to weaken the attachment of a cavity plate by filling in the chamber Avith soft tissues, there is another force, acting mechanically, which contributes in no inconsiderable degree to the same result. On exhaustion of the air from the chamber, the plate being pressed with considerable force against the mucous surfaces will exert a corresponding pressure upon the tissues immediately sur- rounding the chamber, the mobility of which admits of more or less displacement, and as this always occurs in the direction of the least resistance, they readily enter the cavity. When it is remembered how inadequate and transitory are the uses of so-called " air-chambers," and how capable, under ordinary circumstances, they are of inflicting serious and per- manent injury upon the delicate tissues of the mouth, there would seem to be no sufficient reason or justification for their employment, except possibly in rare and exceptional cases. Experience has amply demonstrated that equally secure and much more enduring attachment of the substitute may be ob- tained in the utilization of adhesive force alone—a means of retention wholly exempt from the harmful consequences that too often follow the application of atmospheric pressure conse- quent on the formation of a vacuum. There are, however, many cases where spaces or cavities may be employed to advantage for the purpose of securing, through the temporary pressure of the atmosphere, increased stability of a dental appliance subjected to the forces applied in mastication. There are associated conditions of the mouth which, in their normal and undisturbed relation to each other, prevent, to some extent, a uniform or equalized bearing of the substitute upon ENTIRE DENTURES. 451 the parts to which it is applied. These conditions relate to unequal hardness and softness of the tissues, and a consequent inequality of resistance to pressure. Thus, if the ridge is rela- tively softer and more compressible than the central portion of the arch, the plate, when force is applied over the ridge, will " ride" upon the central portion, as upon a pivot-point, and thus raise or detach the plate from the ridge on the opposite side. This is called " rocking" of the plate, the action being illustrated in the sport familiarly known as "see-sawing." The remedy for this consists in securing a space between the central portion of the roof of the mouth and the corresponding portions of the plate, so that when the substitute is applied to the mouth and the air exhausted, the greatest pressure will be expended upon the ridge, and, by compression, equalize the resistance. This space, Avhen the plastic vegetable bases are used, is obtained by scraping away from the impression at the . required points; raising the central portions of the plaster model with sheet-lead of proper form and thickness; or by trimming away from the palatal surface of the finished piece. In the case of swraged plates, the shrinkage of the metallic die Avill ordinarily afford the required space. In cases Avhere there is approximate uniformity of hardness of the ridge and central line of the arch extending antero-pos- teriorly, associated with soft and yielding tissues filling the fosses on either side and extending some distance up the lateral walls of the arch, it is customary, in order to equalize the pres- sure of the plate, or, rather, to secure uniformity of resistance to such pressure, to scrape away from such portions of the plas- ter model as correspond with the softer tissues, thus securing in the finished piece an increased convexity or fullness which, on application of the substitute, exerts a compressing force at such points superadded to that obtained either by atmospheric pres- sure or adhesion. It may be reasonably objected to this mode of procedure that the augmented compressing force thus ap- plied, being continually antagonized by the inherent elastic force of the tissue pressed, must inevitably tend to weaken the attachment of the substitute, and that such repelling force will (•ontinue to act, in a diminishing degree no doubt, until, from 452 MECHANICAL DENTISTRY. long-continued pressure, such of the tissues as are not displaced will become absorbed or atrophied. The objection is empha- sized by the further fact that, in such cases, the absorption is always preceded and accompanied by forcible displacement of superabundant tissue into the soft palate, inducing more or less irritation and ultimate chronic tumefaction of the displaced tissue at the posterior margin of the plate. The prevalent fal- lacy that the tissues thus subjected to pressure are condensed thereby has been considered in the initial portion of the chap- ter on impressions. No device will, we believe, so effectually and satisfactorily fulfill the requirements of the cases last mentioned as the one that provides for displacement of the tissues within the limits of the plate itself. This may be done by securing a graduated space including a large part of the palatal vault. This space should not be in the form of a cavity with defined walls, but should slope gradually toward the periphery in such manner that its boundaries shall be undistinguishable. By a graduated cavity is meant that, wherever the soft tissues are in excess, there should be a corresponding depth of space to provide for such varying degrees of displacement as are essential in the procurement of an equalized resistance to the pressure of the plate. By this method, there is not only no injury or objec- tionable deformity inflicted, but the attachment of the substitute, instead of being impaired as in the other method, is maintained at first by the full and unobstructed force of atmospheric pres- sure, and when, finally, the required displacement of tissue is accomplished by a filling in of the space, the best practicable adaptation is obtained, and the future stability of the substitute as perfectly provided for as is possible with the resources at our command. JEsthetic Requirements in the Selection and Arrangement of the Teeth of Replacement.—In selecting teeth for an entire upper and lower denture, the special requirements in respect of size, form, and color, will depend in a great measure upon the com- plexion, age, sex, general configuration of the face, etc., of the patient. Every separate denture, therefore, that is constructed in strict conformity with a faithful interpretation of the special ENTIRE DENTURES. 453 requirements of each individual case, will be characterized by shades of differences in color, form, size and arrangement of the teeth of replacement. The indication in the fulfillment of such requirements, broadly stated, is, that such selection of the teeth, in any given case, should be made as will, when suitably arranged, most perfectly reproduce the lost proportions of the facial contour, and restore the characteristic expression of the individual. To accomplish this with fidelity will require a higher order of intelligent discrimination, and a broader art culture than is required in cases where the operator is aided by comparison of the artificial with remaining natural teeth, as in partial den- tures. In the present case he has no resources except those that come to him through a critical and conscientious study of the laws of harmony as displayed in the typical forms of den- tures associated Avith individual physiognomy and tempera- ment. Says a thoughtful writer: * " We find that the necessity for art in dentistry exists in proportion to the hopelessness of the case. The greater the amount of lost tissue to be replaced, the greater the knowledge of natural form required to properly effect its replacement. Beginning with the restoration of por- tions of teeth through gold fillings, we come to the loss of the entire crown, and, finally, to that last resort, the replacement of the entire denture. Knowledge of form and color, of expression, character, and effect, now becomes imperative to the dentist. To relieve the condition of his patient, the art of the sculptor and colorist must be studied with more care than many of us are wont to give it, while a knowledge of temperament and physiognomy becomes an important element in our work." " No matter how anatomically correct," observes one of the most intelligent contributors to the literature of aesthetic den- tistry,f " or how skillfully adapted for speech and mastication, an artificial denture may be, yet, if it bear not the relation demanded by age, temperament, facial contour, etc., it cannot be otherwise than that its artificiality will be apparent to every beholder. *Dr. Eben M. Flagg, Dental Cosmos, March, 1881. fThe Teeth, by Dr. J. W. White. 454 MECHANICAL DENTISTRY. " This law of correlation, harmony, running through nature, attracts and enchants us by an infinite diversity of manifesta- tions ; the failure to recognize its demands by art is correspond- ingly abhorrent to our sensibilities. " In the social gathering, a lady who appreciates the law of harmony delights the eye by the taste displayed in her attire; another, though more elaborately and expensively adorned, yet failing to harmonize the details of her costume, attracts atten- tion only by the impression of incongruity. We hear fre- quently from a lady who is selecting a bonnet, or from a gen- tleman purchasing a hat or other article of wearing apparel, the question to a friend, does this become me ? the query indi- cating the recognition that, however exquisite the material, or excellent the manufacture of the article, a certain law of fitness prevails, the failure to comply with which makes the wearer appear ridiculous. We meet in the street one the color of whose hair we expect, by the law of association, to be fair, or sandy, and if otherwise, a wig or a dye is instantly suggested. " There is a relation between the physical form and the voice, from which we are led to infer in advance the character of the tones which from any given individual may be expected. This law of association in any case, having led us to anticipate a bass voice, the anomaly, should a falsetto greet us, is almost ludi- crous. " There is a similar relation between other physical character- istics and the teeth. A broad, square face, or an oval; a large, coarse-featured man, or a delicately-organized woman; a miss of eighteen or a matron of fifty; a brunette or a blonde,—these and other varieties present as many differing types, with teeth, in size, shape, color, density, etc., corresponding. If, then, teeth correlated in their characteristics to those which nature assigns to one class be inserted in the mouth of one whose physical organization demands a different order, the effect cannot be otherwise than displeasing to the eye, whether the observer be skilled in perception, or intuitively recognizes inharmony with- out understanding the cause." Written or verbal instructions can do little more than present general principles governing the selection of teeth for any given THE FOUR BASAL TEMPERAMENTS AND THEIR GENERAL INDICATIONS I BILIOUS. I INDICATIONS. SANGUINEOUS. 1 General Form or Framework NERVOUS. LYMPHATIC. 2 General Movement 3 Muscular Development Chest or Thorax Voice, Quality of . . . Complexion and Skin built. Tall, angular, massive; square' f",11. flnnly-rounded 9°n,0"r Delicate; slight, but erect and , ' e ' ' ^ development; medium height; ., ,. . runny, ueavj , uum.j. i.,.i,..., well-proportioned. Rapid but fitful in movements; Unsteady; uncertain; loose- quick in the sense of frequent, jointed ; sluggish ; deliberate. Well-defined; light, but sin-' Large, but flabby and ill de- Steady and persistent, Knotty; prominent; hard; tense; well-developed. Square and capacious; good expansive power. Strong, but inclined to harsh- ness. Favorable Endowments or Ad- vantageous Indications. Unfavorable Endowments or Dis- advantageous Indications . . Cranial Contour 10 | Facial Contour 11 Hair....... Eyes. Eyebrows Nose . . . Lips . . . . Brownish-yellow; tense, and inclined to roughness; dry. Strength ; endurance ; forti- tude ; decision; firmness. Inclined to melancholy; des- pondent. Square forehead and cranium. Angular; high cheek-bones. Full, graceful, and easy. Well-rounded and graceful. Well-rounded and capacious; deep and full. Smooth; sonorous; full. Florid; smooth; warm and dry. Hopeful; enthusiastic ; aspir- ing. Lack of self-control; impetu- ous. ewy. fined. Not broad but prominent; Large, but lacking in expan- very expansive. Isive power. Not very strong, but clear,; Poor in vibration, but often penetrating and ringing. Abounding in grayish tints; fiDe in texture, and elastic. Remarkable recuperative power. Mental fitfulness.and inclined to rapid degeneration or retro- gression. soothing and quieting in quality. Pallid; muddy; moist and cold. Rounding and full forehead! Cranium inclined to prepon- and cranium. derate over face. Round and full. Black, and closely curling; in- clined to coarse. Average size; black, and strong in expression. Golden to light chestnut; slightly wavy. Large; full; clear ; round; blue. Heavy; strong and straightly Fairly arched; not well- marked, marked. Strong in outline; Roman. Straight and shapely. Large, and brownish-purple. | Ruddy and full, Delicately oval. Brown; wavy; fine. Gift of self-control; calm; cool; quiet. Inertia; low recuperative power in pathological condi- tions. Forehead low and not shapely; often receding and flat. Flat-faced. Above average in size; dark brown; perceptive in expression. Well-marked and arched; fine- ly penciled. Finely cut and often delicately aquiline in form. Coarse; straight; drab, and sparse. Small, expressionless, and grayish. Sparse and indistinct. Flat; alse heavy. Fine and grayish-pink. Large, but not shapely, and pale. THE TEETH AS INDICATED BY TEMPERAMENT. GENERAL DIVISIONS. BILIOUS. SANGUINEOUS. NERVOUS. LYMPHATIC. General Color and Quality of Color . . Bronze-yellow, with strength or power of coloring. Cream-yellow, and inclined to translucency. Pearl-blue or gray; inolined to transparency. Pallid and opaque, or muddy in coloring. General Form .... Large and inclined to angular; rather long in proportion to breadth. Well proportioned; abounding in curved or rounded outlines ; cusps rounding. Length predominating over breadth; fine, long cutting edges and cusps. Large, but not shapely; breadth predominating over length; cusps poorly defined. Surfaces of the Teeth Inclined to transverse ridges, and abounding in strong lines; neither brilliancy nor transparency of sur-face, but slight translucency. Smooth, or nearly so; elevations and depressions rounded; cutting edges and cusps translucent. Fair degree ot brilliancy. Brilliant and transparent depres-sions and elevations; abounding in long curves. Surfaces of incisors devoid of de-pressions or elevations; opaque and dead in finish, even to cutting edges. Firm and close; well locked. Moderately firm; jaw inclined to rotate in mastication. Very loDg and penetrating. Loose and flat. Gum Margin or Fes- Heavy and firm, but inclined to angularity. Round and full, as regards both breadth and aepth. Delicate, shapely and fine; oval in curve. Thick and undefined in shape. Heavy and rugged in shape; squarely set. Numerous and graceful in outline; not heavy, but well rounded. Close, not numerous; small and long. Sparse and flat. ENTIRE DENTURES. 457 case. The completeness with which the requirements of indi- vidual cases are fulfilled will depend largely upon the operator's art intuitions, and his ability to properly interpret and apply the basal facts which an intelligent study of the relation of physiognomy and temperament to the teeth has revealed. The relations of the latter to the teeth have been clearly and fully set forth in tabulated form by Dr. J. Foster Flagg, which we herewith append. The first table relates to the basal tempera- ments, namely, bilious, sanguineous, nervous, and lymphatic, and their general indications; the second, to the teeth as indi- cated by temperament. A careful study of these tables, the subject-matter of which is by far the most valuable contribution that has yet appeared in connection with the subject under consideration, will furnish whoever avails himself of its practical suggestions a helpful means of solving one of the most difficult problems in pros- thetic practice. The following editorial, by Dr. White, on " Temperament in Relation to the Teeth," suggested, doubtless, by Dr. Flagg's tables, embodies not only a discussion of the general subject of temperaments, but some forcible and striking commentaries on the importance and value, aesthetically considered, of the indi- cations furnished by temperamental characteristics in the intel- ligent choice of artificial substitutes for special cases. The importance of the subject to which the article relates will justify its introduction here without abridgment:— " The animal creation is divided into kingdoms, sub-king- doms, classes, orders, families, genera, species. A further or sub-division includes in minor groups individuals whose salient I characteristics are correspondent or similar. Thus every living creature has certain physical peculiarities by which its position in this classification is determined. Man, as the head of the animal kingdom, besides having his place in this general scale, is distinguished by a still finer classification under the denomi- nation of temperament—an association of several distinguishing characteristics, such as size and form of body, complexion, color of the eyes and hair, and to a certain extent the disposition and character of the individual. 458 MECHANICAL DENTISTRY. " Temperament may be defined as a constitutional organiza- tion, depending primarily upon heredity—national or ancestral —and consisting chiefly in a certain relative proportion of the mechanical, nutritive, and nervous systems, and the relative energy of the various functions of the body—the reciprocal action of the digestive, respiratory, circulatory, and nervous systems. The stomach, liver, lungs, heart, and brain—digestion, assimilation, respiration, circulation, and innervation—are all factors in the differentiation of temperament; and according to the congenital predominance of one or the other, and the rela- tive activity of these functions, is the modification of the char- acteristics of the individual which assigns him to one or other of the basal or mixed temperaments. Each temperament is the result as well as the indication of the preponderance of one or another of these systems, and of relative functional activity. "A perfect equilibrium of the different systems is rarely, if ever, presented in any individual. One having a balance of all the temperaments would be temperamentless, or of no special temperament. It is difficult, in some cases, to decide positively to which variety a special case belongs, the several temperaments being combined and blended in such ever-varying proportions. Not infrequently the indications are even contradictory, and the^ blending of several temperaments requires a nice discrimina- tion to define the admixture. The primary elements of tem- perament are susceptible of such manifold combinations; the determining forces are so complex, and our knowledge of their comparative values is so limited, that no rule can be given which will not fail in numerous instances to apply in all respects to individual cases; but that there is a general relation between constitutional qualities and external signs does not admit of question. " Temperaments are readily divisible into four basal classes- bilious, sanguineous, nervous, and lymphatic; then again into sub-classes of mixed temperaments—a combination of two or more of the primary divisions. In these combinations one or other of the so-called basal temperaments predominates, and a compound term is used to express the complexity, as, for in- stance, the nervo-bilious, signifying that the bilious base—the ENTIRE DENTURES. 459 foundation temperament—is-qualified by an admixture of the nervous element, and so throughout the series. Twelve varie- ties of temperament, in addition to the four basal, may thus be designated by the combination in pairs of the original four. The admixture of the peculiarities of three or of all four of the basal temperaments results in what are denominated respect- ively ternary and quarternary combinations, which call for nice discrimination in diagnosis; but even such complexities are registered in the size, form, and color of the dental organs. " The value of a practical application of the study of tempera- ment in the practice of dentistry is apparent. That the rela- tion of the teeth to temperament is as a rule ignored by those engaged in prosthetic dentistry is evident in the mouths of a majority of those who are so unfortunate as to be under the necessity of wearing substitutes for lost natural dentures. "A certain law of harmony in nature between the teeth and other physical characteristics necessitates respect to size, shape, color, and other qualities in an artificial denture, in order that it shall correspond with other indications of temperament; and if teeth correlated in their characteristics to those which nature assigns to one temperament be inserted in the mouth of one whose physical organization demands a different type, the effect is abhorrent. The artificiality of artificial teeth is the subject of remark by those who have little or no conception of the reason therefor—simply an instinctive appreciation of the in- congruity and unreality. It is indeed rare to see a case in which there is occasion for a moment's hesitation as to the fact of replacement. There is no dental service that, from the [esthetic stand-point, is, as a rule, so illy performed as the pros- thetic. Thousands of dentures are constructed which serve the needs of the wearer for speech and mastication, but which are nevertheless deserving of utter condemnation as art productions. More attention has been paid to the best methods of restoring impaired function—securing comfort and usefulness in artificial dentures—than to a correlation of the substitutes to the physi- cal characteristics of the patient. " What is needed is such an appreciation of the law of cor- respondence that the dentist can cipher out, as by the rule of 460 MECHANICAL DENTISTRY. three, the character of teeth required in the case of an edentu- lous mouth, with the same precision as the comparative anato- mist can from a single bone indicate the anatomical structure of the animal to which it belonged. The probability is that in many, perhaps in most, of the cases of incongruous artificial dentures the fault is not in carelessness or indifference of the dentist, but in failure to recognize the requirements of tempera- ment. A certain family resemblance to each other in a set of teeth is considered essential, but the adaptability of the set as a whole to a given case should be esteemed of even greater im- portance. Especially is there a notable failure to recognize the color demanded by form. A set of teeth in which not only the relative length and breadth, but every line and curve character- ize it as belonging to a certain temperament, is, in contravention of every law of correspondence, made of a color which was never found in nature associated with such forms. Thus we see constantly such incongruities as the association of the mas- sive tooth of the bilious temperament with the pearl-blue color belonging to the nervous temperament, and the long narrow teeth of the nervous temperament of the bronze-yellow color never seen in the mouths of any but those of a bilious tem- perament. " The trouble is not with the manufacturers; they supply the demand. The fact is, the requirements of the law of corre- spondence have not been sufficiently studied by the profession. The first study of the dentist who aspires to the dignity of artist, when proposing to replace a lost denture, should be how to restore the natural appearance of his patient, and this can only be effected through an appreciation and observance of the temperamental characteristics and the law of correspondence or harmony. Age and sex may somewhat modify the require- ments in a given case, but the basal fact on which he should proceed is temperament. A failure to recognize its demands will result in failure—from an aesthetic stand-point. A knowl- edge of the distinguishing characteristics of the various tem- peraments and the style of teeth which conform to nature's type in the physical organization marks the difference between the dental mechanic and the dental artist." ENTIRE DENTURES. 461 The fulfillment of the highest art conceptions in the construc- tion of entire dentures is far from being complete with the mere selection of teeth in conformity with temperamental and other indications. This essential preliminary step is concerned chiefly with the form and color of substitutes, but the highest attainments in the art of replacement can never be attained without an intelligent perception of the aesthetic requirements which have inseparable relation to the arrangement of the teeth Fig. 351. selected in strict conformity with the same law of harmony or correspondence that applies to form and color. The art of arrangement is scarcely less difficult, and certainly not less im- portant, than the art of selection, and equal judgment and dis- crimination will be required to effect such an adjustment of the teeth as will most faithfully serve to restore the facial contour and characteristic expression of the individual. This will, in 462 MECHANICAL DENTISTRY. most cases, necessitate some deviation from that uniformly symmetrical or ideal relation of the teeth to each other charac- teristic of perfect regularity of arrangement, and which rarely exists except in connection with a perfectly balanced develop- ment of the jaws and teeth, a condition which may be said to be almost phenomenal. Such an arrangement is exhibited in Fig. 351. The kind or degree of displacement of any particular tooth or teeth to effect such irregularity of arrangement as would best reproduce the customary expression of the individual in any given case, cannot, of course, be here indicated. The operator is necessarily thrown upon his own resources in deter- mining, in this respect, the necessities of individual cases. Generally speaking, the changed relation of the teeth is, in most part, confined to the six anterior teeth, above and below, as they are most largely concerned in expression; but it may often be extended to the bicuspids and molars, which may be displaced within or without the arch, or given an oblique posi- tion, with here and there interdental spaces, some of which may be wide enough to suggest the loss of the natural teeth at intervals. The central incisors may be made to overlap each other, with the laterals in normal position; or the latter may be given a position inside of the circle, which will give a rela- tive prominence to the centrals and cuspids, or they may be partially rotated while retaining their regular position in the arch, or be made to overlap or underlap the centrals, in which case the latter may be made to diverge somewhat from each other at the points, leaving some space between them. There is scarcely any limit to the capability of effecting malpositions of the teeth of replacement, and this is especially true of those forms of substitution known as continuous-gum work, and in the use of celluloid, either process, by admitting of the use of single, plain teeth, affording unlimited opportu- nities for the optional placement of the teeth. In the use of sectional gum teeth, all the usual forms of dental irregularity have been faithfully reproduced by manufacturers, and, when selected with an intelligent apprehension of their fitness for any particular case, will meet all ordinary wants of the practi- ENTIRE DENTURES. 463 tioner in the use of rubber, or a metallic plate-base with rubber or celluloid attachment. The minimum of capability in effecting irregularity of arrangement attaches to soldered work, where, as is usually the case, single gum teeth are employed. It is possible often, when teeth have been selected conforming as nearly as practicable to the requirements of the case in color, to so change the form of the teeth by judicious grinding of the proximate surfaces, cutting edges of the incisors, and the points of the cuspids, and occluding surfaces of bicuspids and molars, as to greatly change the effect in the mouth, giving them an harmonious expression impossible in the use of manufactured teeth in their unchanged form. This is particularly observable when they are ground in imitation of the partial destruction of the occluding surfaces by erosion, a condition very commonly associated with middle age. The effect is still farther enhanced by coloring the portions of the ground surfaces in imitation of the dark discoloration usually associated with exposed dentine. This may be readily done in the manner described in the chapter on partial dentures mounted on metallic plate-base. The same process of coloring may also be applied to single por- celain teeth representing absorption or recession of the gum at the cervix, which is always of a darker hue than the crown. An additional device, sometimes employed to disguise the fact of artificiality, is that of introducing gold fillings into one or more of the front teeth. Cavities for this purpose are some- times formed in porcelain teeth at the time of baking. When these are not readily procured, the operator may easily impro- vise them. A dovetailed slot may be ground in the proximate side of a front tooth with suitably formed corundum disks, or a concave depression made and retaining pits formed with a hard-tempered steel drill. A correspondent of the Cosmos gives the following method of using the drill: " Use a hard- tempered, spear-pointed steel drill in the engine, and while operating keep wet-with a solution of spirits of camphor and spirits of turpentine in equal parts. The cutting will be facili- tated by giving the hand-piece a slight rotary motion. If a contour filling is desired, grind off with the corundum wheel 464 MECHANICAL DENTISTRY. as much as is desired for ' contour/ after which make the retaining portion with the drill." Cavities, however, can be formed with greater facility in the use of the diamond point. With these general reflections concerning full dentures, we return now to a consideration of the mechanical or manipula- tive processes concerned in the construction of an entire denture attached to a swaged metallic plate by soldering. CHAPTER XIII. ENTIRE DENTURES ATTACHED TO A SWAGED METALLIC PLATE- BASE. Method of Constructing an Entire Upper Denture Mounted on a Swaged Metallic Plate-Base.—The general form and dimen- sions of the required base to be used as a support for a com- plete denture for the upper jaw may first be indicated by drawn lines upon the plaster model, and a sheet-lead pattern obtained from this to serve as a guide in securing the form of the plate to be swaged. The plate should be made sufficiently ample in its dimensions to cover all the hard palate, the alveolar ridge, and all portions of the external borders of the latter not directly encroached upon by the muscles and reflected portions of the mucous membrane of the lips and cheeks. Before swaging, the plate should be well annealed, and its central portion brought as nearly as possible to the form of the palatal face of the die with the mallet, forcing the heel of the plate down in advance of the portion covering the more anterior concavity of the arch, preventing thereby a doubling of the posterior edge of the plate upon itself. This central portion may also be forced more perfectly into adaptation with a partial counter before swaging in the ordinary manner, and this is advisable in all cases when the palatal arch is very deep; but as this is very liable to be drawn from the arch in the process of turning the borders of the plate over upon the ridge, a use- ful contrivance has been invented by Dr. Rurras, of New York, to prevent the displacement. Fig. 352 shows the form of this instrument. The die and plate are placed near the edge of the bench, and the upper part of the clamp adjusted over the central portion of the plate; the two pieces are then bound firmly to the bench by tightening the screw. A protective piece of buckskin, cloth, or paper, should be placed between the plate and the clamp to prevent the former from being bruised or indented. The margins of the plate are now turned 30 465 466 MECHANICAL DENTISTRY. Fig. 352. over upon the ridge, and if the external borders of the latter are undercut or stand even verticall v the edges of the former will tend to double upon themselves at such points, and hence it will be necessary, before swaging, to split the plate in front, and, in some cases, on each side, and wher- ever divided, a V-shaped piece may be cut out of sufficient width to allow the divided edges to over- lap slightly when approximated in the process of swaging. The proximate edges of the divided sections should be filed to a thin edge before swaging, so that when brought together and soldered there will be but little additional thickness of the plate at such points. The cut portions should not be soldered until after a partial or complete swaging. Having conformed the plate as nearly as practicable to the die with the mallet, or with plate forceps constructed for the purpose (Fig. 353), it should be placed between the die and counter, and the latter forced together with a heavy hammer until a tolerably accurate coaptation of the plate is obtained, the latter being frequently annealed during the process of stamping to render it more pliable. At first considerable yield- ing and consequent deformity of the counter-die will occur; hence, after partial swaging, another should be substituted and the process continued until the greatest possible accuracy of adaptation is secured. If the face of the die is marked by prominent and sharply defined rugae, or other irregularities, such points will, to some extent, be bruised or flattened ; it will therefore be expedient in such cases, and better, perhaps, in all, to finish the swaging with a new and unused die and counter, in which case two or three moderate, steady, and well-directed blows of the hammer will be sufficient. ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 467 If the plate is brought into uniform contact with all parts of the face of the die, this conformity is the only reliable test of its adaptation out of the mouth. In no case will the swaged plate fit the plaster model perfectly, inasmuch as the unavoid- able contraction of the die, however slight, will, especially in deep-arched mouths, cause the plate to bind on the posterior and external borders of the ridge, preventing it from touching the floor of the palate ; while the bruising, though inconsider- able, of the more prominent points upon the die, and a corre- sponding flattening of the plate at such points, will prevent uniform contact of the latter with the unchanged surface of the plaster model. After final swaging, the plate should be again annealed with a heat nearly or quite equal to that which will be ultimately Fig. 353. required in soldering ; after this any additional swaging should be avoided, unless the plate warps in the heat, and which may be determined by applying it to the die; if any change has occurred, it should be re-swaged and again annealed at a high heat, and the operation should be repeated, if necessary, until the plate retains its integrity of form after the last annealing. This process of final heating does not apply to silver if in the form of a swaged plate, as this metal invariably suffers some change of form when subjected to an annealing heat. Modifications in the Form of Plates for Entire Upper Den- tares.—Whenever a central air-chamber is employed, it may be constructed in either of the ways described when treating of partial atmospheric-pressure plates. The general form of a 468 MECHANICAL DENTISTRY. plate for an entire upper denture, with a central chamber, is exhibited in Fig. 354. Other modifications in the form of cavity-plates for full upper sets are in limited use, as where chambers are arranged one on each side of the sloping walls of the palate, or directly over that portion of the ridge previously occupied by the anterior molar and the bicuspids on each side. as seen in Fig. 355, called " Lateral Cavity Plates." Dr. M. Levett, o£ New York, has recently introduced another modifi- cation of cavity-plate, consisting of a number of small air- chambers arranged directly over the ridge and placed at short intervals throughout the entire border. It is claimed that plates constructed in either of the ways last mentioned cohere with equal firmness to the jaw, and are less liable to "rock " in the mouth, than when formed with a central chamber. What- Fig. 354. Fig. 355. ever their general utility may be, cases doubtless occur where they may be advantageously employed, as when any great in- equality exists in the hardness of the ridge and palate, and a plate constructed in the ordinary manner is dislodged by " riding " upon the hard palate when forces are applied to the ridge on either side. It has been recommended, after having constructed a base of the form represented in Fig. 354, to cut through the plate im- mediately in front of the central chamber, making an opening of a semilunar form. It is claimed that, by the more ready application of the tongue to this part, the air contained in the chamber, when the plate is applied to the mouth, may be more easily and thoroughly exhausted: There is great danger, how- ever, of the soft tissues being drawn into the opening, in which ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 461) ease it can scarcely fail to produce injury to the parts implica- ted ; the expedient, therefore, is seldom resorted to. There is still another form of cavity-plate known as Cleve- land's modification of air-chamber, and which is constructed in the following manner : A plate like that exhibited in Fig. 354 is first struck up and the chamber cut out.. A thin sheet of wax, or a layer of plaster, is then placed upon the lingual side of the plate, extending from two to three or four lines from the edges of the orifice in the main plate ; a thin, retreating edge is given to the wax or plaster of the outer borders, making it con- tinuous with the surface of the plate. The plate with the wax attached may now either be tacked to the model with softened wax along its outer borders, and shaped in such a way as to permit the model and plate to be withdrawn from the sand, and a mold of the parts taken in the ordinary way, and from Fig. 356. this a die and counter; or an impression in wax or plaster may be taken of the lingual face of the plate and wax, and afterward a model, die, and counter. With the latter, a second plate, covering nearly or quite all of the palatal concavity, is swaged, and when this is applied to the main plate over the cut chamber, and united by soldering, a space, equal to the thickness of the wax or plaster placed on the primary plate, will be found to exist between the two laminae. Fig. 356 exhibits a transverse section of the two plates, disclosing the space between them, and also the opening through the main plate into the cavitj'-. Before soldering on the duplicate plate, a half-round wire should be soldered around the opening in the palatal plate on its lingual side to protect the soft tissues of the mouth from injury when drawn in as the air is exhausted from the chamber; or, what is preferable, this form of cavity may be converted, 470 MECHANICAL DENTISTRY. practically, into what is known as " Gilbert's chamber " (which is the central swaged chamber before described), by filling in the space between the two plates with some impervious sub- stance, as Hill's filling, or an amalgam of gold, the excess of mercury being driven off by heat. In the construction of con- tinuous-gum work, the interspace may be filled in with gum body. The advantages of these double plates are, a greatly increased strength imparted to the base, a diminished liability of warping in the process of soldering, and a smoother surface presented to the tongue. In whatever wTay the plate is formed, a notch or fissure of sufficient depth to receive and permit an unobstructed play of the frsenum oi" the lip should be formed in the front part of the plate, while the borders of the latter nearly opposite the ante- rior molars on each side should be narrowed to prevent undue contact of its edges with the folds of the mucous membrane stretching obliquely across from the cheeks to the ridge. Care should also be taken to trim away from the heel of the plate any portions that might otherwise encroach upon the soft palate. It is only in the fewest number of cases that a rim can be swaged to form a groove or socket properly situated for the reception of the plate extremities of either single gum or block teeth, as it will usually be found impracticable to adjust the gum extremities to the socket thus formed without necessitating, in some degree, a departure from a just arrangement and an- tagonism of the teeth. Whenever it is thought best, therefore, to rim the plate, it will generally be necessary to adjust and solder a separate strip to the plate along its outer borders, and covering somewhat the gum portion of the artificial teeth rest- ing on the plate, after the arrangement of the latter on the base is completed. After the plate has been worked as nearly as possible into the required form, it should be applied to the mouth of the patient to ascertain the correctness of its adaptation to the parts before proceeding further with the operation. If the adaptation is found imperfect, the fault lies either in the impression, or in undue contraction of the die. In the former case, another im- ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 471 pression should be taken, and the plate re-swaged; in the latter, a less contractile metal or compound should be employed in the formation of the die. To determine the practical efficiency of the adaptation and adherence of an atmospheric-pressure plate, various tests may be applied. The coaptation of its borders to the external walls of the ridge may be ascertained by inspec- tion, and the patient's sense of contact or non-contact of its central portion with the floor of the palate may, in some degree, be relied on as evidence of the accuracy of its adjustment to parts not visible. The tenacity with which the plate adheres on the application of direct traction cannot always be relied upon, inasmuch as a well-fitting plate will sometimes be readily dislodged in this manner, while, on the contrary, one but illy adapted to the parts may require considerable force to separate it from the jaw when acted on in the same way. The most trustworthy test of actual or practical stability is firm pressure applied alternately over the ridge on each side and in front. If the plate maintains its position and remains fixed under repeated trials of pressure applied in the manner indicated, the adapta- tion may be safely relied on; if it slides upon the palate or is easily disengaged from the mouth, the instability of the plate may be referred in many cases, not to a want of coaptation, but to a want of uniformity in the condition of the parts on which the plate rests. These conditions have already been sufficiently considered. Method of Constructing an Entire Lower Denture Mounted on a Swaged Metallic Plate-Base.—Aside from the differences in the form of the plate, and the manipulations incident thereto, the process of constructing a plate for the under jaw does not differ essentially from that already described in connection with full upper dentures. If the lower plate is constructed from a single lamina of gold or other metal, it should be somewhat thicker than that used in upper cases, and should also be of finer quality, as the addi- tional thickness of the plate and the peculiar form of the in- ferior maxilla render a greater degree of pliancy necessary in swaging it to the form of the ridge. The general form of a base 472 MECHANICAL DENTISTRY. for an entire lower denture is exhibited in Fig. 357. The internal border of the plate should usually be doubled—either by turning the edge over in swaging, or by soldering on a nar- row strip of plate or half-round wire. A more perfect adaptation of the plate to the ridge may be obtained by the use of a double instead of a single plate, in which case a thin basement plate, not exceeding No. 30 of the gauge, should be swaged to the form of the ridge in the first instance, and then a duplicate plate, swaging the two together and uniting them to each other with solder. A plate of the specified thickness may be very readily and accurately con- formed to any irregularities in the ridge, and when the two are united the base will be heavier and stronger than a single Fig. 357. Fig. 358. lamina of the ordinary thickness. Instead, however, of dou- bling the entire plate, it will be sufficient, in most cases, to adapt the second plate only to the lingual surface of the first, extending it up from the lower edge to a point corresponding as nearly as possible with the posterior portions of the base of the teeth when the latter are adjusted to the plate (Fig. 358). A moderately thin plate may, in this manner, be used for the primary base, while the duplicate band will impart the requi- site strength to the plate, and, at the same time, obviate the necessity of wiring its inner edges. In adopting either of the last-named methods, the plates after they are united to each other should be again swaged to correct any change of form incident to the use of solder. ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 473 Antagonizing Model for an Entire Upper and Lower Denture.— Either of the following methods may be adopted in securing an antagonizing model for complete dentures:— 1. Attach to the ridge of each plate a roll or strip of adhesive wax corresponding in width to the length of the teeth which will be required for each plate respectively; place the plates with the wax attached in the mouth, and trim away from the proximate edges of the wax until the two sections close upon each other uniformly throughout the circle; then cut away from the labial surfaces of the rims of wax, above and below, until the proper fullness and required contour of the parts associated with the lips and mouth are secured. The approximation of the two jaws, when the finished substitutes are ultimately adjusted to the mouth, will depend altogether upon the aggregate width given to the two sections of wax at this stage of the operation, and it is, therefore, important that the " bite " or closure of the jaws secured at this time should be such as will most perfectly fulfill the requirements of the case in respect to the utility and comfort of the appliance, and the proper restoration of the required facial proportions. If there is any considerable change produced in the relation of the jaws habitual to them prior to the loss of the natural teeth, the characteristic expression of the individual will, in some degree, be changed or marred; an un- accustomed and restrained action will be imposed upon the muscles concerned in the movements of the lower jaw, which will render the use of the appliances at least temporarily, if not permanently, uncomfortable and fatiguing, or even painful; while the utility of the fixtures may be impaired or wholly destroyed by compelling a particular application of forces in mastication inconsistent with their stability in the mouth. No specific directions, of course, can be given that will apply to all cases, but it may be observed that, ordinarily, the two sections of wax should be cut away from their approximating surfaces until the jaws close sufficiently to permit the edges of the lips to rest easily and naturally upon each other when in a relaxed condition, or the upper rim may extend somewhat below the margin of the upper lip, while the lower section of the wax is cut awav on a level with the lower lip, or a little below it. 474 MECHANICAL DENTISTRY. Cases occur, however, where a less exposure of the upper por- tion of wax, even though quite narrow, will be required; as where the alveolar ridge is very deep, and the lip covering it either absolutely or relatively short, or where the latter is retracted, exposing, even when in a state of repose, a greater portion or all of the crowns of the teeth, and in extreme cases the margins of the gum. Between the latter extreme and an inordinate extension of the upper lip below the ridge all intermediate conditions occur, and the practitioner, aiming to produce an agreeable, harmonious, and truthful expression of all the parts, must rely wholly upon his judgment in reference to the neces- sary approximation of the jaws, the restoration of the natural fullness and contour of the mouth, and the relative length to be given to the upper and lower teeth. Patients when requested to close the mouth naturally, are very liable to project the under jaw; hence it is well to have them open and close the jaws frequently, observing at the same time if the separate portions of wax meet in precisely the same man- ner at each occlusion. If the bite varies at every approximation of the jaws, the patient should be directed to relax and abandon for the moment all control over the muscles of the lower jaw; the operator should then grasp the chin and press the jaw first directly backward and then upward until the opposing surfaces of the wax meet, in which position it should be steadily held by the patient until the two portions of wax are attached to each other in that particular relation. The latter may be done by drawing lines vertically across the rims of wax at various points, which will serve to indicate their relation to each other when out of the mouth; or a heated knife-blade may be passed between the two sections, the melted wax temporarily uniting them. A very convenient and secure method is to attach them together by means of two strips of metal bent in the form of a staple; these may be warmed in a spirit-flame, and pressed into the wax, one on each side—one end penetrating the upper rim of wax, the other the lower. Before removing the plates, the mesial line of the mouth should be indicated upon the wax by drawing a line vertically across the latter in front to serve as a guide in the arrangement of the central incisors. ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 475 2. Another method is to attach to either the upper or lower plate a single rim of wax somewhat wider than will be required for both the upper and lower teeth. The plates are then placed in the mouth, and the jaws brought together, imbedding the opposite plate in the wax. When this method is adopted, the proper closure of the jaws is best determined by a gauge or guide consisting of a strip of plate or other substance encased in the wax and interposed edgewise between the borders of the two plates in front in such manner that, when the latter are approximated, they will close upon the guide, the desired rela- tion of the jaws to each other having been previously ascer- tained by trial of the guide with the plates in the mouth before adjusting the wax. The exterior surface of the wax rim is then trimmed away, or additional portions added to it, until the proper fullness and contour are given to the lips; after which the medium line of the mouth should be traced upon the wax in front, as before described. The plates, attached to each other in either of the ways mentioned, having been removed from the mouth, a batter of plaster may be poured upon a piece of paper or other substance, forming a layer a fourth or a half an inch thick and two or three inches long, when the under surface of the lower plate may be imbedded in one end of the plaster, and the remaining portion of the latter projecting from the heel of the plate trimmed and formed for articulating with the second piece of the antagonizing model in the same manner as described when considering partial dentures. The entrance to the cavity between the two plates is now closed up with a sheet of softened wax or otherwise, and the whole surrounded by a piece of oil- cloth, wax, or other substance, and the second part of the model obtained by pouring plaster in upon the exposed surface of the upper plate and the plaster posteriorly to the depth of half an inch or more. When the plaster is sufficiently condensed, the line across the wax in front should be extended in a direct line across the borders of the plaster model above and below, as, in arranging the teeth, the wax will be cut away, and without this precaution the mesial point of the mouth may be lost. The form of an antagonizing model for an entire upper and 476 MECHANICAL DENTISTRY. Fig. 359. lower denture, with the plates and wax attached, the latter being cut away some- what preparatory to adjusting the teeth, is shown in Fig. 359. Antagonizing Model for an Entire Upper Denture with the Natural Teeth of the Lower Jaw Remaining.—In form- ing an antagonizing model to be used as a guide in arranging and articulating a full upper denture where all or a part of the natural organs of the inferior jaw are remaining, a rim of wax should first be adjusted to the borders of the plate, one or two lines wider than the required length of the artificial teeth. When placed in the mouth, the exterior surface of the wax draft should be cut away or added to until the proper fullness of the parts is restored. The patient should then close the lower teeth against the wax, imbedding them just sufficiently to indicate the cutting edges and grinding surfaces of the opposing teeth. If a fuller impression of the exterior faces of the lower teeth is required, it may be obtained by pressing in a small strip of softened wax against them and the lower edge of the rim of wax upon the plate; or the pro- jecting borders of the latter may be forced down upon the crowns with the fingers. The median line of the mouth is then indicated upon the wax, the plate removed, and its palatal surface imbedded in one end of a layer of plaster spread upon a strip of paper; the portion of plaster extending from the heel of the plate trimmed, grooved, varnished and oiled; the entire piece inclosed, and plaster poured in upon the exposed surfaces of the wax and plaster to the depth of one-fourth or one-half of an inch. The two sections of the model, with the plate and wax attached, the latter being cut away somewhat to receive the porcelain teeth, are exhibited in Fig. 360. Various articulators, or antagonizing frames, have been de- vised, and may be substituted for the plaster articulator just described. A very excellent adjustable contrivance of the kind, invented by Dr. Hayes, is exhibited in Fig. 361. With this appliance, all the motions of the Jaws can be represented, and the relative positions again brought back at pleasure at the ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 477 starting point. The screw hinge admits lateral motion. The set screw on the side plays into a slot, securing one central position, to which it can at all times, when desired, be brought back. The long screw in the foot produces back and forward motion, the main hinge up and down motion, and the large nut on the bottom renders all the parts taut and unyielding. Considerable space is here devoted to the consideration of an ingenious and novel device, introduced to the notice of the profession by Dr. W. G. A. Bonwill, of Philadelphia, Pa., and characterized by him as the " Anatomical Articulator." As to the character of this instrument, the author cannot speak personally. Dr. B., whose name is inseparably connected with the electric mallet, dental engine, original methods of Fig. 360. Fig. 361. attaching pivot crowns described elsewhere, and various other practical devices, says that it holds the same positive relation or position in his laboratory as do the electric mallet and engine in his operating room. In other words, it is indispensable to the perfect articulation of all artificial dentures from one to a full set,—that it is a sine qua non. He says :— " It is modelled on the same geometrical system as the human jaw. " I found by measurement that the average width of the lower jaw from centre to centre of each condyle was four (4) inches, and from the same centre of each condyloid process to the median line of the lower jaw, where the cutting edges of the lower incisors meet, was also four (4) inches, making of the 478 MECHANICAL DENTISTRY. human jaw an equilateral triangle. This holds good in all jaws, and the difference of a quarter of an inch in this radius of a circle of four inches would make but little practical dif- ference as to the results. " This beautiful law enables us to have the fullest benefit of mastication at the least expense of power and motion in the arc of the circle of four inches as a radius. " This being an absolute law, I have so made this articulator, and the cast of every case is set therein with the median line at the lower centrals just four (4) inches, by the dividers, from each condyloid process. If an unusually large jaw, then the cast is put a very little distance further out. " For all full sets, the articulation is so perfect, as made in this, in the laboratory, as to need but a trifling touch in fitting in the mouth. " I found that there is a further positive law in the mechan- ism of the human jaw that should be regarded in every sub- stitute made therefor, and, that is, just in proportion to the depth of overbite of the centrals, there is a curvature from the mesial surface of the first molars back, through the other molars, up the ramus. That this curvature upward and backward at the ramus is due solely to the depth of closure of the upper over the lower jaw. That where there is occlusion or closing of the cutting surfaces of the incisors directly upon each other, then a straight line, directly backward, is the consequence. If curved at the ramus, in such a case, no lateral or forward movement of the lower jaw could occur—only the up and down. "When there is an eighth of inch depth of bite, then, as you go back to the centre of motion—the condyloid pro- cesses—the cusps in the bicuspids and molars grow less deep, and the curvature at the ramus is an eighth of an inch out of line. " When there is an overbite of an eighth of an inch, then, in opening the lower jaw and carrying it forward to use the in- cisors for cutting, the back teeth of lower jaw are brought for- ward; and, as the second molar is higher out of line than the first molar, it comes in contact with the distal surface of the ENTIRE DENTURES ATTACHED TO SWAGED PLATE-BASE. 479 first superior molar, which begins just here to curve upward, and is the highest out of line in the superior jaw, and they meet at the same time that the incisors do. And the same law holds good when the lower jaw is turned to the right or left, the molars are brought in contact to equalize the force which would be brought upon the incisors only. Besides, the recog- nizing of this law enables the cusps or palatal and lingual sides of the molars of both jaws to be utilized in every position the lower jaw may take in mastication. Upon this plan I make all my artificial dentures, most of their articulating, surfaces being utilized at every position of the lower jaw. Any human jaw will show this system, which by this system can be made just as complete, and more so, in many cases, than the normal, or such as is found in advanced civilization. Fig. 362. " When a set is commenced in this articulator with the upper overbiting the lower an eighth of an inch, as you set each tooth backward toward the condyloid processes, they will assume the exact angle and depth of cusps, as well as the curvature at the ramus, as found in nature. If both jaws are in direct appo- sition at the incisors, then all of the teeth must of necessity be on a perfect plane, or but one would touch when in lateral position. u With this one base, which Fig. 363 shows, there is a sepa- rate bow to each part of base, one for upper and one for lower jaw, which can be removed as soon as the plaster in one case is allowed to harden on the rim. This can be marked and laid away for a year if necessary, and then articulated. A pair of 480 MECHANICAL DENTISTRY. bows can be used for as many separate cases, while only one base is required, which should be made absolutely and geomet- rically exact—approximately so. " There is no need for set screws to hold the bows, as they go up just so far and remain so Nor is there any set screw and prop to hold the jaws or casts apart. This is regulated on the bite in wax, which, before it is taken off the base plate, has the exact height marked by a pair of dividers on the plaster at the median line, measuring from the cutting edge of wax, and then when the first central or block is set, there is no longer any call for a prop to keep open the jaws of the articulator. When this height is taken with the dividers, it is marked on the top of each cast for future reference. It would interfere with the lateral Fig. 363. movement if a rigid prop were there. The dividers make each case exact without a scale for measurement. " Articulate the upper set first, and retain on the lower base the wax for length and fullness. When the upper are all on, then the lower incisors are gauged as to the height or length by the dividers while the wax is still on the base plate and taken from the height marked on the lower cast for reference. " Make the lateral movement as soon as the first tooth or block is in position where the case is an upper one with a good lower jaw of natural teeth. " When a full set, the upper are first ground on and shaped so as to meet the intended overbite, and when the lower set are ground on, the upper can be changed to suit the lower, so as to ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 481 allow the whole of every cusp to touch at nearly every lateral movement of jaw. " When the plaster case is to be set in the articulator, it must be done with the dividers set just four (4) inches, with one point at the median line as formed by the lower incisors, and the other carried over to each condyloid process as marked on the articulator. This makes the centre of jaw equidistant from the condyles. The study of this principle will make one fully realize the beautiful workings of Divinity, which is only gov- erned by positive law in every department of the universe. With this plan,. understand one will never again attempt to articulate a set of teeth on the unwritten law, as now univer- sally made and recognized by every dentist in the land. " Until this system is taught in the schools, and by private practitioners, no truly artistic and fully natural set of teeth can ever be made, for we have been without law in this department. To describe it is not enough. It must be seen and demonstrated, one tooth at a time, until the whole set is made. Only in this way can it be understood. " The Figs. 362 and 363 show clearly the simple construction. It is made of brass wire (one-eighth inch in diameter), and brass tubing to allow the size of wire to fit closely, and move freely therein when drawn out or pushed up. The spiral spring on either condyle allows of easy lateral motion to the lower part, and from exactly the same standpoint as in nature; that is, one of the lower condyles moves forward in the glenoid cavity while the other remains still. Every part of it is rigid except the movement at the condyles, and the joints or bows are only temporarily so. There is also an up and down motion made at the condyles by raising bow up or down. " No case, when once fixed in it, can become disarranged. If the bite in the wax is not correct, no articulator can make it so. You must go back again to the mouth, and retake it, which is easily done at first by asking the patient to swallow, when the jaws will automatically close and assume their normal position. If now correct, there is never any necessity for a screw to change it when once in this articulator. " There can be no excuse for failure or unartistic work when 31 482 MECHANICAL DENTISTRY'. this instrument is once understood, and the law controlling the human jaw. As we may forever have to resort to artificial dentures, we should demand of the colleges that such an instru- ment be used, and it alone, as furnishing the only hope now offered of an approach to high-toned, artistic, mechanical den- tistry. Until we can be taught to appreciate that law is the governor of the universe, and applicable in every branch of dentistry, we are false men, and will set 'false teeth/ and never realize our high destiny." Arranging and Antagonizing the Teeth; Rimming the Plate; Attaching Spiral Springs; Investing, Lining, Soldering and Fin- ishing.—In arranging or adjusting single gum teeth to the plate in those cases where the changes in the form of the alveolar ridge, consequent on absorption, are completed, the portions applied to the base should be ground away sufficiently to restore the required fullness of the parts and to give proper length and inclination to the teeth. The coaptation of the ground surfaces to the base should be accurate enough to ex- clude perfectly particles of food, and to furnish such a basis to each tooth as will provide most effectually against fracture when acted upon by the forces applied to them in the mouth. The gum extremities of the teeth should also be accurately united to each other laterally by grinding carefully from their proximate edges until the joints or seams will be rendered in- capable of ready detection in the mouth, care being taken that this coaptation of the adjoining surfaces is uniform, for if con- fined to the outer edge alone, portions of the gum enamel may be broken away in the process of soldering. In the construction of substitutes designed to fulfill only a temporary purpose, and where the alveolar processes remain in a great measure unabsorbed, and plain teeth (those represent- ing but the crowns of the natural organs) are used, but little skill will ordinarily be required in adjusting and fitting them to the base. If the ridge in front is prominent and but inade- quately concealed by the lip, as where the teeth have been but recently extracted, all those portions of the border of the plate in front, anterior to the first or second bicuspid on each side, may be cut away on a line a little within the required circle of ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 483 the anterior teeth, and scolloped (Fig. 364), permitting the anterior cervical portions of the artificial incisors and canines, and, in some cases, the anterior bicuspids, to overlap the edge of the plate and rest directly upon the gum in front. This abridgment of the plate will not ordinarily materially affect the adhesion or stability of the substitute. There are cases of a mixed character that render it more difficult to effect a harmonious and symmetrical arrangement of the teeth, as where a limited number of the natural teeth at intervals have been long absent, and the excavations in the ridge consequent on absorption alternate with other points upon the ridge in a comparatively unchanged condition. To give uniformity to the denture by restoring perfectly the required circle of the arch in such cases will necessitate the employment of plain and single gum teeth conjointly. Whenever necessary, those portions of the base occupied by the plate teeth may be cut away in such a manner as to permit the latter to be adjusted directly to the unabsorbed gum as before described. In the process of grinding the teeth to the base, above and below, the operator should commence by first arranging the superior central incisors, and then the lower, and so passing back from tooth to tooth, grind and adjust an upper and lower tooth alternately, keeping the upper ones in advance of those of the lower jaw. The central incisors above should be placed parallel with each other, but the cutting edges of the laterals, and the points of the canines, should incline slightly toward the median line of the mouth. In arranging the teeth of the upper jaw, the anterior six may be made to describe, with more or less exactness, the segment of a circle, but a somewhat abrupt angle may be given to the arch on each side by placing the first bicuspid within the circle in such a way that, when standing directly in front of the patient and looking into the mouth, only a narrow line of the exterior face of the crowns of these teeth will be seen, while the remaining teeth posterior to them should be arranged nearly on a straight line, diverging as they pass backward. When arranged in the manner described, the peripheral outline of the arch will exhibit somewhat the form presented in the diagram (Fig. 365). 484 MECHANICAL DENTISTRY'. In regard to the practical efficiency of an upper denture re- tained in the mouth by atmospheric pressure or adhesion, it is important that the teeth engaged in the comminution of food, as the bicuspids and molars, should'occupy a position directly over the central line of the ridge, and should either be arranged vertically or with a slight inclination toward the centre of the mouth. The liability to displacement of the substitute in mas- tication will thus be greatly diminished, whereas, if placed out- side of the line indicated, and especially with a diverging incli- nation, the stability of the appliance will be endangered, and the functions of mastication impeded, notwithstanding other conditions necessary to complete success have been fully secured. In arranging the upper and posterior teeth as de- scribed, it will sometimes be necessary to give to the opposing Fig. 364. Fig. 365. under teeth a decided inward inclination in order to effect a satisfactory antagonism of the teeth; and cases occur where a practical articulation cannot be secured without departing in some degree from the arrangement of the upper teeth spoken of,—as where a great disparity exists between the posterior transverse diameters of the two jaws, a medium-sized, or even small, arch above being associated with an expanded ridge below. In articulating the upper and lower teeth, the normal occlu- sion of the natural organs should be imitated as nearly as the other essential requirements of the case will admit of. Hence the upper front teeth, describing the segment of a larger circle than the corresponding teeth of the lower jaw, will project ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 485 beyond and overlap slightly the cutting edges of the latter; and having a greater width of crown, they will extend laterally beyond the opposing teeth, covering one-third of the crowns of those next adjoining, so that when the canines of the upper jaw are reached, they will close between the lower canines and first bicuspids; and, passing back, the anterior superior bicus- pids between the first and second bicuspids below; the posterior bicuspids above between the second inferior bicuspids and an- terior molars; the first superior molars between the first and second molars below; while the anterior half of the posterior molars above will close upon the posterior half of the inferior second molars, the remaining posterior half of the second molars above extending posteriorly beyond those of the lower jaw. The outer cusps of the superior bicuspids and molars Fig. 366. will overlap those of the inferior teeth; while the inner cusps of the teeth of the superior jaw will pass into the depressions in the lower teeth formed by the internal and external cusps, and the external cusps of the inferior teeth will, in like man- ner, be received into the corresponding excavations of the upper teeth. The relative position and antagonism of the teeth, as they appear in a regularly arranged denture for both jaws, are shown in Fig. 366. An abnormal relation of the jaws, as where undue projection, absolutely or relatively, of either maxilla exists, or where the lower jaw closes on one side or other of the upper, will frequently compel a departure from the ordinary arrangement of the artificial organs, the extent" of which must be determined by the necessities of each individual case. 486 MECHANICAL DENTISTRY. In selecting teeth for a full upper denture in those cases where natural teeth are remaining below, or vice versd, the color, size, and form of the latter will serve as a guide in the choice of teeth appropriate for the opposite jaw. In fitting and arranging the teeth upon the base, and in antagonizing them with the opposing natural teeth, the same general principles apply as those already adverted to in connection with full upper and lower dentures. Having adjusted the teeth to the base, they should be placed in the mouth, before uniting them permanently to the plate, to detect and remedy any error of arrangement either in respect to prominence, position, inclination, length or antagonism. Forming a Rim to the Plate.—If the case is one where single gum or block teeth are employed, and it is intended to form a socket or groove upon the borders of the plate for the reception of the plate extremities of the teeth, the rim forming the groove should be fitted and soldered to the base before investing the piece in plaster. If the alveolar ridge above is shallow, and but imperfectly concealed by the lip, a rim to the plate will be inad- missible, as, when the mouth is opened and the lip retracted, as in laughing, the metallic band will be exposed to view. A rim may be fitted and attached to the base in either of the following ways:— 1. A strip of plate from one to two lines in width is adjusted to the plate, with one edge resting on the uncovered border of the plate close to the gum extremities of the teeth, and the other overlapping and embracing the latter. The rim may consist of one entire strip extending from heel to heel of the plate, and passing round the posterior molars to unite with the stays; but it may be more conveniently adjusted by employing two pieces, extending from each heel of the plate, and uniting in front. 2. A half-round wire with the edge beveled where it joins the ends of the teeth, forming a narrow groove, may, in like man- ner, be fitted to the plate, furnishing a shallow bed for the gum extremities of the teeth. A narrow strip of plate, about the thickness of heavy clasp material, may be substituted for the half-round wire. In either case, the better plan is first to trace ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 487 the outlines of the gum portions of the teeth upon the plate with a sharp instrument; remove the wax and teeth from the plate; draw another line a little within the first all round, and solder the rim to the line last drawn; remove the teeth from the wax, and readjust the latter in its proper place upon the plate; then fit each tooth separately to the rim by grinding away sufficiently from the end of the tooth to effect an accurate adjustment of it to the socket. The ends of the teeth may be ground away to the rim until the platinum pins freely re-enter the rivet-holes in the wax, thus restoring them to their proper position in relation to the base. 3. Another method of forming a rim consists in swaging a strip of plate accurately to the form of the parts to which it is applied. An impression in wax or plaster is first taken of the gum surfaces of the teeth and exposed border of the plate; but as it will be impossible to detach either wax or plaster in per- Fig. 367. feet condition, when encircling the entire arch, or to swage perfectly with a die so unfavorably formed for stamping, sepa- rate impressions of the two lateral halves of the piece should be taken—from these plaster models ; and from the latter, dies and counters;—with. these, two strips of plate of sufficient width are swaged, each extending from the heel of the plate to a little beyond the median line in front, overlapping slightly at the latter point. The portions of the swaged strips embrac- ing the plate ends of the teeth are then trimmed to the proper width, and scalloped, if desired, in correspondence with the festoons of the artificial gums. An upper denture rimmed in the manner last described is exhibited in Fig. 367. In what- ever way the rim is formed, when it has been fitted to the plate and teeth, it may be held temporarily in place with clamps adjusted at two or three points around the plate and then trans- 488 MECHANICAL DENTISTRY. ferred to a piece of charcoal, and secured by first tacking it at two or three points with solder. The groove may then be filled with whiting, mixed with water or alcohol, to prevent the solder from flowing in and filling it up; after which small pieces of solder are placed along the line of union next the edge of the plate, and the rim permanently united throughout with the blowpipe; after which the wax and teeth are re-applied to the plate. Constructing and Attaching Spiral Springs.—The success which has been attained in the use of atmospheric pressure and adhe- sive plates has almost entirely superseded the necessity of em- ploying spiral springs as a means of support; nor should the latter be resorted to except under circumstances that preclude the use of the former. When applied, they should be attached to the base on each side between the posterior bicuspid and first Fig. 368. molar below, and opposite the posterior bicuspid above. To the border of the plate near the base of the teeth a narrow strip of plate is soldered, extending up and lying closely against the side of the latter—to the end of which near the grinding sur- faces of the teeth is adjusted a small circular cap of gold con- nected with the standard by a small wire on which the looped extremity of the spring plays. To each end of the spring is attached a gold wire, doubled upon itself in such a way as to form a loop, the closed ends being soldered together and filed to enter the hollow in the wire, A, Fig. 368. B, Fig. 368, copied from Professor Harris's work on dental surgery, represents an- other method of attaching springs, but the former is more readily constructed and will answer every practical purpose. Fig. 369 exhibits the application of springs to an upper and lower denture. ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 489 Investing, Lining, Soldering and Finishing the Plate.—The plate, with the wax and teeth in place, is next encased in a mixture of plaster preparatory to lining the teeth and uniting them with solder to the base. For this purpose, plaster and sand may be employed, using as little of the former as will serve to hold the investment together during the subsequent manipulations. Asbestos may be added, and is a useful ingredient. Burnt plas- ter, or that which has been previously used for investing, may be substituted for the sand and asbestos, adding a sufficient quantity of unused plaster to effect consolidation. Either of the combinations mentioned will suffer but little change in the fire, if properly managed. It is customary to incase the piece in the plaster mixture to the depth of from one-half to three- fourths of an inch, leaving only the lingual surfaces of the Fig. 369. plate and teeth uncovered. However comparatively free from change of form the best combinations of plaster may be, yet some slight contraction of the body of the investient doubtless ensues on the application of heat, and it is probable that so large and resistant a mass must tend, in some degree, to pro- duce deformity of the plate in soldering; for, as the investient contracts and the plate at the same time expands when heated, a change in the form of the latter must occur whenever the force exerted by the shrinking plaster exceeds the expansive force of the metal; and when the peculiar form of the upper plate is considered we can readily conceive how a slight con- traction of the plaster of the thickness mentioned may " warp " or "spring" the plate when its uniform linear expansion and contraction is so effectively opposed. The change in the form 490 MECHANICAL DENTISTRY'. of the base from this cause will, according to the author's obser- vations, be found, in an upper plate, to exist on each side of the sloping walls of the palate, embracing the posterior half or two- thirds of the plate at these two points—the change manifesting itself in an inward displacement of the lateral walls of the plate midway between the summit of the palatal arch and the most depending portion of the ridge. We would suggest in explana- tion of this result that, as the plaster contracts with sufficient force to carry the plate with it, the sides of the latter are ap- proximated, while the palatal portion is at the same time lifted up. Now it seems plain that inasmuch as the portions of plate overlapping the ridge are encased in and embraced by the plaster, and as the palatal portion is arched in form with its convexity presenting to the plaster, and therefore self-sustaining in respect to its own peculiar form, the special configuration of these parts cannot suffer any appreciable change; but as they are forced toward the common centre of the mass, their relation to each other is also changed, and this changed relation must necessarily eventuate in a deformity of those parts of the plate which offer the least resistance to the contractile force of the plaster. In obedience to this necessity, the sides of the plate along the sloping walls of the palate, which from their form are neither resistant nor self-sustaining under pressure, and whose inward displacement is unopposed by any counter-force, are projected in toward the centre of the palatal excavation in proportion as the borders and central portions are approximated or converged in the direction of the centre of the piece. The practical effect of this approximation of the lateral and posterior borders, and internal displacement of the plate, is to make the latter " bind " upon the outer and posterior borders of the alveolar ridge, and to throw the central portion of the plate from the roof of the mouth. To obviate, as far as practicable, any change in the form of the plate which may result from the contraction of the plaster investient, various expedients have been suggested, but the following will sufficiently counteract the influence of the plaster by permitting an unobstructed expansion and contrac- tion of the metallic base. Take a band of tolerably thick copper plate as wide as the plate and teeth are deep; bend it to ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 491 the form of the plate, but large enough to leave a space of nearly half an inch between it and the teeth, the ends being united to each other back of the plate by riveting or otherwise. Holes are then made in the band at numerous points through- out its extent, through which wire is introduced and interlaced on the inside in such a way as to form loops, the latter extend- ing in to within a short distance of the teeth. The plaster is then filled into the space between the band and teeth even with the cutting and grinding surfaces of the latter; the palatal sur- face of the plate is also covered with plaster and may be con- nected with the outer portion by a very thin layer at the edge of the plate, or the two may be entirely disconnected. The expansion of copper being very nearly that of gold, the body of the plaster, when heat is applied, will be carried in advance of the borders of the plate as the latter expands, while the thin portion of plaster at the edges of the plate will allow the central portion of the latter to expand with but little or no interruption. On cooling, the entire mass will contract together and assume its original form, unless warping is induced by other agencies acting independently of the enveloping plaster, as excess or unequal distribution of solder, irregular heating, etc. It is not, ordinarily, necessary to provide by any special ex- pedient against warping of the lower plate, as any slight change of form consequent on contraction will not materially affect its adaptation to the lower jaw,— its only effect being to impart to the substitute a slight lateral play upon the ridge. The plaster on the inside of the lower piece may be cut away to the edge of the plate, while that external to the teeth should not be added in greater quantities than is barely sufficient to hold the latter in place whilst lining and soldering them to the base. The plate being properly invested, all portions of the wax attached to the inner surface of the teeth and plate should be thoroughly removed with suitable instruments; after which stays are to be adjusted to the teeth. In reference to the method of forming and adjusting stays, little need be added to what has already been said when treating of partial dentures. One method, not there specified, consists in first fitting to each tooth separately, in the usual manner, a thin stay formed of 492 MECHANICAL DENTISTRY. platinum, which is temporarily fastened to the tooth by split- ting and spreading apart the ends of the rivets with a small chisel-shaped instrument. The teeth. are then removed from the investient and partially imbedded side by side in plaster, the platinum strips remaining uncovered. The plaster and teeth may then be raised to a full red heat with a blowpipe or by placing them in the furnace. Small pieces of gold plate, of equal fineness with the base, are then placed upon the surfaces of the platinum stays and thoroughly fused with the blowpipe until they flow perfectly in around the rivets, and uniformly over the surface of the linings. If sufficient heat is applied, the solder will insinuate itself between the stay and tooth, and thus render the coaptation of the two perfect. Small pieces of gold plate should be added until sufficient thickness is imparted to the linings. The backings are then trimmed smoothly and burnished, when they may be placed back in the investient in their appropriate places. The linings which support the teeth may be united to each other laterally in sections or continu- ously. When the teeth are joined to each other throughout, a very small quantity of solder will be sufficient to support the teeth, provided it is well diffused along the joints uniting them perfectly at all points. The process of preparatory heating, soldering, pickling, and finishing the plate, is the same in all respects as that described when treating of partial pieces, and need not, therefore, be re- capitulated. In the final adjustment of the finished piece to the mouth, and after any additional grinding of the masticating surfaces of the teeth necessary to perfect the antagonism has been per- formed, such instructions should be given to the patient in regard to the care and management of the appliances as will best promote their immediate and successful use. The wearer should be impressed with the absolute necessity of early and prompt attention to any injuries inflicted upon the soft tissues of the mouth by the substitutes, as 'much future trouble and annoyance, if not permanent mutilation of the parts, may result from neglect, but which may be readily averted, in most in- stances, by a timely removal of the sources of injury. To ENTIRE DENTURES ATTACHED TO A SWAGED PLATE-BASE. 493 obviate, in some measure, the tendency to displacement of the base, which usually accompanies the first use of artificial teeth, and especially the upper denture, the patient may be directed, when dividing food with the front teeth, to press the substance backward and upward against the cutting edges of the superior incisors at the same time that the opposing teeth are closed upon each other, thus dividing completely the substance seized. In reference to the mastication of food, it has been suggested to instruct the patient to distribute, by the action of the tongue, the portions of food as equally as possible on each side of the mouth, in this manner distributing the forces applied, and thereby lessening the chances of lateral displacement of the substitute. CHAPTER XIV. PORCELAIN TEETH—CARVED BLOCK-TEETH. PORCELAIN TEETH. The perfection and completeness of results attained at this day in the production of porcelain teeth, approximating so nearly the natural organs in all their more obvious, physical, and distinctive characteristics as to be almost, if not quite, un- distinguishable from the latter when applied in obedience to the aesthetic requirements of individual cases, is one of the marvels of ceramic art. Nowhere, perhaps, have the conceptions of genius been embodied in porcelain with more truthfulness or greater fidelity to nature than in the exquisite and wonderful imitations of the dental manufacturing laboratory. So amply and satisfactorily has the intelligent, progressive, and well-directed enterprise of manufacturers provided for all the ordinary needs of prosthetic practice in the almost endless variety in size, color, configuration, relation, and adaptability of single and sectional teeth, that the work of hand-carving is now rarely demanded of the general practitioner except in ex- treme cases resulting either from accident or disease. Thus, as aptly remarked by the late Professor Austen, " The depot not only renders service by the superior excellence of the surgical instruments and prosthetic materials which it supplies, but it directly benefits the science and art of dentistry by releasing the practitioner from manufacturing toil, and giving time for the acquirement of increased knowledge and skill. Thus, if the time heretofore given to block-making were devoted to the study of dental aesthetics, patients would have the benefit of an artistic selection from a far larger variety of porcelain dentures than could otherwise be possibly made." As affording some curious as well as practical information in regard to the composition and manufacture of porcelain teeth, the following descriptions will be found of interest:— 494 PORCELAIN TEETH. 495 Components of Dental Porcelain.—Manufactured single and sectional mineral teeth, carved block-teeth, continuous-gum material, etc., are composed of two distinct portions,—the body or base, and enamel. The chief mineral substances which compose the body are silex, felspar, and kaolin. The enamel, both crown and gum, consists principally of felspar. The various tints or shades of color are imparted to the porcelain by certain metals in a state of minute division or their oxides. The more general properties of the mineral in- gredients will be first described. Silex,—Silex, silica, or silicic acid, is a white powder, in- odorous, and insipid. It forms the chief part of many familiar mineral formations, as quartz, rock-crystal, flint, agate, calcedon, and most sands and sandstones, in some of which it occurs nearly pure. Silica, in its pure state, is insoluble in water or acids, and is infusible in the highest heat of the furnace; it melts, however, in the flame of the oxyhydrogen blowpipe, passing into a transparent colorless glass. Its specific gravity is 2.66; and it is composed of silicon, 48.04, and oxygen, 51.96. Only the purest varieties of silex are employed in the manu- facture of porcelain teeth. It is prepared for use by subjecting it to a white heat and then plunging it into cold water, after which it is ground to a very fine powder in a mortar. Felspar.—This mineral substance occurs crystallized in oblique rhomboidal prisms, and is a constant ingredient of granite, trachyte, porphyry, and many of the volcanic rocks. The felspathic mineral formations present either a pearly or vitreous lustre, and vary in color, being red, green, gray, yellow, brown, flesh-colored, pure white, milky, transparent, or translucent. Felspar yields no water when calcined; melts at the blowpipe into a white enamel, and is unaffected by acids. It is composed, according to Rose, of silica, 66.75; alumina, 17.50; potash, 12; lime, 125; oxide of iron, 0.75. It is found in various localities throughout the United States, the purest and whitest kinds being employed in the manufacture of mineral teeth. It is prepared for use in the same manner as silex. Felspar, from its ready fusibility, serves to agglutinate the particles of the more refractory ingredients, silex and kaolin; 496 MECHANICAL DENTISTRY'. and when diffused throughout the mass imparts to the porce- lain a semi-translucent appearance. Kaolin.—Kaolin, or decomposed felspar, is a fine white variety of clay, and is composed chiefly of silica and alumina, the latter being the characteristic ingredient of common clay. It is found in various localities throughout the Eastern States, and in parts of Asia and Europe. Kaolin is refractory or fire- proof, but is rendered more or less fusible by the contamina- tions of iron and lime with which it is usually combined. The opaque and lifeless appearance characteristic of the earlier manufacture of mineral teeth was due to the introduction of a relatively large proportion of this clay into the body of the porcelain. The peculiar translucent and lifelike expression which distinguishes the beautiful imitations of the present day, is due, in great part, to the comparatively small proportion of kaolin clay, and an increased amount of the more fusible and vitreous component, felspar. Kaolin is prepared for use by washing it in clean water; the coarser particles having settled to the bottom, the water hold- ing the finer ones in solution is poured off, and when the suspended clay is deposited at the bottom of the vessel, the water is again poured off, and the remaining kaolin dried in the sun. Coloring Materials.—The following metals and oxides are employed in coloring mineral teeth; titanium, platina sponge and oxide of gold being those chiefly used in producing the more positive tints, and by combining which, in varying pro- portions, any desired shade of color may be obtained. METALS AND OXIDES. COLORS PRODUCED. Gold in a state of minute division,.....Rose red. Oxide of gold,..............Bright rose red. Platina sponge and filings,.........Grayish-blue. Oxide of titanium,............Bright yellow. Purple of Cassius,............Eose purple. Oxide of uranium,............Greenish-yellow. Oxide of manganese,...........Purple. Oxide of cobalt,.............Bright blue. Oxide of silver,.............Lemon yellow. Oxide of zinc,..............Lemon yellow. PORCELAIN TEETH. 497 As the preparation of most of the above colors requires great care, and a somewhat intimate knowledge of chemistry, and as the most delicate manipulations are necessary to secure accu- rate and satisfactory results, it is better for the mechanical operator to procure the coloring ingredients already prepared from some competent chemist, rather than attempt their pro- duction himself. For a particular description of the various modes of preparing them, "the reader is referred to Piggot's Dental Chemistry and Metallurgy, and other works treating fully of the subject. Manufacture of Porcelain Teeth.—The subjoined account of the processes concerned in the manufacture of porcelain teeth is descriptive of those at present employed in the manufactory of the late S. S. White, and which, in the main, are doubtless the same as those of other leading establishments. The felspar is first calcined by throwing it in large masses into a furnace, and subjecting it to a red heat and then plung- ing it into water, which renders it brittle and easily broken by the hammer into small pieces, so that all foreign matters, such as mica or iron, with which it may be mixed, can be separated. It is then crushed between flint stones, and when fine enough is afterward ground under water in a mill in which heavy blocks of French bur-stone revolve upon a nether millstone of the same material, until sufficiently pulverized, when it is floated off and allowed to settle. After this the water is drawn off or evaporated, and the deposit of spar dried and sifted. The silex is subjected to the same treatment. The kaolin, already of the desired consistence as found in nature, is prepared for use by first washing out impurities, and then drying. The mineral ingredients are ground somewhat coarsely, but the coloring materials are reduced to an impalpable powder by means of a mortar and pestle machine of great power. When properly prepared, the several materials are combined in suitable proportions to form the body and enamels, and are then mixed with water, and worked into masses of the required consistence for molding. The degree of plasticity of the body and enamel pastes differ with the methods of manufacture. 32 498 MECHANICAL DENTISTRY'. Formerly, the teeth, when molded, were first exposed to a heat just sufficient to produce partial baking of the body, and this was called cruising or biscuiting, after which a thin paste of enamel material was applied with a camel's-hair brush, and the whole subjected to a second heat for complete and final fusion. This preliminary process of biscuiting is essential in carved block and continuous-gum work, but in the S. S. White factory, and probably others, this partial baking is dispensed with, and the body and enamel pastes of the uniform consistency of putty are introduced into the molds, in the first instance, properly distributed, and final fusion effected by a single exposure to heat. The molds are made of brass and are in two sections, one- half of the tooth being represented on either side. The exact form of the tooth or teeth is carved out with great care and precision, and must be anatomically correct and mechanically perfect, while the matrix is made about one-fifth larger than the required size to compensate for shrinkage of the materials in baking. Holes are drilled in each half of the mold to receive the platinum pins, and the exact closure of the two pieces of the mold secured by guiding pins. The molds having been previously greased, and the platinum pins, which vary in length and thickness to meet special re- quirements, placed with small tweezers in the holes provided for them, the crown and gum enamels are first carefully laid in with small steel spatulas in the required quantity and position. The body is then added, in quantity exceeding somewhat the capa- city of the mold, when the sections of the mold are closed upon each other and subjected to a pressure sufficient to insure compactness of the inclosed mass. When thoroughly dried by a slow heat, to which the molds are exposed, the teeth are readily disengaged when the matrix is separated, and will be found at this stage extremely friable and tender, requiring great care in handling them. They are then sent from the molding to the trimmer's room, where, after critical inspection, all defective ones are either repaired or condemned, all excess of material filed smoothly . away, and the arch of the gum over each tooth made true and CARVED BLOCK-TEETH. 499 smooth with fine pointed instruments. They are then placed on beds of coarse quartz sand, on fire-clay trays or slides ready for the furnace. Referring to this stage in the process of manufacture, an in- telligent observer writes:— " Beyond this, no tool can follow them. Imperfections here- tofore could be repaired, but in the future, beyond the fire, the tooth is either perfect or a failure irremediable. The furnace is an institution entitled to respect for its intensity. In its centre is a muffle of fire-clay, entirely surrounded by the glow- ing fuel, a charge of half a ton's weight of coal, itself carefully bricked up before firing, that no impurities of dust or vapor shall reach the teeth. Take out the small half-oval door of the muffle and you will see an inner glow the eye shrinks from registering, an incandescence that startles you by its fervor. In from fifteen to thirty minutes, teeth and fire-clay slide, glowing like the oven, are taken out done and finished. The dull enamel has become as glass. The lustreless oxides have yielded their color, and the tooth that went in friable and brittle has come out adamant. But there is an intermediate skill, the acquisition of which is one of the marvels of the mechanic arts. A little too long in that heat and the teeth are ruined, and the evils of ' underdone' are equally to be guarded against as in the housekeeper's baking. It is a trained judgment, a skill of eye and handling that enables the burner to lend success to the work of those who have gone before him, and at the precise point where a shade of failure is utter ruin. " The teeth are now done and ready for the curious, charac- teristic red wax cards, on which they go to the trade." CARVED BLOCK-TEETH. The fabrication of porcelain block-teeth constitutes a some- what distinctive branch of practical dentistry, and from the delicate nature of the manipulations, and long experience neces- sary to attain to any considerable degree of excellence in the various processes connected with their manufacture, their con- struction is seldom attempted by those engaged in general practice. Cases occasionally present themselves, however, 500 MECHANICAL DENTISTRY. which, by reason of unusual or unequal absorption, or exten- sive and irregular loss of tissue as the result of accident or disease, demand, for their successful treatment, specific forms of dental substitutes not obtainable from any collection of ready-made teeth, single or in sections, however large or varied. To meet properly such possible exigencies of practice, either the services of an experienced block-workman must be ob- tained, or the demands of the case must be* supplied by such skill as the general practitioner can bring to the work. To the latter, the following descriptions of the process may prove helpful. A description of the general properties of the several in- gredients, earthy and metallic, used in the formation of block- teeth, has already been given in the preceding part of the present chapter. The method of compounding and preparing the materials will next be given, with various approved recipes for body and enamel. Composition and Preparation of the Body.—The porcelain paste for the body of block-teeth may be compounded from either of the following formulas. There are a great variety of recipes, differing more or less in the proportion of the com- ponent ingredients, but the following will be found to answer every practical purpose, and are such as are generally employed at this time by experienced block-workmen :— ^'o. I. NO. III. Delaware spar, 12 oz. Spar, . . . . 12 oz. Silex, .... 2 oz. 8 dwts. Silex, .... 2 oz. 8 dwts. Kaolin, ... 1\ dwts. Kaolin, ... 12 dwts. Titanium, . . 18 to 36 grs. Titanium, . . 24 grs. *0- H. NO. IV. Delaware spar, 16 oz. Spar, . . . . 8 oz. Silex. .... 3J oz. Silex, . . . . 1J oz. Kaolin, ... J oz. Kaolin, ... 4 dwts. Titanium, . . 20 to 60 grs. Titanium, . . 22 grs. xo. v. Spar, .... 2 oz. Silex, .... 8 dwts. Kaolin, . . . 2 dwts. Titanium, 4 grs. CARVED BLOCK-TEETH. 501 The titanium is first ground in a mortar until reduced to an impalpable powder; the silex is then added and ground from one to three hours, or until there is no perceptible grit; after which the kaolin is added and thoroughly ground; and lastly the spar, adding small portions at a time, and grinding the whole until perfect comminution and intermixture of the several ingredients are effected, say from half an hour to an hour. The ingredients may be ground dry or in water,—in the latter case a sufficient quantity of clean rain-water should be added from time to time, to form a mixture of about the consistence of thick cream. After sufficient comminution is effected, the surplus water may be abstracted by pouring the mixture upon a clean, dry slab of plaster-of-Paris. When it acquires about the consistence of thick dough, it should be beaten with a wooden mallet, or thrown repeatedly and forcibly upon a marble slab, and, if prepared in quantities for future use, it should be preserved in its plastic state by confining it in a closely-stopped earthen jar. When ground dry, the materials are prepared for immediate use by adding to the powder clean rain-water in sufficient quantity to form a thick paste ; it is then well beaten on a porcelain or marble slab, and pressed, just before using, between folds of cloth, to expel per- fectly all particles of air that may be confined in the body of the paste. Composition and Preparation of Crown Enamels.—The enamel, which forms the external covering to the crowns of porcelain teeth, is composed wholly of felspar, with such coloring matters as serve to communicate to it the various tints or shades of complexion characteristic of the natural organs. The more positive tints, grayish-blue and yellow, are produced by tita- nium, platinum sponge, and oxide of gold; intermediate colors being produced by varying the special combinations of these ingredients. The following recipes will furnish various tinted enamels, the varieties of grayish-blue being applied to the points or coronal extremities of the teeth—the yellow to the necks: the two colors being so blended when applied as to run imperceptibly into each other. 502 MECHANICAL DENTISTRY. GRAYISH-BLUE ENAMEL. NO. I. SO. III. . 2 oz. . . 2 oz. • • igr. Platina sponge, • • fgr. NO. II. • • Jgr- Oxide of gold, NO. ■ • i gr- IV. . . 2 oz. . . 2 oz. ■ • igr. • • igr. Flux,f . . 24 gr. Platina sponge, • . igr. YELLOW ENAMEL. NO. I. NO. in. . . 2 oz. . . 2 oz. . . 10 grs. . . 16 grs. Platina sponge, . . • • igr. Platian sponge, . ■ • igr. NO. II. . . igr- Oxide of gold, . NO. • • 2gf> IV. . . 2 oz. , . 2 oz. Flux, ..... , . 20 grs. Platina sponge, . . . • • i gr- . 10 grs. Oxide of gold, . . . • • igr. In compounding enamels from the foregoing recipes, the coloring ingredients should first be ground to a very fine powder, with five or six dwts. of the spar; the remaining por- tions of the latter should then be added, a little at a time, and ground for half an hour or more. The shades of color may be varied almost indefinitely by changing the proportions of the coloring matter. GRAYISH-BLUE ENAMEL. NO. I. NO. II. Spar,.........1 oz. Spar,.........1 oz. Blue frit, X.......5 grs. Yellow frit, \......4 grs. Gold mixture, ||.....20 grs. * The Boston spar is preferred on account of its greater fusibility. f Flux is composed of silex, 4 oz.; borax, 1 oz.; sal tartar, 1 oz.; these are ground to an impalpable powder and packed in the bottom of a clean, light- colored crucible. A piece of fire-clay slab is then fitted into the top of the crucible and luted with kaolin clay. It is then exposed to the heat of a furnace until completely fused, when it is removed, and when cold the crucible is broken, all foreign particles or discolored portions thoroughly removed, and the remain- der well pulverized. % Blue frit is composed of spar, i oz.; platina sponge, 4 dwts.; powder finely, make up into a ball with water, and fuse very slightly upon a slide in a furnace. It is then plunged into water while hot, and when dry, finely pulverized. \ Yellow frit is made by mixing intimately i oz. of spar with two dwts. of titanium, and heating as above. || Gold mixture is prepared by dissolving 8 grs. of pure gold in aqua regia, and then stirring in 122 dwts. of very finely pulverized spar. When nearly dry, it is formed into a ball fused upon a slide, and then coarsely pulverized. CARVED BLOCK-TEETH. 503 Composition and Preparation of Gum Enamels.—Either of the following recipes will furnish a good gum enamel, and may be used in connection with any of the compositions for body heretofore enumerated:— no. i. xo. n. Gum frit, No. 1, .... 3 dwts. Gum frit, No. 2, .... 3 dwts. Spar,.......9 to 12 dwts. Spar, ......3 to 18 dwts. It is recommended, in order to impart a granular appearance to the gum, to grind the spar somewhat coarsely; any required shade or depth of gum color being obtained by varying the proportions of the frit—the latter containing the coloring in- gredients. Gum frit, No. 1, is composed of felspar, 700 grs.; flux, 175 grs.; oxide of gold, or metallic gold in a state of minute divi- sion, 16 grs. The above are ground in a mortar for five or eight hours, or until they are reduced to an impalpable powder; they are then packed in the bottom of a clean Hessian crucible, coated on the inside with a thin mixture of pulverized silex, and on the outside with kaolin. A piece of tile or slab is then luted with kaolin to the top of the crucible, when it is placed in the fur- nace for from one to two hours, or until complete vitrification is effected. It is then removed, and when cold, the crucible is broken and all traces of adhering silex ground off; it is then broken in pieces and ground until it will pass through a sieve, No. 9 bolting cloth. Gum frit, No. 2, is composed of spar, 700 grs.; flux, 175 grs.; purple cassius, 8 grs. The purple cassius is first thoroughly ground in a mortar, after which the flux is added in small quantities at a time, then the spar in the same manner, grinding until perfect comminu- tion and intermixture of the several ingredients are effected. It is then packed tightly in the bottom of a clean white cruci- ble, the inside lined with silex, and a slab luted to the top, as before, and the whole exposed to a heat sufficient to fuse per- fectly. It is then removed from the fire, and when cold, all foreign substances are ground off and the remaining portions 504 MECHANICAL DENTISTRY'. pulverized until it will pass through a sieve of No. 9 bolting cloth. Having given the composition and mode of preparation of the various compounds which enter into the formation of the body and crown and gum enamels, it only remains to describe the different processes concerned in the construction of porce- lain blocks from the several compositions given, and first of the method of procuring an antagonizing model. Antagonizing Model for an Entire Upper and, Lower Denture Constructed of Block-teetli.—The first step in the process of con- structing block-teeth, for either a full upper set with the natural teeth of the opposite jaw remaining, or for entire dentures for both jaws, is to secure an antagonizing model. For the latter, or complete dentures, above and below, the method does not differ from that employed when single gum teeth are used. A rim of wax is adjusted to each plate in the manner heretofore described, and the plates placed in their proper positions in the mouth; the wax drafts are then trimmed until the exact full- ness and contour of the lips and cheeks are secured and proper relative width is given to the wax rims. Great exactness should be observed in these latter manipulations, inasmuch as the wax drafts are the only guides in the formation of the blocks, both as respects the form and fullness of the arch and the length of the teeth. The proper relation of the two pieces in the mouth is now secured, the wax rims attached to each other, and the median line of the mouth indicated on the wax, and being removed from the mouth, an antagonizing model procured in the same manner as described in a former chapter. Antagrmizing Model for an Entire Upper Denture with the Nat- ural Teeth of the Opposing Jaw Remaining.—A rim of wax, half an inch or more in width, is attached to the ridge of the plate and the latter placed in the mouth. The patient is then di- rected to close the jaws until the cutting edges and grinding surfaces of the teeth of the opposing jaw are fairly imbedded in the wax. The piece is then removed from the mouth and the wax rim detached from the plate by holding the latter for a moment over a spirit-flame. The wax is then placed upon a strip of paper with the side indented by the teeth looking CARVED BLOCK-TEETH. 505 upward, the surface of the wax oiled and a batter of plaster poured upon it, filling the imprints of the teeth and running back an inch and a half or more behind the wax, raising the plaster to a level of half an inch above the wax. When the plaster is sufficiently condensed, it is turned over, the wax re- moved without fracturing the plaster teeth, and a crucial groove made in the' surface of the model posterior to the teeth. This constitutes the lower section of the antagonizing model, and is a representation of the teeth of the lower jaw. The upper section is next obtained in the following manner: A second rim of wax, in width equal to the required length of the teeth, is adjusted to the plate as before and placed in the mouth. The exact contour and fullness of the arch required is then given to the external or labial surface of the wax draft, and the lower edg£ cut away until the required approximation of the jaws is secured, and the points of all the teeth remaining below touch the wax at the same instant. The pa- tient is now required to close the jaws gently upon each other until a slight indentation is made in the wax by the opposing teeth; the me- dian line of the mouth is then marked upon the wax and the plate removed. The plate and wax are now adjusted to the lower section of the model, the points of the plaster teeth being received into the inden- tations in the wax made by the nat- ural teeth. The upper and posterior surface of the lower section of the model having been varnished and oiled, and the exposed surface of the plate also oiled, a mixture of plaster is poured in upon the latter and back upon the model, raising the whole to a level of half an inch above the plate. The two sections, when the latter portion of plaster has consolidated, are then separated, reserving the lower part of the antagonizing model for future use. 506 MECHANICAL DENTISTRY. Forming a Matrix for Molding the Body Prepairatory to Carving the Teeth.—As the process of forming a matrix in which to mold the porcelain paste, giving the general form and outlines to the blocks before carving the teeth, is the same for an upper and lower denture, it will be sufficient to describe the method as it relates to the superior arch. A matrix for an entire den- ture above or below, whether consisting of three, four, or six blocks, is ordinarily made to consist of three distinct pieces independently of the plate and model, and is constructed in the following manner; Three conical-shaped holes are made in the sides of the model, one in front and one on each side, to furnish a fixed articulation for the three sections forming the external walls of the matrix. The appearance of the model when thus pre- pared with the plate and wax rim in place is exhibited in Fig. 370. The sides of the model and external face of the wax are now oiled, and both surfaces covered with a batter of plaster to the depth of a fourth or a half of an inch, extending from the base of the model to the lower edge of the wax, and posteriorly about half-way on each side of the model to form a matrix for the front block, or the two anterior blocks, if the arch is made to consist of more than three sections. Supposing the wax removed from the plate and this front piece in place, the several parts will present the appearance shown in Fig. 371. The plaster rim forming the external wall of the front block being removed, plaster is again added, as before, to the outer surfaces of the model and wax, extending it from the heel of the plate on each side forward an eighth or a fourth of an inch in ad- vance of the posterior extremities of the plaster rim first formed. When hard, the plaster is trimmed even with the edge of the wax draft, and the two pieces removed from the model. The matrices formed by these lateral sections when readjusted to the model with the wax removed are shown in Fig. 372. Having thus provided a matrix determining the general outline and length of the teeth for the entire arch, the wax draft is removed and the plate thoroughly cleansed preparatory to molding the paste—before doing which, however, the line upon the wax indicating the median point of the mouth should be extended across the model. CARVED BLOCK-TEETH. 507 Molding the Porcelain Paste Preparatory to Carving the Teeth.— In the process of constructing an entire denture, it is imprac- ticable, owing to the shrinkage of the body, to form a single Fig. 371. Fig. 372. 508 MECHANICAL DENTISTRY. continuous block or full arch without materially changing its. relation and adaptation to the metallic base, and also to the natural organs in cases where the latter are remaining in the opposite jaw; hence it is customary, as before intimated, to divide the arch into sections—usually three; a central front block embracing the incisors and cuspidati, and two lateral blocks including the bicuspids and molars on each side; or the denture may consist of four blocks, dividing the arch between the central incisors, and also between the first and second bicuspids on each side; making the two anterior blocks to consist each of a central and lateral incisor, a cuspidatus, and anterior bicuspid, and the posterior blocks of the second bi- cuspid and the two molars. Again, the arch is sometimes divided into six blocks—an anterior embracing the central and lateral incisor and cuspidatus, a central comprising the bicus- pids, and a posterior including the molars. If constructed in three sections, as is ordinarily the case, the front block should be molded and carved first. The material for the body, if in a dry state, is mixed with a sufficient quantity of clean rain- water to form a thick batter, and mixed thoroughly in a mor- tar. It should then be poured upon a dry slab of plaster-of- Paris, and when the excess of water is absorbed, removed, and well beaten with a spatula on a marble or porcelain slab until it assumes a somewhat pasty form; it may then be well pressed between folds of cloth to force out any remaining portions of confined air. The plaster rim forming the matrix for the front block is now adjusted in its proper position to the model, and its inner surface, as well .as that of the plate, oiled; the porce- lain paste is then packed into the matrix as compactly as possible, filling it even with the upper edge of the plaster rim. When the paste has been worked in as solidly as possible, pat- ting it with the fingers or suitably formed instruments as suc- cessive portions are added, it should be trimmed even with the edge of the plaster rim and the palatal surface cut away to near the thickness required for the teeth included in the block, leav- ing it somewhat thicker, however, to compensate for the shrinkage of the body, and to allow for small portions which will be cut away in carving the teeth. The plaster rim forming CARVED BLOCK-TEETH. 509 the external border of the matrix is now loosened by tapping gently upon the model and then carefully removed. The mark upon the model showing the mesial line of the mouth and indicating the proper position of the central incisors, is then extended across the block, after which the width of each adjoin- ing tooth is lined off, making each one as much broader than will be required in the finished piece as the porcelain composi- tion will shrink in baking—this, in a block embracing the six anterior teeth, will be equivalent to about one-third or one-half the width of a bicuspid on each side. If the case is one re- quiring a full denture above and below, the operator should next proceed to mold the front block for the lower arch in the same manner as described for the upper. The two sections of the antagonizing model are then placed together, and the proper relative width for the lower teeth indicated upon the inferior block—the drawn lines upon the upper block serving as a guide. The points to which the posterior extremities of the front block extend on each side of the plate should be marked upon corresponding points of the model above and below, to enable the manipulator to determine how far the side blocks should be extended anteriorly when molding the paste for the latter—the marks upon the model being subse- quently transferred to the lower edges of the lateral sections of plaster concerned in the formation of the side matrices. Before removing the front blocks from the plates preparatory to carv- ing the teeth, the surface of the. paste may be dried somewhat by throwing upon it, with a blowpipe, a broad, spreading flame from a spirit-lamp. The blocks are then carefully detached by rapping lightly upon the model, assisted by gentle traction with the fingers. The front blocks being removed from the upper and lower plates, the side sections of plaster concerned in the formation of the posterior matrices are adjusted to the model, and, being oiled, the paste filled in as before described, extend- ing each block forward beyond the point occupied by the cuspi- datus of the front block a distance equal to about one-third or one-half of the with of the latter. These are then cut away even with the edges of the plaster rims and trimmed on the palatal sides, leaving them somewhat thicker than will be re- 510 MECHANICAL DENTISTRY. quired for the bicuspids and molars. The plaster walls of the ma- trices are then removed; the two parts of the articulating model placed together, and the relative width and position assigned to the upper and lower teeth by drawing lines across the exter- nal surface of the blocks. They are then separately removed from the plates in the manner before described, and the neces- sary additional portions of paste added to the grinding surfaces to compensate for the contraction of the body in baking. In constructing a full upper denture with all or a portion of the natural organs remaining below, the proper width to be given to the upper teeth, as well, also, as the required relation or an- tagonism of the artificial with the opposing natural teeth, may be readily determined by applying the lower portions of the antagonizing model representing the teeth of the under jaw, and marking upon each block, as it is being molded, the neces- sary width and position of each tooth above—being careful to make allowance for shrinkage by adding to the length, width, and thickness of each block as much as will "compensate for the contraction of the body. In every other particular, the process is conducted in the same manner as heretofore de- scribed. Carving the Teeth.—The teeth are first separated by drawing between them a thread attached to a small bow, and it may be observed in this connection that the most careful and delicate manipulation is required in handling the blocks while carving to prevent the portions of the paste from crumbling away, a tendency that may be counteracted, in some measure, by moist- ening the paste occasionally with a little water taken up on the point of the carving knife. The general outline of each tooth having been traced upon the exterior surface of the block with the point of the instrument, the operator proceeds next to give the distinct and characteristic form to the crowns, and the har- monious and agreeable effects produced will depend upon the fidelity with which the manipulator copies nature in the form and arrangement of the teeth. The requirements of individual cases are too varied in their nature to admit of specific direc- tions in respect to their formation,—a careful study of the modified forms of the natural organs, combined with some CARVED BLOCK-TEETH. 511 degree of manipulative tact, will enable any one, after sufficient experience, to attain to satisfactory results in this particular. After the teeth are formed, and the body of the block is re- duced to the required thickness, superfluous portions extending from the ends of the block should be cut away, leaving enough, however, projecting to allow for grinding when jointing and adjusting the several blocks to the metallic base. Fig. 373 exhibits the general form of the blocks when carved, showing also the platinum pins, but which are not usually attached to the blocks until after the latter are first biscuited. Crucing, or Biscuiting.—The blocks being carved, are next placed on a fire-clay slab with their palatal surfaces resting on a bed of silex. As soon as the paste has become thoroughly dry, the slab may be gradually introduced into the muffle of a baking furnace, and exposed to a full red heat until semi-fusion of the body takes place. This partial vitrification of the body Fig. 373. serves to agglutinate the particles of the compound, and is termed crucing, or biscuiting. When removed from the furnace, and cool, the platina pins should be introduced into the blocks before applying the gum and crown enamels, and is accom- plished in the following manner: One or two small holes, as the case may require, are drilled into the body of the block immediately behind and below the crown of each tooth, extend- ing about half-way through the block; into these platinum pins or wires are introduced, a head being formed to the end of the pin entering the block. A small portion of the body com- position, mixed with water to the consistence of thin cream, is then worked into the hole around the pin with a sharp-pointed carving knife or camel's-hair brush, its introduction being facilitated by first immersing the block in water immediately before inserting the pins. Application of the Crown and Gum Enamels.—The gum 512 MECHANICAL DENTISTRY. enamel is applied first,* the material being first prepared by mixing the gum composition with sufficient clean rain-water to form a batter of about the consistence of thin cream. This is then taken up with a camel's-hair brush and applied uni- formly to all parts of the external surface of the block repre- senting the natural gum. It should be applied very carefully to the necks of the teeth, forming a neat and well-defined festoon at these points. In applying the crown enamel to the labial surfaces of the teeth, it is customary, in imitation of the natural organs, to so distribute the more positive tints as to give to that portion of the crown representing the neck of the tooth a somewhat yellowish hue, and to the points a grayish- blue tint. To effect this, the material for the yellow enamel, reduced to the consistence before mentioned, is first applied to the necks, uniting it carefully with the gum enamel; and after- ward the grayish-blue to the points, extending it a little below the cutting edges of the incisors, and the cusps of the cuspidati, bicuspids, and molars, giving to the teeth, at these points, a translucent appearance. It is only the external and lateral surfaces of the teeth that are enameled, the palatal surfaces remaining unglazed. The yellow and blue enamels should be so blended when applying them to the crowns that the one shall fade away imperceptibly into the other. Final Baking.—The enameling completed, the blocks are placed upon a bed of silex on a slide, and the latter carefully and slowly introduced into the mouth of the furnace. The fire should then be urged to a clear white heat, and when per- fectly dry, the blocks should be carried with the slide into the body of the muffle, and the mouth of the latter closed tightly with a fire-clay plug. Some knowledge of the requisite degree of heat and time necessary to effect perfect fusion of the ingre- dients composing the blocks is required, and these are ordinarily * Prof. Wilbur F. Litch, in reviewing the previous edition of this work in the November (1880) number of the Cosmos, says : " The author is mistaken in stating that the gum enamel should be the first of the enamels applied after the biscuiting process. On the contrary, it should not be applied until the yellow and point enamels of the teeth are in position and fully carved into shape. The gum enamel is then adapted to the shape of the teeth, and not the shape of the teeth to the gum enamel." CARVED BLOCK-TEETH. 513 well known to experienced block-workmen, but those unaccus- tomed to the process will better determine the completion of the baking by introducing into the muffle along with the blocks a small portion of the body covered with enamel attached to one end of a platinum wire, the other passing through a small stopper fitted to the centre of the plug closing the end of the muffle, and which may be removed and the wire withdrawn from time to time to observe the effect of the heat upon the test-piece. When this is seen to be perfectly fused, as evidenced by a uniform glossiness of the surface, the slab should be drawn to the mouth of the muffle, the draught cut off, and the blocks allowed to cool gradually with the furnace. In place of using a test-piece, however, it will answer the purpose to withdraw the slide to the mouth of the muffle occasionally, where it may be readily inspected and the progress of baking noted. When sufficiently cool to be taken in the hand, the blocks are removed from the furnace. Fitting and Attaching the Blocks to the Metallic Base,—On applying the blocks to the plate, it will be found that a greater or less change of relation between the two has occurred in the process of baking, so that the base of the former will not fit the portion of the plate on which they rest as accurately as when first molded. It will, therefore, be necessary, when adjust- ing each block, to grind away somewhat from the base of the latter until the coaptation of the two surfaces is as perfect as practicable. The several blocks should also at the same time be accurately united to each other laterally, grinding away from the ends, and approximating the sections as the articulation of the opposing dentures may require to effect a proper and efficient antagonism, and which may be determined by the use of the antagonizing model employed in molding the blocks. After the blocks are fitted and the teeth antagonized, and before uniting the former permanently to the plate, a rim should be formed and attached to the borders of the metallic base to form a -socket for the plate extremities of the blocks, and which, extending around the margins of the plate, should be continued across the heel of the latter on each side and made continuous 33 514 MECHANICAL DENTISTRY. with the band of lining on the palatal sides of the teeth. The manner of forming and attaching the rim does not differ from the method heretofore described in connection with full dentures constructed of single gum teeth, to which the reader is re- ferred. The rim fitted, and the blocks replaced, the whole is invested in the usual way, the wax removed from the plate, and a continuous band or lining adjusted to each block. The latter is accomplished by first cutting a pattern of the band from sheet lead of the length of the block, and of the required width, trimming the edge applied to the plate in such a manner that when adjusted to the backs of the teeth it will lie in uni- form contact with the base; this is then pressed against the pins with sufficient force to perforate it. The lead pattern is then placed upon a strip of gold of the required thickness, and the counterpart of the pattern cut from the gold plate, marking at the same time the points to be perforated for the platinum rivets. This is then pierced with a plate punch, and the strip bent to the proper curve and applied to the block, when it is bound to the latter by splitting and spreading apart the ends of the rivets. A band is thus applied to each block. Solder is then applied along the joints, and over the pins, and all parts united with the blowpipe in the usual manner. The piece is then finished up the same as ordinary gold work. Fig. 374 exhibits a palatal view of an upper set of block-teeth mounted on a metallic base. When skillfully executed, the finished work presents a beautiful and highly artistic appear- ance. The application of sectional porcelain blocks to the necessities of mechanical practice has been greatly extended in connection with the vulcanite and celluloid bases, and, to a limited extent, with other processes. Their construction, how- ever, is modified somewhat by the requirements of these special processes, and as made for the latter are of such ap- proved manufacture, and are supplied in such abundance and at so reasonable a cost by all the principal dental furnishing establishments, that the general practitioner, we apprehend, will ordinarily find it more convenient and economical to purchase rather than manufacture them himself. CARVED BLOCK-TEETH. 515 The subjoined account, descrip- tive of a new method of making block-teeth, by Dr. William Calvert, was inadvertently omitted in the first two editions of this work. The process has received marked com- mendation by competent persons who have investigated its merits, and will be highly esteemed by those who desire to excel in this beautiful but difficult art. " The first preparatory step to be taken, after having correct articulating models, is to select single teeth so defined as may either suit the taste of the operator or the peculiarity of the case, and supposing the case to be an upper denture, it will be necessary to have two front and two lateral incisors, two canine or cuspids, two bicuspids (or, if more convenient, the cuspids), and four molars, all of which should be sufficiently large to compensate for shrinkage in the material of which the teeth are to be composed. " The plate upon which the blocks are to be made, and to which they are to be subsequently fitted, being upon its cor- responding model, a rim of wax may be placed upon it, and the teeth arranged upon the wax, articulating with the antago- nizing model, allowing sufficient in the length of the teeth for shrinkage. Beginning with the front incisors, the teeth should be set to the wax (as above) as far back on each side as the first bicuspids, inclusive; then leaving a space equal to the width of. half a tooth, the arch may be completed by the addition of the molars, two on each side. The teeth having been thus arranged upon the wax, with reference to regularity or irregu- larity, height, etc., the desired outline of gum may be filled up with wax. " Special care is requisite in so trimming the wax where joints are contemplated, that no subsequent alteration will be needed during the further manipulations. " It will be necessary, previous to making the molds, to make some provision for replacing them, after they have been once removed, so that they shall occupy the same position as they Fig. 374. 516 MECHANICAL DENTISTRY. did previous to their first removal. For this, it will be only necessary to make some conical holes in the face of the cast, say two on each side, between the centre and the first bicuspid teeth, and two opposite the molar teeth of each side. These holes need not be more than about a quarter of an inch deep, and should be but a short distance below the edge or line of the plate. The face of the cast, including said holes, should now be varnished, when the case is ready for making the molds. " The first mold to be made should be that including the four incisors, two canine, and two first bicuspids, eight teeth in all. This may be done by simply oiling the face of the teeth, outline of gum, and plaster cast, and pouring plaster-of-Paris of a proper consistency over the surface of the same, allowing it to fall slightly over the cutting edges, so as to form a more perfect mold. This mold should be divided in the centre, making two sections, which can be done by cutting through the plaster while in the state of hardening ; or, what is perhaps better, before applying the plaster, make an incision in the wax outline of gum, in which place a thin slip of sheet lead, letting it extend a little above the cutting edges of the teeth, and as far down the face of the cast as is desired to extend the mold. When hard, remove from the cast and teeth, and we have the untrimmed mold for said eight teeth. Previous to making the molds for the back teeth, it is necessary to remove the first bicuspids, or the cuspids representing them, from the position they occupied in making the mold just described, and placing them beside the first molars so as to represent the second bicuspids. Care is to be taken in removing and re- placing them, so that the original form of the wax may be preserved, otherwise the end thereby intended to be secured will be defeated, and the joints at these points will be irregular and unsightly. " For the purpose of rendering clear a point necessarily left somewhat obscure in the foregoing description, it may be well here to state that the space of half a tooth, left between the first bicuspids and the first molars, is to compensate for shrinkage in the length of the arch, for after the first bicuspids are re- moved and set adjacent to the first molars, thereby represent- CARVED BLOCK-TEETH. 517 mg the second bicuspids, they occupy the entire vacancy first left and one-half the space formerly occupied by said first bicuspids ; hence the extension of the back molds toward the centre is equivalent to the shrinkage of the entire arch. " As the foregoing is applicable where the case of fourteen teeth is to be divided into four blocks, as is usual in soldering, I would say that when the intention is to make pin-holes for riveting, the space of half a tooth must be left between the canine and bicuspids, instead of between the bicuspids and molars. " The molds for the back teeth may now be made in the same manner as those of the front ones. After the molds have been made as already described, they should be so trimmed that in the process of molding the blocks there would be no liability of removing portions of the enamel off the teeth in withdraw- ing the molds. The molds should now be varnished with some spirit varnish, and after it becomes dry are ready for use. " The molds being prepared, the next step is the enameling of the teeth in the molds. The enamels should be moistened with a little clean water, and having previously oiled the section or sections of the mold, the blue or point enamel may be first applied (as stiff as it will work) with a very small spatula made for the purpose. This enamel should be thin at the base, and gradually thickening with the concavity of the mold to the cutting edges of the teeth. The yellow or base enamel is next applied heavy at the base, and gradually terminating near the point. " After the enameling has been completed so far as is designed to be molded at one time, a small quantity of the body about the consistency of a thick paste may be spread over the surface of the molds and of the enamels, the molds re- placed upon the model, and the body carefully filled in, at first rather soft, but subsequently harder and harder, until the mold is sufficiently full. Then applying the flame of a spirit- lamp for a few minutes with the blowpipe, the body will be toughened enough to work well, when the molds may be removed. The teeth may then be separated and trimmed, the blocks divided as desired, the gum enamel applied, etc., and so completed. 518 MECHANICAL DENTISTRY. " The process of enameling and molding being precisely the same with all the blocks, it needs not that I should go into further detail. " I have already said, that when the blocks are intended to be riveted upon the plate, the molds are required to be some- what different. There is also another difference; that is, the molding of the pin or rivet holes, which may be done by re- moving the plate from the model, placing the molds upon the model, and drilling a small hole upon the prominence of the ridge opposite the centre of each tooth, in which insert a piece of wire of a desired size. The enameling, etc., may then be done as before described, and after the body has been hardened sufficiently, the pins may be removed, leaving the holes neatly molded, perfectly smooth, and straight. The blocks may then be finished at once, before removing from the cast." CHAPTER XV. UNITING SINGLE PORCELAIN TEETH TO EACH OTHER AND TO A METALLIC BASE WITH A FUSIBLE SILICIOUS COMPOUND, FORM- ING A CONTINUOUS ARTIFICIAL GUM.* The process of uniting single mineral teeth to each other and to a metallic base by means of a porcelain cement was attempted as early as 1820, by Delabarre, of Paris, France, but with such imperfect and unsatisfactory results as induced its early aban- donment. At a later period, Dr. John Allen, a distinguished practitioner of dentistry in America, devised a method embrac- ing original and important modifications of practice both in the preparation and combination of materials, and the modes of manipulating them; and after an extended series of experi- ments, commencing in 1844, succeeded in obtaining certain mineral compounds which vitrified at a heat much below that employed by Delabarre, and the contraction of which corres- ponded so nearly with that of the platinum base to which it was applied, that the shrinkage incident to baking conflicted in no material degree with the practical utility of the work in the mouth. * The attentive reader of the first edition of this work will not fail to note that the statements involving the question of priority, contained in the intro- ductory portion of the above chapter, are at variance with those originally published. A more extended examination and careful analysis of the evi- dences as they appear upon record—evidences not fully accessible to the author at the time of the publication of the first edition—established beyond reasonable doubt the just claims of Dr. Allen as the originator of that special and distinct- ive method here considered, by which the attachment of the teeth to the plate is effected by direct fusion of the gum material. Dr. Hunter's earliest and con- temporaneous experiments contemplated simply a union of all the teeth by means of a fusible cement, forming a single, continuous block, which was after- ward united to the base by riveting or soldering. This brief explanation is here introduced as an act of simple justice to Dr. Allen who has devoted the best energies of his life to the successful develop- ment of a process which stands unrivalled in all the chief requisites of an artificial denture.' 519 520 MECHANICAL DENTISTRY. In the construction of dentures upon this principle, plain single teeth, made for the purpose, are arranged and soldered to a plate properly fitted to the mouth, after which different mineral compounds, made to represent the natural gum tissues, etc., are applied to the plate and teeth in a plastic state, then carved and trimmed in proper form, and by means of a strong furnace heat these compounds, called the body and the gum enamel, are fused, producing a 'continuous and seamless artificial gum and palate undistinguishable from the natural structures. The compounds at present employed in this process, as well as the more fusible preparations used for repairing purposes, are manufactured in quantities sufficient to meet the wants of the profession, and may be procured at all the dental furnishing houses throughout the United States. The intimate but later identification of Dr. W. M. Hunter with the above process has rendered his name familiar as one whose skill and devotion to this specialty of mechanical prac- tice has contributed to its development in a modified form. Dr. Hunter's formulas, and modes of manipulating his compounds, will be introduced hereafter. Following Dr. Hunter's descriptions, the reader will find practical and valuable instructions in this method of substi- tution contributed, at the solicitation of the author, by Dr. S. P. Haskell, of Chicago, 111., Professor George S. Field, of Detroit, Mich., and Dr. Ambler Tees, of Philadelphia, Pa., all of whom are recognized experts, and whose long experience and intimate familiarity with the most approved methods of constructing continuous-gum dentures impart special value to the subject- matter of their communications. Before introducing an account of Dr. Allen's modes of pro- cedure, the author would premise that it is unnecessary to repeat in this connection what has already been fully described in regard to impressions of the mouth, or the manipulations connected with the formation of plaster models and metallic swages, these processes being essentially the same as in the con- struction of ordinary gold work. Whenever a rim is to be formed to the border of the plate extending from heel to heel DENTURES WITH CONTINUOUS PORCELAIN GUM. 521 of the latter, and this is to be accomplished by swaging, the model should be shaped as described in connection with Fig. 74. If it is designed to enamel the entire lingual surface of the plate (a method now commonly practiced), the shoulder upon the model should be extended across the heel of the latter from each extremity of the ridge on a line with the posterior border of the hard palate, to form a groove in swaging similar to, and continuous with, that on the outside of the ridge. The edges thus turned in swaging will flare more than is required— the operation must, therefore, be completed by carefully turning them over sufficiently with pliers. In place of swaging the rim, however, it may be formed by fitting and soldering along the border a narrow plain strip of platinum, extending it as before, if desired, across the posterior edge of the plate. Or a triangular piece of wire may be soldered on, beveled somewhat so as to overhang the base slightly, thus forming a shallow groove. The border to the palatal portion of the gum at the heel of the plate is sometimes formed in swaging by adjusting a wire across the heel of the model, which will be transferred to the plate in the form of a ridge. The latter should be raised a line or more from the posterior border of the plate, and should incline gradually to the edge, while the anterior surface should present an abrupt shoulder to the margins of the gum enamel. The process of forming the rim is sometimes deferred until after the first portion of the body is baked, and before the gum enamel is applied. In this case, the borders of the plate, to the depth of from a line to a line and a half, are left uncovered by the body; after the latter has been baked, the uncovered mar- gins are turned over upon the body with pliers and burnisher, and the gum enamel afterward applied flush with the edge or surface of the rim. In whatever way the rim or socket is formed, it is practically of the first importance that the exact dimensions of the plate required should be ascertained before the groove is formed, as it will be impossible to subsequently diminish the extent of the borders without, to some extent, impairing the integrity of the finished work. The mouth, therefore, should be carefully exam- 522 MECHANICAL DENTISTRY. ined, and the precise location, extent, and fullness of the mus- cles and integuments along the external borders of the ridge above and below, the glands underneath the tongue, and the extreme boundaries of the hard palate, carefully noted and ac- curately traced upon the plaster model, to serve as a guide in determining the dimensions of the plate. Additional strength will be imparted to the metallic base by doubling the central portion of the plate as represented in Fig. 356. The following additional remarks on the method by Dr. Hunter are introduced:— " Platina as usually applied I think objectionable, wanting stiffness; my method of using it is similar to that proposed by Delabarre, but possessing greater strength than even his method, and by it can be made as light as a good gold plate got up in the ordinary way. I first strike a very thin plate to the cast, and cut out a piece the size of the desired chamber, taking care not to extend it forward to embrace the palatal artery. Add wax to the plate for the depth of the cavity, diminishing it neatly as it approaches the alveolar ridge. Cement this plate to the cast and take another metallic cast, strike another thin plate over the whole, and solder throughout with an alloy—of gold twenty-two parts, platina two parts—or with pure gold. The chamber thus formed is precisely the same as ' Cleveland's Patent Plate,' but the space behveen the plates, for which he ob- tained his patent, is subsequently filled up, leaving a cavity resembling Gilbert's, but with a sharper edge when so desired. This space is filled up with base and enamel, and gives great stiffness without the ugly protrusion of the struck chamber. The plate thus formed assimilates much more closely to the palatal dome, not interfering with pronunciation; another great advantage gained by it is the impossibility of warping. I say impossibility, because I have submitted plates so constructed to the severest test, and never had them to warp. It is well to rivet the two plates together before proceeding to solder, espe- cially gold plates, and to bring the heat carefully upon them; once prepared there is no danger of change in the succeeding manipulations." The following method of constructing a base-plate, somewhat DENTURES WITH CONTINUOUS PORCELAIN GUM. 523 analogous to that employed by Dr. Hunter, designed especially to secure the maximum of atmospheric pressure in connection with so-called " suction plates," is thus described by the inventor, A. B. Verrier, of England, in the Journal of British Dental Asso- ciation:— " To retain a denture successfully in contact with the tissues of the oral cavity depends upon the accuracy of its adaptation and the consequent exclusion of the atmospheric air from be- tween the gums and base-plate. If we could exhaust the air entirely from between the gum and plate so that the full force of the atmosphere be exerted upon its lingual surface, it would adhere with great tenacity; resisting a strain equal to fifteen pounds to each square inch of its surface. I have devoted time and attention to the construction of dental atmospheric plates, with varied success, but for some time past I have relied upon a style of atmospheric plate especially applicable to the con- tinuous-gum process, possessing many advantages over the ordinary mode of construction. Among these I may mention its freedom from any tendency to warp in the process of firing the gum body or enamels; thorough stability in the mouth, great rigidity under the pressure of mastication; perfect adhe- sion and freedom from any tendency to injure the mucous membrane; its comparative lightness and simplicity of con- struction. I have with me a specimen plate intended for an upper denture in continuous-gum work, made of two extremely thin soft platina plates, united at their margins, and having a slight space between the two throughout the whole extent of their surface. " I always procure models of the mouth in plaster-of-Paris. Before casting the metal dies, a chamber or shield, oval in form, must be molded on the surface of the plaster model, and should not exceed in diameter half an inch, while the thickness should not be more than one-sixteenth. Having decided upon the dimensions of the base-plate, allow an extra width of one-six- teenth of an inch fuller all round, as the edge must be turned up and present an abrupt shoulder to the margin of the gum enamel. The base-plate may now be struck up to the required form, and the edge turned up with a suitable pair of pliers and 524 MECHANICAL DENTISTRY. hammer. Being satisfied with the fit of the plate, secure it to the plaster model with adhesive wax. A layer of very thin sheet wax (not thicker than a threepenny-piece) is now to cover the whole lingual surface of the swaged metal plate to within one-eighth of an inch of its entire border, cutting away the wax plate covering the shield level with its surface, leaving it exposed. The edge of the wax plate in position upon the model should be nicely beveled off at its outer border to a very thin layer. Mold this in sand and procure metal dies. A second plate is now to be struck up large enough to cover the surface of the wax plate and shield, allowing width enough for soldering. The two plates are now to be removed from the plaster cast and thoroughly cleaned by boiling in a weak solution of sulphuric acid and water, washing and brushing with pumice powder in the lathe. Before uniting the two plates, a very few fine holes must be drilled through the side of the shield, struck up in the base or first plate, to prevent the bursting of the compound plate in the process of soldering, and also for the exhaustion of the air from between the plates by the patient when worn in the mouth. The plates forming the compound plate are now to be united with pieces of fine gold around the margins. The fine gold used in soldering should be laid on freely, as the pla- tina absorbs the most of it in the process of firing. If the union of the two plates is perfect when tried in the mouth, adhesion will be so complete as to require a very considerable force to displace it, the more so if the patient be requested to exhaust the air from between the plate by merely closing the mouth and gently sucking it. I do not advise this course, as the adhesion resulting from the pressure of the external atmos- phere upon the whole outer area of the plate in consequence of the partial vacuum created between the plates causes it to adhere with great tenacity." In the several methods hereinafter described, it will be noticed that the older forms of single continuous-gum teeth are used, or those having two plain pins similar to ordinary plate teeth, but somewhat longer. To secure their attachment to the plate, previous to the application of the gum body, these pins are turned down upon continuous platinum bands or DENTURES WITH CONTINUOUS PORCELAIN GUM. 525 single strips adjusted to the teeth and base, and the whole united by soldering. Since the last edition of this work, Dr. C. H. Land, of Detroit, Michigan, has devised an ingenious method of attachment by which the bands or strips alluded to are dispensed with, and which greatly simplifies the operation. The improvement, in its application to continuous-gum work, is in the construc- tion of the teeth, which are provided with three pins arranged transversely in the cervical portion of the tooth,—one in the centre, and one upon either side on the posterior lateral aspect of the cervix, the latter being somewhat longer than the centre pin. The long pins at the side are so arranged that, when the teeth are in position, the lateral pins of all the teeth will cross each other, as shown in Fig. 375. The pins so crossed, and Fig. 375. also the centre pins, are pressed down closely upon the plate, and the whole united to each other and to the base by flowing solder at the points where they cross, and at their line of junc- tion with the base. These teeth are designed more especially for continuous-gum work, but are applicable to dentures attached to gold plates by rubber or celluloid, and may be used also to advantage, in a modified form, in the use of rubber or celluloid alone. The particular advantages claimed for these teeth are, that, in their use in continuous-gum cases, equal, or greater, strength is imparted to a plate made much thinner than those ordinarily employed, say 32 to 33 Stub's gauge, thus materially reducing the weight of the piece, while at the same time they offered 526 MECHANICAL DENTISTRY*. greater facility and certainty in the manipulation of the gum body. It may also be premised, before considering individual methods, that it has not been deemed necessary to encumber a description of these processes by illustrations of the different kind of furnaces used for the purpose. These have been fully represented and described under the head of " Furnaces." Dr. Allen's Methods.—The following descriptions, contributed by Dr. Allen, embrace a clear and concise account of the manipulations practiced by him in the construction of arti- ficial dentures with continuous gums. " The plate or base is formed of platinum, or platinum and iridium. The plate being properly fitted to the mouth, and wax placed upon it for the bite, as in ordinary plate work, the teeth are arranged thereon, with special reference to the require- ments of the case. They are then covered with a thin coating or plaster mixed with water to the consistence of cream. After this has become firmly set, another mixture of plaster and asbestos wdth water, somewhat thicker or more plastic than the first, is placed round on the outside of the previous covering and the plate. A convenient way of applying the second covering is to turn the mixture out of the vessel upon a piece of tin, say four or five inches square, thus forming a cone, upon which the plate, with the teeth upward, is pressed gently down until within an inch or less from the tin. Then with a spatula the mixture is brought up over the teeth, forming an investient that will not crack in the process of soldering. Sand may be used with the plaster for this purpose, but I think asbestos preferable. " When the covering has become sufficiently hard, the wax is removed, and a rim of platinum is then fitted to the lingual side of the teeth, below the pins, and to the base-plate. The pins in the teeth are then bent down upon the rim, and sol- dered with pure gold, or a mixture of gold and platinum, at the same time the rim is soldered to the plate. This rim, which forms the lining for the teeth, is usually about the thickness of the plate upon which they are set, say twenty-eight to thirty; but should the case require more than ordinary strength, a DENTURES WITH CONTINUOUS PORCELAIN GUM. 527 double or triple thickness of rim should be used. This may become necessary in cases where the natural molar teeth are standing firmly in the opposite jaw, and antagonize with the artificial piece, or where from any cause an undue strain is brought to bear upon the artificial teeth. To attain successful results, the dentist must take into consideration all the circum- stances or conditions of each particular case, and then exercise his best judgment in executing the work. " In soldering platinum with pure gold, flat surfaces of this metal should be brought in positive contact, in order to become firmly united. Therefore in mounting teeth upon a plate of this kind the backing or inside rim should be a little wider than the distance between the pins in the teeth and the plate, say from an eighth to a fourth of an inch. This extra width of rim should be bent at right angles along the base of the teeth, so as to admit of being pressed down upon the plate after the rim is adjusted to the teeth, and the pins bent down firmly upon it. In this way flat surfaces of the rim and plate are brought together and soldered. The pins in the teeth are also soldered to the rim at the same time. When the parts are thus united, they will remain so during the subsequent bakings; but if the edge of the rim only is fitted to the plate and soldered like gold or silver work, the subsequent heatings for baking the body and gum will cause the gold to become absorbed in the platinum, and leave the joints not united. It may be asked, Why not use common gold solder for this style of work ? Answer, Because the alloy in the solder will greatly injure the color of the gum enamel in baking. Copper alloy will turn it to a greenish shade, and silver will give it a yellow tinge. Although pure gold requires more intense heat to melt it (being about two thousand degrees) than ordinary gold solder, yet when melted it flows much more freely than the latter. The best way to solder the teeth upon platinum plate is, to place small pieces of gold upon the joints or parts to be sol- dered, with wet ground borax, and then slowly introduce the piece with the investient into a heated muffle, and bring the whole mass up to a red heat; then withdraw it from the furnace, and bring it quickly under the blowpipe to flow the gold. In 528 MECHANICAL DENTISTRY. this way the teeth do not become etched, as they are liable to be if the soldering is done in the furnace. " The piece being soldered and cooled, the covering is removed from the teeth, taking care to preserve the base unbroken for the plate to sit upon during the subsequent bakings of the body and gum enamel. " All particles of plaster or other foreign matter should be removed from the teeth and plate by thoroughly washing and brushing them. It is well to immerse the piece for a short time in sulphuric acid, after which rinse and brush it well with water. This done, a colorless mineral compound, called the body, is applied in a plastic state (with spatulas or small instru- ments for the purpose) to the teeth and plate. It is then carved to represent the gum, roof, and rugae of the mouth, taking care to keep the crowns of the teeth well defined. The piece is then placed on the base upon which it was soldered, and set upon a slide on the apron in front of one of the upper muffles of the heated furnace,—and every eight or ten minutes it should be moved forward into the muffle, say two or four inches -each time, until the piece shall have passed the centre of the same, which should be at a red heat. It is then withdrawn and passed into a lower muffle, where the heat is greater, in which the body soon becomes semi-vitrified, which is sufficient for the first bake. It is then taken out,and (together with the slide on which it was baked) placed in a cooling muffle, the mouth of which should be closed to prevent the change of temperature from being too rapid, and causing the teeth to become brittle. When the piece is sufficiently cool to handle, a second applica- tion of body is made for the purpose of repairing any defects that may have occurred in the baking; this done, the piece is again introduced as before into the upper muffle, then in the lower, allowing the second bake to become a little harder than the first, but not so much as to appear glossy. It is then with- drawn, and cooled as described above. " A flesh-colored compound is then applied, which is called the gum enamel. This is also made plastic with water, and a thin coating is put over the body, and closely packed and carved around the teeth with small instruments made for the DENTURES WITH CONTINUOUS PORCELAIN GUM. 529 purpose,—still taking care to keep the crowns of the teeth clean and well defined. Small camel's-hair brushes are used wet with water, to cause the gum enamel, and also the body, to settle more closely around the necks of the teeth; other brushes are also used dry to remove all particles of body, gum, or other substances from the crowns of the teeth. " After the application of the gum enamel, the piece is again subjected to the heat of the furnace as described for baking the body, with this difference: The heat should be a little greater than for either of the preceding bakes. It should be a strong, sharp heat, in order to produce a smooth, glossy appearance, which is required for the enamel. These different degrees of heat for the first, second, and third baking should be carefully observed for the purpose of getting an even temper in the piece, and thereby preventing it from crazing or cracking in cooling. " The enamel being thoroughly fused, the piece is withdrawn from the heated muffle, and passed into another, outside of the furnace. This muffle should be made quite hot before the denture is placed in it, in order to prolong the cooling process ; for if the piece is cooled too rapidly it is rendered more fragile. It is well to let the case remain in the cooling muffle, with the mouth of it closed, several hours before exposing it to the air. By baking just at night the piece will be in proper condition to finish up the next morning. " The finishing process consists simply in smoothing and polishing the plate, and burnishing the rim. It is then ready to be adjusted to the mouth. In baking, great care is necessary to prevent the piece from becoming gassed. This can be avoided by allowing the gas to escape entirely from the burning coal or coke in the furnace before the piece is introduced into the muffle. The presence of gas is indicated by the blue flame escaping from the coal. When the fire becomes clear, it is then safe to introduce the case to be baked (as before described) into the muffle. Pure anthracite coal is the best for this pur- pose, as it maintains a longer and stronger heat than coke. Bituminous coal is not good for this kind of work unless first converted into coke. " It often occurs that the natural gums will change more or 34 530 MECHANICAL DENTISTRY. less after the teeth are inserted. In such cases a new impres- sion should be taken from the mouth, and a fusible die formed. The denture is then placed upon the die, and it will be seen at once where the change has taken place; then with the piece resting upon the die the artificial gum may be chipped off with a small hammer and chisel. The platinum plate being soft can be refitted to the die very accurately with a burnisher, hammer, and small driver made for the purpose. A new coat of body is then applied where the plate has been refitted, and then baked, cooled, enameled, and baked again,—still observ- ing the same directions as detailed in the management of new pieces. " If the tooth gets broken (a mishap which seldom occurs by use in the mouth), it can be replaced with another, by grinding out the remaining portion of the broken tooth, and the gum which covers the fang, and then fitting a new one in the place. This tooth need not be soldered to the inside rim; it is sufficient to grind a small notch or groove in the enamel which covers the lingual side of the rim for the pin of the tooth to fit into. The pin resting in the groove is covered with the body at the same time it is applied around the base of the tooth, and when this body is baked the tooth will become firmly fastened in place of the broken one. Any number of teeth that may be required can be replaced in this way. If it is desired to change the position of one or more teeth, or to make them longer, this can also be done as described above, with this additional precaution, which is simply to press softened wax upon the inside of the teeth and palatal arch of the denture before the others are re- moved,—this wax will serve as a guide or index as to the rela- tive change to be made, and also to sustain the teeth in place while they are being fitted as desired to the denture. The wax soon becomes hard, and is readily removed as each successive tooth is ground and adjusted in its proper place. " When the teeth are thus fitted with each pin accurately pressed into the groove prepared for it, and the wax being placed upon the inside to support the teeth in proper position,—body is filled in around the base of the new ones, which are carved, trimmed, and brushed, so as to save the crowns of the teeth DENTURES WITH CONTINUOUS PORCELAIN GUM. 531 clean and properly defined. The wax is then carefully removed from the piece, and more body is filled in around the teeth upon the inside,—filling up the grooves over the pins, and then carving, trimming, etc., as before, to give it the desired form. This done, if the teeth are set a little apart, and it is desired to keep them in that position, take a small piece of asbestos and gently press it in between the teeth at the cutting edges; this will prevent them from being drawn together when the body is being baked. The piece is now ready for the furnace, but it should not be baked hard enough to gloss the newly-applied body; it should have more the appearance of Parian marble. " This being done, it is then withdrawn from the furnace and transferred to a cooling muffle as before described. When sufficiently cool, the gum enamel is applied and baked with a sharp heat until it becomes smooth and glossy. To prevent the old gum from bleaching or becoming lighter colored in consequence of repeated bakings, a very thin coating of fresh gum enamel should be lightly brushed over the entire enam- eled surface of the piece. The enamel thus applied should be mixed with water, quite thin, so as to flow evenly over the surface when applied with a camel's-hair brush. This should be done before the last baking, that the whole may be fused at the same time. Experience and judgment are essential requisites in order to produce good practical results. For example, if the carving of the body is not properly done, the form and shading of the gum and roof will not appear natural when the work is finished; if the gum enamel is put on too thick it will produce a dark-red color; if not thick enough, it will be too light; if fused too hard, it will be liable to craze or crack ; if not hard enough, it will be rough or granular; if the piece becomes gassed in baking, it will be porous and of a bluish color. Again, the teeth of different persons vary as much as any feature of the face, and present as great a variety of expressions. Therefore, in the construction of artificial dentures, the dentist should select and arrange the teeth with special reference to each indi- vidual case. The length, size, form, shade, and position of the teeth should be varied to meet all the different physiognomical requirements that occur in dental practice. , 532 MECHANICAL DENTISTRY. " This system also combines with great advantage the resto- ration of the face in cases where the muscles have become sunken or fallen in from the loss of the teeth and consequent absorp- tion of the alveolar processes. Here, again, the artistic skill of the dentist is brought into requisition. He should study the face of his patient as the artist studies his picture, for he dis- plays his genius not upon canvas but upon the living features of the face; and of how much more importance is the living picture, that reflects even the emotions of the heart, than the lifeless form upon canvas. He should know the origin and insertion of every muscle of which the face is formed, and what ones he is to raise, otherwise he will be liable to produce dis- tortion instead of restoration. This improvement consists of prominences made upon the denture of such form and size as to bring out each muscle or sunken portion of the face to its original fullness; and when these are rightly formed they are not detected by the closest observer. There are four points of the face (of many persons) which the mere insertion of the teeth does not restore, viz., one upon each side beneath the malar or cheek bone, and also a point upon each side of the base of the nose, in a line toward the front portion of the malar bone. "The extent of this falling-in varies in different persons, according to their temperaments. If the lymphatic tempera- ment predominates, the change will be slight. If nervous or sanguine, it may be very great. The muscles situated upon the sides of the face, and which rest upon the molar or back teeth, are the zygomaticus major, masseter, and buccinator. The loss of the above teeth cause these muscles to fall in. The principal muscles which form the front portion of the face and lips are the zygomaticus minor, levator labii superioris alaeque nasi, and orbicularis oris. " These rest upon the front, eye, and bicuspid teeth, which, when lost, allow the muscles to sink in, thereby changing the form and expression of the mouth. " The insertion of the front teeth will, in a great measure, bring out the lips, but there are two muscles in the front por- tion of the face which cannot, in many cases, be thus restored to their original position; one is the zygomaticus minor, which DENTURES WITH CONTINUOUS PORCELAIN GUM. 533 arises from the front part of the malar bone, and is inserted into the upper lip above the angle of the mouth; the other is the levator muscle, which arises from the nasal process and from the edge of the orbit above the infraorbitar fora- men. It is inserted into the ala nasi or wing of the nose and upper lip. " The prominences before mentioned, applied to these four points of the face, beneath the muscles just described, bring out that narrowness and sunken expression about the upper lip and cheeks to the same breadth and fullness which they formerly displayed. If skill and judgment have presided over all parts of the operation, the result will be highly pleasing, and of practical utility." * Dr. Hunter's Formulas and Modes of Practice.—The following methods of compounding and applying the gum materials, as practiced by Dr. W. M. Hunter, were taken from his latest pub- lished descriptions in 1852, and have formed the basis, in a large measure, of more modern methods of compounding the silicious materials used in the manufacture of body and gum enamels. The following is a description of the materials and com- pounds employed :— "Silex should be of the finest and clearest description, and kept on hand ready ground, the finer the better. "Fused spar should be the clearest felspar, such as is used by tooth manufacturers for enamels, completely fused in a por- celain furnace, and ground fine. " Calcined borax is prepared by driving off the water of crys- tallization from the borax of commerce, by heating in a covered iron vessel over a slow fire, and it is better to use immediately * Inasmuch as the improvement for restoring the face has been claimed by others, the reader is referred for the evidences establishing the claim of Dr. Allen to priority of invention to the historical record which appears in the old American Journal of Dental Science of 1845. In the published proceedings of the American Society of Dental Surgeons of that year, it will be seen that a medal was awarded to one of its members, inscribed, "Awarded to Dr. John Allen, for his invention for restoring the contour of the face, August, 1845." This, in connection with the fact that no other record upon this subject is found in our dental literature, fixes the date of this improvement. 534 MECHANICAL DENTISTRY'. after its preparation, as it attracts moisture. It should be per- fectly clean and white, and free from lumps. " Caustic Potassa Optimus.—Known also as potassa fusa. "Asbestos.—Take the ordinary clean asbestos, free it from all fragments of talc or other foreign substances, and grind fine, taking care to remove any hard fragments that may occur. " Granulated Body.—Take any hard tooth material (I use the following formula: spar 3 oz., silex 1\ oz., kaolin J oz.) and fuse completely. Any very hard porcelain, wedgewood ware, or fine china will answer the same purpose. Break and grind so that it will pass through a wire sieve, No. 50, and again sift off the fine particles which will pass through No. 10 bolting cloth. It is then in grains about as fine as the finest gunpowder. 11 Flux.—Upon this depends the whole of the future operations, and too much care cannot be taken in its preparation. It is composed of silex 8 oz., calcined borax 4 oz., caustic potassa 1 oz. Grind the potassa fine in a wedgewood mortar; gradually add the other materials until they are thoroughly incorporated. Line a Hessian crucible (as white as can be got) with pure kaolin, fill with the mass, and lute on as a cover a piece of fire-clay slab with the same. Expose to a clear, strong fire in a furnace with coke fuel for about half an hour, or until it is fused into a transparent glass, which should be clear and free from stain of any kind, more especially when it is used for gum enamels. Break this down, and grind until fine enough to pass through a bolting cloth, when it will be ready for use. uBase.—Take flux 1 oz., asbestos 2 oz., grind together very fine, completely intermixing. Add granulated body 1J oz., and mix with a spatula to prevent grinding the granules of body any finer. "Gum Enamels.—No. 1 Flux 1 oz., fused spar 1 oz., English rose 40 grains. Grind the English rose extremely fine in a wedgewood mortar, and gradually add the flux and then the fused spar, grinding until the ingredients are thoroughly in- corporated. Cut down a large Hessian crucible so that it will slide into the muffle of a furnace, line with silex and kaolin each one part, put in the material, and draw up the heat on DENTURES WITH CONTINUOUS PORCELAIN GUM. 535 it in a muffle to the point of vitrifaction, not fusion, and with- draw from the muffle. The result will be a red cake of enamel, which will easily leave the crucible, which, after removing any adhering kaolin, is to be broken down and ground tolerably fine. It may now be tested, and then (if of too strong a color) tempered by the addition of covering. This is the gum which flows at the lowest heat, and is never used when it is expected to solder. " No. 2. Flux 1 oz., fused spar 2 oz., English rose 60 grains. Treat the same as No. 1. This is a gum intermediate, and is used upon platina plates. " No. 3. Flux 1 oz., fused spar 3 oz., English rose 80 grains. Treat as the above. This gum is used in making pieces intended to be soldered on, either in full arches or in the sec- tions known as block-work. It is not necessary to grind very fine in preparing the above formulas for application. " Covering.—What is termed covering is the same as the for- mulas for gum, minus the English rose, and is made without any coloring whatever when it is used for tempering the above gums which are too highly colored, and which may be done by adding, according to circumstances, from 1 part of covering to 2 of gum, to 3 of covering to 1 of gum, thus procuring the desired shade. When it is to be used for covering the base prior to applying the gum it may be colored with titanium, using from two to five grains to the ounce. "Investient—Take two measures of white quartz sand, mix with one measure of plaster-of-Paris, mixing with just enough water to make the mass plastic, and apply quickly. The slab on which the piece is set should be saturated with water, to keep the material from setting too soon, and that it may unite with it. " (ement.—Wax 1 oz., rosin 2 oz. The proportions of this will vary according to the weather; it should be strong enough to hold the teeth firmly, and yet brittle enough to chip away freely when cold. A little experience will enable any one to prepare it properly." Inasmuch as the method of constructing the platinum base, with Cleveland's modification of chamber as described by Dr. 536 MECHANICAL DENTISTRY. H., has already been introduced, this portion of the description is omitted in this connection. "After the plates are perfectly adapted to the mouth, place wax upon each, which trim to the proper outline as regards length and contour of countenance, marking the proper occlu- sion of the jaws and the median line. These waxen outlines are called the drafts, and are carefully removed from the mouth, and an articulator taken by which to arrange the teeth. " When the absorption is considerable and the plate, in con- sequence, is rather flat, it is necessary to solder a band or rim along the line where the upper draft meets the plate, about one- sixteenth or one-eighth of an inch wide, and fitting up against the outline of the draft. When the ridge is still prominent, the block will not, of course, be brought out against the lip so much, and a wire may be soldered on instead of the wider band. I think one or the other necessary, as it gives a thick edge to the block, rendering it far less liable to crack off than if it were reduced to a sharp angle; it also allows the edge of the plate to be bent in against the gum, or away from it, as circumstances may require, and affords in many cases a far better support for the plates than can be given to one in which the band is struck up, or the edge turned over with pliers, where the block must extend to the edge of the plate. Some few cases do occur when the band may be struck as far back as the bicuspids with ad- vantage, and,some in the lower jaw where it is necessary to solder on the band, but the general practice is not so. " The upper teeth are first arranged on the plate antagonizing with the lower draft, supported by wax or cement, or both. Then remove the lower draft and arrange the lowrer teeth so that the coaptation of the cutting edges of the teeth shall be perfect as desired. The patient may now be called in again, and any change in the arrangement made to gratify his or her taste or whim. Now place the plates with the teeth thereon on their respective casts, oil the cast below the plate and apply plaster-of-Paris over the edge and face of the teeth and down on the cast, say an inch below the edge of the plate. This will hold them firmly in their place while you remove the wax and cement from the inside, and fit and rivet backs to the teeth. DENTURES WITH CONTINUOUS PORCELAIN GUM. 537 When backed, cut the plaster through in two or more places, and remove. Clean the plate by heating. Cut the plaster so that while it will enable you to give each tooth its proper posi- tion, you can readily remove it from the teeth when they are cemented to the plate. Adjust the sections of plaster and the teeth in their proper positions. The plaster may be held by a piece of soft wire. Cement the teeth to the plate and strengthen the cement by laying slips of wood half an inch long along the joints and against the teeth. (I generally use the matches which are so plenty about the laboratory.) Remove the sections of plaster, being careful not to displace any of the teeth. If it be intended to cover the strap with enamel, you should solder a wire after backing, and previous to replacing the teeth, along the plate parallel with the bottom of the straps, and about one- eighth or one-fourth of an inch from them. " The teeth are now backed and cemented to the plate, and present an open space between the plate and the teeth, which is to be filled up with the base, using it quite wet to fill up the small interstices, filling in the rest as hard and dry as possible. Fill the cavity between the plates in the same manner, and oil the edge. Oil the surface of the base, envelop in the investient (precisely as you would put an ordinary job into plaster and sand for soldering) and set on a fire-clay slab previously satu- rated with water. When hard chip away the cement, cooling if necessary with ice, until it is perfectly clean.. Along the joints place scraps and filings of platina very freely, and cover all the surface you wish to enamel with coarse filings, holding them to their place by borax ground fine with water. Apply pure gold as a solder quite freely, say two dwt. or more to a single set. Put in a muffle and bring up a gradual heat until the gold flows freely, which heat is all that will be needed for the base; withdraw and cool in a muffle. Remove the investient and fill up all crevices and interstices not already filled, with covering No. 2 ; cover the straps and base with the same, about as thick as a dime, and cover this with gum No. 2 about half that thickness. At the same time enamel the base in the cham- ber, and cover with thick, soft paper. Set the plate down on the investient on a slab, with the edges of the teeth up. Fuse 538 MECHANICAL DENTISTRY. in a muffle, and the work is completed. Blemishes may occur in the gum from a want of skill in the manipulation; should such occur, remedy by applying gum No. 1. " Should the patient object to the use of platina as a base, the work can be made as above on an alloy of gold and platina 20 carats fine, and soldered with pure gold, etc., as above. In all cases, however, where it is used, the upper plate should be made as I have described above, but with platina any kind of plate can be used. " Ordinary Alloy.—Blocks may be made and soldered 'to the ordinary plate if the absorption is sufficient to require much gum, without any platina. Arrange the teeth on wax on the plate, fill out the desired outline of gum, and apply plaster one- fourth of an inch thick over the face of the teeth, wax and cast. When hard, cut it into sections (cutting between the canines and bicuspids), remove the wax from the plate and teeth, bind the sections of the plaster mold thus made to their places with a wire, oil its surface and that of the plate, fill in the space be- neath the teeth with the base, wet at first, but toward the last as hard and dry as possible, and thoroughly compacted. Trim to the desired outline on the inside, oil the base, and fill the whole palatal space with investient, supporting the block on its lingual side. Remove the plaster mold, and cut through the block with a very thin blade between the canines and bicuspids. Take the wlrole job off of the plate, and set on afire-clay slab with investient, the edges of the teeth down; bring up the heat in a muffle to the melting-point of pure gold. When cold, cover and gum with No. 3 gum and covering. " Another mode is to back the sections with a continuous strap (using only the lower pin), fill in the base from the front, use covering and gum No. 3, finish at one heat. When the blocks are placed upon the plate, the other pin is used to fasten the gold back, which is soldered to it and the platina half-back ; neither of these backs need be very heavy, as soldering the two together gives great strength and stiffness. Very delicate block- work can be made in this way, and it is applicable also where a few teeth only are needed. " A very pretty method, where a section of two or four teeth DENTURES WITH CONTINUOUS PORCELAIN GUM. 539 (incisors) is needed, and only a thin flange of gum, is to fit gum teeth into the space, unite by the lower platina with the con- tinuous back, and unite the joint with gum No. 3. A tooth left ungummed by the manufacturer would be best for the purpose. The same may be applied to blocks for a full arch, remembering not to depend entirely upon platina backs. " The method I prefer for full arches on ordinary plate, is to take a ribbon of platina, a little wider than the intended base, and of the length of the arch, cut it nearly through in five places, viz., between the front incisors, between the lateral inci- sors and canines, and between the bicuspids. Adapt it to the form of an alveolar ridge with a hammer and pliers, and swage on the plate along where the teeth are to be set. Solder up the joints with pure gold, and proceed to back the teeth, etc., as be- fore ; making preparations for fastening, and removing the slip of platina from the gold plate before enveloping in the inves- tient, when proceed as before. " When the teeth are arranged, insert four platina tubes, about one line in diameter, two between the molars, and two between the cuspidati and bicuspids, and solder to the platina base. These are designed, after the teeth are finished, to be the means of fastening to the gold plate, either by riveting in the usual way, or by soldering pins to the gold plate passing up through the tubes, fastening with sulphur or wooden dowels. By these methods we are enabled to readily remove the block and repair it, should it meet with any accident, and also, in case absorption should go on, to restrike the plate, or to lengthen the teeth. The rim should be put on the gold plate after the block is finished; it gives great additional strength and a beautiful finish. " Memoranda.—In preparing material always grind dry, and the most scrupulous cleanliness should attend all of the man- ipulations. In all cases where heat is applied to an article in this system, it should be raised gradually from the bottom of the muffle and never run into a heat. Where it is desired to lengthen any of the teeth, either incisors or masticators, or to mend a broken tooth, it may be done with covering, properly colored with platina, cobalt, or titanium. 540 MECHANICAL DENTISTRY. " In preparing a piece of work, wash it with great care, using a stiff brush and pulverized pumice-stone. Bake over a slow fire to expel all moisture, and wash again, when it will" be ready for any new application of the enamel. Absorption, occurring after a case has been some time worn, by allowing the jaws to close nearer, causes the lower jaw to come forward and drive the upper set out of the mouth. By putting the covering on the grinding surface of the back teeth in sufficient quantities to make up the desired length, the coaptation of the denture will be restored, and with it the original usefulness. " Any alloy containing copper or silver should not be used for solder or plate, if it is intended to fuse a gum- over the lin- gual side of the teeth, as it will surely stain the gum. Simple platina backs alone do not possess the requisite stiffness, and should always be covered on platina with the enamel, and on gold with another gold back. In backing the teeth, lap the backs or neatly join them up as far as the lower pin in the tooth, and higher if admissible, and in soldering, be sure to have the joint so made perfectly soldered." Dr. Haskell's Meth-ods.—" It should be borne in mind that the strength of this work depends mainly upon the metal, and not upon the porcelain, though the latter adds to its strength. While platinum is a very soft metal, yet, by means of various devices, the plate, with the teeth properly soldered on, and ready for the porcelain, can be made very' stiff and strong, therefore everything that can be done to secure a strong foun- dation should be carefully observed. " The plate should be of the best French material (not re- melted scraps and old plates), 29 to 30 gauge for the upper, and 26 to 28 for the lower, and. should be swaged on Babbitt metal dies. The plate is then tried in the mouth, and if the fit is found to be correct, arrange the articulating wax, secure the ' bite,' and make the articulating model. " The back of the plate should be doubled, for the following reasons: It imparts increased strength ; leaves some margin for change, in case of necessity, after the work is in the mouth; protects the edge of the porcelain ; and admits of a neater finish. This ' doubler' should be about three-sixteenths of an inch DENTURES WITH CONTINUOUS PORCELAIN GUM. 541 wide, with the edge turned up slightly to receive the porcelain. Around the outer edge, solder a flattened wire, one-sixteenth, or less, of an inch wide, and 22 gauge, bringing the ends to meet the turned edge of the doubler. This strengthens the plate, and affords a good round finish to the edge, as well as protec- tion to the porcelain. This is easily put on after a little prac- tice, and is far preferable to turning the edge of the plate with pliers, or otherwise. Pure gold should always be used for sol- dering, and with just enough borax (using very little) to give direction to the flow of solder. " Then comes the arrangement of the teeth, and this should always be done in the mouth, the articulating model being only a preliminary guide ; for by the mouth alone can one deter- mine the correct expression and arrangement desired; and it is just here that three-fourths or more of the artificial dentures fail in an utter lack of artistic skill. In this work there is ample opportunity for the display of taste and skill, so that perfection itself is attained at the hands of the true artist. " The investing process comes next. First, a coat of shellac over the teeth to prevent etching (although, if this occurs, it is not a matter of much account, as the baking remedies it). Then a thin coat of clear plaster; next plaster and asbestos, one part of the latter to two of the former. Let the portion under the plate extend at least one inch back of the latter, as this bottom portion is to be retained to bake the case on ; invest the whole one-half inch thick. Warm the case until the plate is suffi- ciently heated to remove the wax easily ; dash boiling water over it (this is the best method to remove wax adhering to teeth and plate in all kinds of work). The backings should be continuous and be lapped on to the plate, for in this is the main stay of the work for strength. Cut patterns in tin or lead, three pieces, one for the six front teeth, and one for each side, lapping over the eye-teeth; the foot-piece should lap on to the plate about three-sixteenths of an inch. No borax is needed. The gold should be melted and rolled into a ribbon as thin as pos- sible, and cut in small pieces and laid under the lap, or foot- piece, and a piece under each pin. The backings can be fitted more easily by splitting the foot-piece. The most convenient 542 MECHANICAL DENTISTRY. method of soldering is in the furnace, being careful not to let it remain too long, so as to fuse the enamel on the teeth. If a pin should fail to solder, it is not material, as the ' body ' will hold it. "After cooling, remove the plaster, and save the base. If any teeth are etched, sandpaper them and remove every particle of plaster; with a sharp instrument scarify the surface of the plate. Place the plate on the articulating model, and if it fs sprung, press it into place, which is very readily done. " The ' body,' and enamel or gum color, as prepared by S. L. Close, is the only reliable material to be had, as Dr. Allen no longer furnishes it for the trade. Apply the' body ' mixed with water, quite thin, by means of an oval-pointed knife, occasion- ally jarring with handle of spatula, and as the moisture comes to the surface, absorb with a cloth; after it is well filled into all interstices, apply it thicker, jarring, absorbing, and packing hard, until enough is on the outside to produce the proper shape and contour of the lips. Then apply, with the curved point of knife, the body to the lingual side of the plate, same as on the outside, but only a thin coat on the plate. Trim around the necks of the teeth, remove all particles from between with a quill toothpick, and brush all particles off the surface of the teeth and exposed portions of plate, and the case is ready for baking. " The Philadelphia furnace, sold by all dealers in dental goods, we prefer. It is always best to use the largest size, No. 1, yet No. 2 will do if the larger size cannot be had. Be sure of a good draught. The furnace can be used as it comes; a better plan is to knock the bottom out of the lower section, get longer bars, that will extend some distance through the front, the two centre ones at least eighteen inches. Build a hearth, two bricks thick and three feet square; build an inclosure of brick, about twelve inches high, large enough to set the furnace on, and line with fire brick. Provide a sheet-iron cover for the front to close the draught. " In setting the ' muffle,' see that the vent hole in the top is clear; this is for escape of gas that may be in the muffle, and would injure the work. Fasten the front end with fire-clay, but leave the back end free. DENTURES WITH CONTINUOUS PORCELAIN GUM. 543 " The fuel to be used must be anthracite coal, or else coke ; Lehigh, range size, is the best. "A sheet-iron shelf, the edge bent into the space between the furnace and cover, and with a leg riveted to it and resting on the long bars, is needed to set the case on, to heat up and run into the muffle gradually. Set the case ten or twelve inches from.the opening, move forward, every ten or fifteen minutes, a couple of inches, until it is in the muffle; place it within two inches of the back, and close the door. If the heat is right, five or ten minutes will suffice ; still, it must be looked at so as not to get too much heat. This first bake should be only a glaze. Remove to a muffle on the hearth, and close up tight. When cool, place on the model, and, if sprung, press it into place. Next fill up all the cracks with very thin body, jarring with handle of the spatula often, so that the material will fill up thoroughly; then spread on thicker until the proper shape and fullness are secured, trimming around the teeth, and doing as previously described, and bake as before, only more so; it should be glossy. After cooling, the enamel is to be put on the same as the body, applying only a thin and uniform coat. The rugse can be produced in the body or in the gum. The enamel should have a thoroughly glossy appearance when ready to remove from the furnace. Heated cooling muffles are unnecessary, as the case itself will heat the muffle all that is necessary. " Lower sets are better without a binding, as it is sometimes necessary to file or grind away the edge. Use plate No. 8, or even thicker, and solder on the edge a narrow strip, flat. " The case is finished by filing and polishing the exposed metal surface, not doing anything to the upper surface. "A ' defined' air-chamber is rarely necessary,—a Cleveland chamber, never. Raise the plate over the hard palate with a thin film of wax on the plaster cast, chamfering off the edges completely; scrape the plaster model across the back, except right in the centre, according to the softness of the palate. " This work is not advisable for partial sets, except in some partial lower cases where there are no detached teeth. In these cases, the plate should be at least two thicknesses across the 544 MECHANICAL DENTISTRY. back of the front teeth, and resting well up on the necks of the same. " Very few seem to know how to prepare a case for repairing, Invest it in plaster and asbestos at least one-half of an inch deep entirely/ place in the muffle before lighting the fire, and allow it to remain with the door open, as the fire comes up, until it is red hot; then remove, cool, and clean off the plaster thoroughly, preserving the base, and it can be run into the furnace with as little danger of cracking as if it had never been worn. " Grind out the remains of the teeth below the margins of the gum ; select a rubber tooth, as it is easier to get and just as good as one made for this work, filing off the pins; hold with wax until a little plaster and asbestos can be placed over it and the adjoining teeth; remove the wax thoroughly and put on repairing body, and bake; cool, put on the gum, having pre- viously ground off a portion of the old gum if it is a very old case, and put on just a little new, and bake as at first. " If blisters occur, grind into them and fill with body and gum, three to one, press hard, and enamel." Dr. Field's Methods.—" When the platinum has once touched the metal dies, never place it under the blowpipe without its having been thoroughly pickled. This is often neglected, and the consequence is that the plate will become more or less discolored from the absorption, under heat, of the baser metal into the platinum. When the teeth are properly arranged with wax on the plate, as directed by Dr. Allen, invest, but use no sand, simply plaster and asbestos. My reason for this I will give further on. "After the investment has become sufficiently hard to handle, the backings may be adjusted; and here I shall differ some- what with Dr. Allen, for, instead of the continuous backing, I back each tooth separately, and for two reasons, one of which is, that I think my job will be stronger when completed, by allowing the body to be well worked in between, below, and completely around the teeth without a platinum wall, as it were, separating the body on a line running completely around the alveolar ridge, and only just touching over the top of this platinum. DENTURES WITH CONTINUOUS PORCELAIN GUM. 545 " My second reason is that, should the teeth be drawn out of place any, as they are sometimes by the investings cracking and pulling away from the plate, the single backing of each tooth admits of a much easier and more perfect re-adjustment than when the backing is continuous. Make the backings of a somewhat V shape, that is, let them be a little narrower at the top than where they come in contact with the plate; bend up the lower part of the backing to the extent of about one- sixteenth of an inch, and at such an angle that when placed in position behind the platinum pin, to which it is to be sol- dered, it shall fit fairly and squarely on the plate; put in posi- tion and press down your pin on it, first having placed a piece of, say number 20, gold foil, folded two or three times on itself, one-sixteenth of an inch square, against the backing, so that when the pin is bent down upon it, it shall hold it from slip- ping away; then with a pair of ordinary plugging pliers squeeze the foil up to and around the pin ; then place one or two pieces of solder (pure gold) just behind, and close against, the heel of the foot-shaped backing. By placing it here, the danger of it slipping' away when the borax calcines under heat is avoided. The less solder you use, and still have your teeth fastened, the better, for the reason that the gold flowing at a less heat than that required for the fusing of the body, the gold is in a state of fusion when the body has set, and there will be no adhesion be- tween the gold and the body. Now solder as most convenient. I find the Fletcher furnace an admirable contrivance for this purpose, ten minutes being all the time necessary to complete the work. Remove the investing carefully, and preserve it all for future use. The plate is then tried in the mouth, and the teeth nicely adjusted to those with which they are to antago- nize. " Everything is now ready for the first baking. Pour out upon a clean butter plate the amount of body required, into which pour sufficient pure water to make a thin paste, and then begin the work of molding and carving your job by filling in between and under all the teeth, tapping your plate gently from time to time; this will bring the water to the surface and settle the body into every nook and crevice. After each tapping, 35 546 MECHANICAL DENTISTRY. absorb the surface water with a clean napkin; by so doing, you will the better hold the body to its place, and prevent its run- ning where not wanted. Build over the roots of the incisors and cuspids boldly, leaving a corresponding depression between the teeth; thus when the piece is completed, you will have that natural and lifelike appearance as of the roots of the teeth showing slightly through the gum. " Now take that part of your investing material that covered the teeth when the piece was soldered, and grind up fine, and with it make a cushion on the slab that is to hold the case an inch thick; then place your piece on this base, teeth downward, and take a small spatula and work the powdered material well up against the teeth, so that the bearing shall be equal under every tooth; this, if properly done, will prevent any drawing away of the teeth from their proper position, as is frequently the case when the plate is placed in the muffle with the teeth upward, the cause being the shrinkage of the body; and now comes my reason for not using sand in this investing material, viz., the sand acting as a flux would attach itself more or less to the teeth themselves, and I have seen this thing carried so far, when the heat was a little too high, as to solidly fuse teeth and slab together. " The piece is now ready for the first baking, and this should be carried ^ no farther than to shrink the body as much as pos- sible, not going beyond a semi-fuse. After this is completed, and the case cooled, proceed to fill up all cracks and shrinkage by the application of more body, when the case is ready for the second baking. This should be done with the plate reversed, teeth upward, using for a support that part of the investing which came in contact with the platinum, and which should be preserved unbroken. In this second baking of the body, care should be taken that it be not overdone. A piece properly baked will present a beautifully granulated appearance, the tips of the granules sparkling like little dewdrops. Carrying the heat beyond the stage necessary to produce this effect vitrifies the body, thereby very much lessening the strength of the work when completed. " If now it is found that a third body is not required (and it DENTURES WITH CONTINUOUS PORCELAIN GUM. 547 rarely is if proper care has been taken with the work so far, although occasionally it may be necessary), proceed with the enameling as directed by Dr. Allen. Should there be any little rough spots on the teeth, caused by overheating when soldering, paint them over with a little clean pulverized borax mixed with water; this will flow the tooth enamel, and cause them to come out from the muffle as bright and smooth as when they first left the factory. " The work is now ready for its third and final baking, which should be with a quick, sharp fire. When fused, draw to-the front part of the muffle; put in the muffle plug, and then dump the fire, and leave until the furnace is cold; by so doing, the case is well annealed, and all danger of checking the enamel avoided. Twenty or thirty minutes now are all that are neces- sary for what little finishing the plate will require, when it will be ready for the mouth. " Let it be remembered by the beginner that on the carving of the first body largely depends the artistic beauty of the work. Keep your patient's face well before you in your mind's eye, and reproduce in the porcelain all those little minor details which, when properly arranged and blended together, shall so counter- feit nature's handiwork that that of man's can hardly be detected." Dr. Ambler Tee's Methods and Formulas.—"Continuous-gum work is mounted upon a swaged plate of pure platina, about No. 29, American gauge. The lower plate, to insure strength, is made of two pieces soldered together, one being large enough to allow for a rim. In a partial lower set, an additional piece of iridionized platina is soldered to the part covering the lin- gual gums of the remaining natural teeth. Plain teeth, with single long pins, made for the purpose by tooth manufacturers, are soldered to the plate with pure gold (24 c.); which alone is used as a solder in this work, since the copper and silver contained in alloyed gold will discolor the gum enamel. The silicious materials called body and gum enamel are then applied around the necks of the teeth, and upon the lingual portion of the plate, by means of small spatulas, and carved to imitate the contour of the gums. 548 MECHANICAL DENTISTRY. " The investment used for retaining the teeth in position while being soldered, is composed of two parts of plaster and one of asbestos; before applying this, the teeth should be coated with a thick varnish of shellac and alcohol, to prevent the teeth being etched in soldering. The backing is fitted most conve- niently by making it of three pieces; the pins are bent down over it, and soldered with pure gold. After soldering, the in- vestment is removed, and the teeth and plate brushed with soap- suds and powdered pumice-stone and washed off with clean water. The first coat of body is then applied, moistened with clean water to the consistence of soft putty, as a foundation; no effort being made to imitate the contour of the gums; separations, however, are made between the teeth so that the body may fuse around each tooth separately, and prevent it being drawn from position by the shrinkage of the body. It is then fused in the muffle, and placed in a cool muffle for thirty minutes. After adjusting it upon the articulator, it is ready for the second coat of body. In applying this, an artistic effort is made to imitate the contour of the gums; and by making elevations and depressions in appropriate positions, the lights and shades of the natural gums may be simulated; especial attention being paid to the ruga?. This coat is vitrified and not fused. After it is cool and again adjusted upon the articulator, the gum enamel is applied, the spatulas being used for the purpose. It is moist- ened with clean water, a little thinner than the body, and laid on a little at a time, about the thickness of twenty-six plate. This is fused and allowed to remain in the cool muffle for an hour and a half. The platina is then rubbed with pumice-stone, an orange-wood stick being used, and the rim filed, stoned and burnished, when the set will be ready for the mouth. " When a set is to be repaired, the mucus should be burnt off before any fresh body is applied. To accomplish this, it should be invested in plaster and asbestos, and heated to redness over a gas or coal-oil stove, or upon the coals in a range. The in- vestment should then be removed, the set washed with soap-suds and pumice-stone, and again heated to redness upon a slide in the muffle. The new tooth, after being carefully ground against the gum, is held in position by plaster and asbestos on the pal- DENTURES WITH CONTINUOUS PORCELAIN GUM. 549 atine surface, a very small quantity being sufficient; after it has set, gum enamel is worked into the joint at the neck and fused in the muffle. The body and gum enamel are then ap- plied to the palatine surface, after the pin is soldered to the old backing, and then fused. This plan obviates the old method of investing the whole set in plaster and asbestos. " Dr. Allen's formulas have never been published. For many years Dr. S. L. Close, of New York, at one time connected with Dr. Allen, has manufactured the materials for the profession, and these can be relied upon. From time to time, however, materials have been placed upon the market purporting to be Allen's, which have checked very much in cooling." Body and gum enamel for continuous-gum work, the author is informed, are also manufactured by Dr. Tees, according to the following formulas and methods of compounding. He furnishes three shades of gum enamel—pale, medium and dark. The body as made by him is composed of Felspar,........2 ozs. Dental glass,......8 dwts. Kaolin, ........3 dwts. The materials are ground together in a moistened state, in a wedgewood mortar, for about an hour; then dried; again ground for ten minutes, and fused in a crucible in a coke fire, or upon a slide in the muffle. After being pulverized, 2 grains of titanium to each ounce are added and thoroughly mixed. The gum enamel is composed of Felspar,........2 ozs. Dental glass,......10 dwts. Gum frit,.......£ dwt. These materials are ground together in a moistened state, for about an hour, in a wedgewood mortar; then dried, ground again for ten minutes and fused—upon a slide rubbed with fine dry silex—in the muffle of the furnace; again pulverized, and sufficient additional gum frit mixed in with a spatula to give the desired shade. These materials fuse kindly and will not check in cooling. Ajplication of Continuous Gum to Partial Sets.—The following method of constructing partial sets of artificial teeth with con- 550 MECHANICAL DENTISTRY'. tinuous gum is taken from a practical and well-written paper on this process by Dr. W. B. Roberts:— " Partial cases may be made of continuous gum; but the work is so various in its nature, that the dentist must neces- sarily depend much upon his own judgment. Difficult cases will constantly present themselves, that will require the exer- cise of much study and ingenuity; in which the general instruc- tion that can be given in words may be of but little service. The first attempt of this kind in my own experience, was in replacing two central incisors. Taking two continuous-gum teeth, I placed upon them a platinum lining, slitting this down along the edge of one tooth nearly through the piece and up the edge of the other tooth by a parallel cut, leaving the two parts joined together by a narrow slip. This allowed sufficient motion between the teeth, so that they could be adjusted as desired. I then placed a bit of tissue paper on the plaster model, covering the spot to be occupied by the teeth and gum, to prevent the adhesion of the body to the plaster, and holding the two incisors in their places, I worked the body into all the depressions of the gum and around the roots of the teeth. I then removed the whole from the model, and placed the piece in a paste of pulverized silex, or plaster and asbestos, upon a slide, and baked as described for full sets. The little slip of platinum kept the two teeth in place. The work shrunk somewhat; but this was remedied by again placing the piece upon the model with the intervention of tissue paper covered with a thin coating of body. Into this I pressed the piece till it occupied its true place, and then filled in again with more body all the crevices around the roots of the teeth, and rebaked. "After enameling, if the work has been carefully and skill- fully done upon this plan, it will be as fine a piece in appear- ance and fit as can be made. It may then be soldered to a gold plate, and the little strip of platinum between the teeth be cut out. With the body and gum formerly in use many difficulties were often encountered from discoloration of .the gum, or from other injuries incurred in soldering. But with Roberts' material, these are easily avoided, and the piece can DENTURES WITH CONTINUOUS PORCELAIN GUM. 551 be treated the same as a block or single gum teeth. In par- tial sets on entire plates of platinum, I have sometimes found trouble, from the enamel giving way upon the small narrow points that connect the teeth with the plate, by the shock occa- sioned in biting. I have consequently left these points uncov- ered, and used two or three thicknesses of platinum to give greater strength. But where this is likely to occur, gold plates would be preferable, if nicely adapted with single gum teeth, or blocks of continuous gum, as the case might require. I have also applied continuous gum in cases where the natural teeth, from one to five in number, were left in the mouth, by making the plates as in full sets, cutting out around the natural ones, and raising a small bead, or placing a light wire around, about one-eighth of an inch or more from the teeth, against which the gum or body is to be finished. The points around the teeth are to be left free, in order to be burnished down in case of im- perfections caused by the difficulty of obtaining exact impres- sions in these places. In such cases I have sometimes formed a strong standard of several thicknesses of platinum fitting closely against one or more natural teeth, leaving a loophole through which to run a gold clasp for afterward securing the artificial set. " I have also secured the gold to the standard by rivets of platinum, and sometimes by two or three gold screws, not pro- viding, in these cases, the loophole. These methods are to be preferred to using solder for fastening; for, in case of repair, the clasps are easily removed without leaving any foreign sub- stance ; but in case of soldering, however carefully they may be removed, there will remain some alloy, which in the baking heat to which the piece is to be exposed will be incorporated with the platinum. Even so small an amount of silver as may be in gold coin used for solder will communicate a yellowish tinge to the gum, spoiling the whole work. Many operators in their early practice, I doubt not, experienced this result; and learned that no alloys, especially of silver or copper, can be ad- missible for soldering this work. I have tried platinum clasps without success, as no elasticity could be obtained, and therefore would not hold upon the teeth. Another source of mischief 552 MECHANICAL DENTISTRY. may properly be noticed in this place. In baking, especially with a new furnace, or with muffles lately renewed, either at the first or second heat, or it may be in enameling, the piece is sometimes changed in its texture and color, as is supposed by the gases present, and the phenomenon is called gassing the piece. The body becomes porous like honeycomb, and of a bluish color. When this occurs there is no remedy but to place it on the metallic die, remove the whole of the injured part, and replace it with a new coating of body and gum. The teeth are seldom, if ever, thus affected. As a precaution, the muffles should be well ventilated with holes for the passage of the heated air and gases." CHAPTER XVI. VULCANITE BASE. While there are undoubtedly many important uses to which vulcanized India-rubber may be ap'plied in the practical depart- ments of dentistry, and for which it would be difficult to find an adequate substitute, yet there are accumulating evidences lead- ing to the conclusion that its total abandonment, as a base for artificial dentures, by intelligent and conscientious practitioners everywhere, is an event of the not distant future. This anticipated result, in respect of a material which has been almost universally employed as a base for the past twenty years, is assured by the confirmed and steadily increasing dis- trust of its suitableness for the purpose indicated, and the growing tendency in the profession to return to higher and less objectionable forms of substitution as respects both material and construction. While what has heretofore been stated in regard to rubber as a base in former editions of this work reflected, as the author then believed, the estimate of its fitness by the profession gen- erally, so, it is believed, does what is now written embody the present judgment of the mass of enlightened practitioners in reference to its unsuitableness and the necessity of its abandon- ment as a base. While the latter is a consummation " devoutly to be wished," there is warrant for the belief that the time when the use of the vegetable plastics, as a base, will be discarded will be contingent on the introduction of other equally inex- pensive methods of substitution that are wholly free from the confessed and well-grounded objections that attach to both rubber and celluloid. General Properties of India-Rubber.—Caoutchouc, gum-elastic or India-rubber, exists as a milky juice in several plants, but is extracted chiefly-from the Siphonia cahuca, which grows in South America and Java. It is discharged through numerous incisions made in the tree through the bark, and is spread 553 554 MECHANICAL DENTISTRY. upon clay molds, and dried in the sun, or with the smoke of a fire, which blackens it. The juice when first obtained is of a pale yellow color, of about the consistence of cream, and has a specific gravity of about 1.012. In the process of drying, 55 per cent, is lost, the residuary 45 being elastic gum. It immediately coagulates, by reason of its albumen, on the appli- cation of heat, the elastic gum rising to the surface. The specific gravity of the juice is diminished by inspissation, becoming 0.925 when hard, and cannot be permanently increased by any degree of pressure. When once stiffened by cold, or continued quiescence, it cannot be restored to its original condition of juiciness. The inspissated juice, or crude rubber of commerce, is alto- gether insoluble in water or alcohol, but is readily soluble in ether deprived of its alcohol by washing, affording a colorless solution. On evaporation of the ether, the gum resumes its original condition. It swells to thirty times its bulk when treated with hot naphtha, and if triturated in this condition in a mortar, and pressed through a sieve, furnishes a homogeneous varnish employed in the preparation of a waterproof cloth. Caoutchouc is soluble in the fixed oils, but is not readily decomposed by cold sulphuric acid or diluted nitric acid, and is unaffected by either muriatic acid gas, sulphurous acid gas, fluo-silicic acid, ammonia or chlorine, nor is it dissolved by the strongest caustic potash lye, even at a boiling heat, and is therefore highly esteemed as an appliance of the chemical laboratory. According to the experiments of Ure, Faraday, and others, caoutchouc contains no oxygen, as almost all other solid vegetable products do, but is a mere compound of carbon and hydrogen, in the proportion of three atoms of the former to two of the latter. From its property of resisting the cor- rosive action of acid vapors, and its tenacity of adhesion to glass, caoutchouc, when melted, forms a very excellent lute for chemical apparatuses. Such are some of the properties of this remarkable product, the uses of which have been almost immeasurably extended since the first successful efforts to produce artificial induration by Charles Goodyear in 1844. VULCANITE BASE. 000 Compounding Rubber for Dental Purposes. — India-rubber is prepared for vulcanizing by incorporating with it, in varying proportions, either sulphur alone or some of its compounds, sulphur being an essential component of all vulcanizable gum compounds. For dental purposes, the coloring is effected in most preparations by the introduction of vermilion (sulphuret of mercury). These substances, properly combined, are sub- jected to artificial heat for a specified time, producing a hard, elastic, hornlike substance, possessing the qualities of lightness, strength, durability, imperviousness to fluids, insolubility in the oral secretions, unchangeableness in exposure to ordinary tem- peratures, etc. Method of Constructing an Entire Denture in a Base of Rubber.— As the manipulations concerned in the construction of a full upper set differ in no essential respect from those required in the formation of a denture for the inferior arch, except as the two differ in conformation, requiring corresponding modifica- tions of practice which will readily suggest themselves, it will be sufficient to describe the method of constructing an entire denture for the upper jaw. An impression of the mouth is first secured in the usual manner, and, for full sets, plaster-of-Paris is preferable to any other material for the purpose. In all practicable cases the same substance may be employed in cases of partial pieces. As rub- ber, when rendered plastic by heat and subjected to pressure, receives a distinct and perfect impress of the face of the model, it is important that the latter should be as smooth upon its surface, and as free from faultiness of form or surface blemish, as possible. From the impression a plaster model is obtained, and if an air-chamber is required, it may be secured either by cutting out from the impression before filling in with plaster for the model, or it may be raised upon the model after the latter has been separated from the impression. For the latter pur- pose, lead is often used, but sheet tin, cut to the required form, is preferable, as the former leaves a tenacious coating of oxide adhering to the plate. A temporary or model base-plate is next conformed as accu- rately as possible to the face of the model, and for this purpose 556 MECHANICAL DENTISTRY. the prepared gutta-percha is the best, though sheet wax may be used. The former may be softened either by subjecting it to a dry heat until sufficiently plastic, or by immersing it in hot water. The face of the model being previously well saturated with cold water to prevent the wax or gutta-percha from ad- hering, the latter is pressed or molded accurately to the model with the fingers moistened with cold water, heating such por- tions from time to time as do not readily yield to pressure until an accurate adaptation of all portions of the plate is secured; then trim to the required dimensions. Having fitted the temporary plate to the model, it is placed in the mouth with a wax guide or rim attached, when the latter is trimmed to the required width, fullness, and contour, and the "bite" of the under teeth secured; it is then removed and placed in its proper position on the model, and the heel of the latter extended an inch or more posteriorly to form an articu- lating surface for the remaining section of the antagonizing model, the latter being obtained in the manner described in connection with metallic plate-base. The mode of procedure in case of entire dentures for the upper and lower jaws differs in no respect from that practiced when gold or other metallic plate is used as a base. Arranging the Teeth.—Having secured an antagonizing model, the teeth are selected and arranged upon the temporary gutta- percha plate in the usual manner. The porcelain teeth used in this process are more commonly in the form of blocks or sec- tions, although either single gum or plate teeth may be em- ployed. Preference is given to the former, because a fewer number of seams or joints are presented for the intrusion of rubber, which, though forming ever so minute a line of sepa- ration, mars the beauty of the finished work by an unsightly contrast in color with the porcelain gum, and which it is not always possible entirely to exclude. The increased strength of attachment formed by the greater number of pins also renders them more permanent and enduring than single teeth. Teeth made expressly for rubber base were originally manufactured with plain platina pins, longer and heavier than those used in connection with metallic plates (Fig. 376); these, when used, VULCANITE BASE. 557 were curved and pressed together, forming loops or hooks to prevent them withdrawing from the rubber. Subsequently, however, the detachment of the teeth was more securely and certainly provided against by the substitution of headed pins (Fig. 377), which rendered their withdrawal from the rubber Fig. 376. Fig. 377. impossible. For this valuable improvement the profession is indebted to the late Dr. S. S. White, whose genius, enterprise, and intelligence were so long and unceasingly tributary to the needs of the dental practitioner. Attention has already been called to Dr. Land's improvement Fig. 378. in teeth. The form specially adapted to rubber work is shown in the right-hand cut, Fig. 375, and also in the single tooth, same figure. The latest design in the construction of porcelain teeth is shown in Fig. 378. The base of the tooth is countersunk, 558 MECHANICAL DENTISTRY. with headed pins inclosed within the cavity. It is claimed that their close conformity in contour to the natural organs makes them much more acceptable to the tongue than teeth backed in the ordinary manner; renders articulation easier and more distinct, and prevents disclosure of artificiality when the mouth is opened. In addition to these advantages, they allow greater facility of adaptation to the maxillary ridge. They are particularly adapted to rubber base with celluloid facing, or to celluloid base alone. In arranging the teeth, portions of the wax rim are cut away to form a bed for each tooth or block, as the case may be, grind- ing from the base of the latter and from their proximate edges until the proper position is assigned to the teeth, and the re- quired antagonism is secured. The teeth, whether single or in the form of blocks, should be united to each other laterally with the greatest possible accuracy to prevent, as far as practicable, the intrusion of the gum material between them. To further provide against this, various expedients have been resorted to with the view of cementing or packing the joints in order to render them impervious to the rubber. The substances usually recommended for this purpose are, plaster or finely pulverized silex or felspar moistened with dilute liquid silex; os-artificial; soluble glass; gold or tin foil, or fusible metal packed into the joints, etc. Of the more destructible substances mentioned, Professor Wildman very justly observes:* "All of these, in course of time, will yield to the action of the fluids of the mouth; and then the ill-fitted joints will be receptacles for soft particles of food, which will be more objectionable than having them filled with good solid rubber. The best filling is an accurately fitted joint; when so made, if the enveloping plaster is of good quality and properly mixed, and no undue force is used in bringing the section of the flask together, there is little danger of the rubber insinuating itself into the joints." As properly remarked, there is no expedient which will so certainly and effectually exclude the rubber as close-fitting joints, and if the precaution is taken to secure an accurate and uniform coaptation of the ground surfaces where * Instructions in Vulcanite, p. 19. VULCANITE BASE. they unite in front, and the "en- veloping plaster is of good quality and properly mixed, and no undue force is used in bringing the sec- tions of the flask together," there will, at most, be but a very thin film of rubber, nearly imperceptible in the finished work, and wholly so in the mouth. To better effect the object stated, the author has been accustomed, when uniting porcelain blocks, to use a small magnifying glass, which reveals inaccuracies of coaptation not apparent to the naked eye. The teeth having thus been prop- erly united and arranged, the wax rim supporting them on the lingual side should be cut away and carved with heated instruments, especially designed for that purpose, as repre- sented in Fig. 379, until the required form and fullness are obtained, add- ing wax, if necessary, to the palatal portion of the plate, making it just enough thicker than that required in the completed set to compensate for waste in the process of final finishing. Any considerable excess of material should be avoided, since it will not only materially increase the labor of dressing the vulcanized plate, but tend to induce sponginess of the rubber under heat. A rim of wax should also be extended around the front and lateral borders of the plate, overlapping, somewhat, the extremities of the gum portions 560 MECHANICAL DENTISTRY. of the teeth. Wax used for the purposes indicated should be of the cleanest and purest varieties. A set modeled in the manner described will present the appearance repre- sented in Fig. 381. Formation of the Mold or Matrix.—The process having been conducted thus far,—any defects in the arrangement of the teeth having been previously corrected upon trial of the plate in the mouth,—the next step in the operation is the formation of a mold or matrix in which the gum material is packed and pressed preparatory to being indurated or vulcanized. In form- ing a matrix, a vulcanizing flask is used, the various parts of which are separately represented in Fig. 380. The lower Fig. 380. section of the flask, A, is first filled one-half or two-thirds full of plaster mixed with water to the consistence of cream. Into this the base of the model, previously moistened with water (the plate and teeth being attached to the model), is immersed and additional portions of the plaster added, if necessary, filling the cup even with the upper edge, and extending it up the sides of the model to the lower edge of the external rim of wax attached to the borders of the gum plate. The base of the model should be cut away, so that when placed in the flask the lower edge of the gum plate will extend but little above the level of the upper borders of the cup. The surface of the VULCANITE BASE. 561 plaster is then trimmed smoothly, and coated with varnish and then oiled; all the exposed portions of the gum plate and wax are also oiled, leaving the surfaces of the teeth un- touched. The several parts will now present the appearance represented in Fig. 381. The upper section of the flask, B, is next placed in its proper position over the lower—the slides formed in one, and corresponding grooves in the other, deter- mining an accurate relation of the two pieces. Into the upper rim of the flask, plaster, mixed to the consistence before men- tioned, is now poured, filling it completely. The lid or cap, D, also filled in with plaster, is then applied to the opening above, and the several parts of the flask compressed by placing them Fig. 381. within the clamp, C, and forcing them together with the screw, impacting the plaster and driving out the excess through the joints of the flask. As soon as condensation of the plaster takes place, the flask should be placed in a hot-air chamber or on a stove, and heated throughout sufficiently to soften, but not melt, the wax. The clamp is then removed and the two sections of the flask carefully separated by forcing a small chisel-shaped instrument in at different points between them, the lid closing the opening above remaining in place. On separating the flask, the teeth, with the wax and temporary plate, will be found attached to the section of the matrix last formed, the portions 36 \/ 562 MECHANICAL DENTISTRY. of the crowns of the teeth not covered with wax being imbedded in the plaster and their plate extremities presenting toward the the matrix, as seen in Fig. 382. The gutta-percha plate and wax should now be carefully detached with such instruments as will best enable the operator to work out confined portions around the platinum pins and from the interstices between the teeth, being careful at the same time not to deface the plaster surface of the mold. To relieve the matrix more perfectly of all traces of wax not accessible to instruments, the section con- taining the teeth may be subjected to a heat sufficient to induce its complete absorption by the plaster. The flask should be heated gradually, otherwise the contents may be suddenly and forcibly ejected in consequence of the too rapid evolution of vapor. Before packing the material, provision should be made for the escape of any excess when the matrix is filled and the two sections of the flask are forced together, permitting the latter to close upon each other in exactly the same manner as before the introduction of the gum. If the vulcanizable substance be- comes engaged between the surfaces of the plaster around the matrix, the vulcanized base will be increased in thickness just in proportion to that of the interposed layer of gum, and hence the teeth of replacement will be relatively elongated. This increased thickness of the base and consequent changed relation of the teeth to the maxillary ridge and to those of the opposing jaw, if but slight, may be immaterial in the application of full sets of teeth; but it is far different in the construction of partial pieces, where the perfection of the finished work depends in so great a degree upon a faultless preservation of the exact position originally assigned to the organs of replacement in the several vacuities on the ridge. If, for example, in replacing the superior incisors, the approximation of the two sections forming the mold is obstructed by the in rusion of the gum material between the plaster surfaces, the teeth, whether plate or gum, will be relatively elongated in proportion to the increased thick- ness imparted to the base consequent upon the incomplete closure of the flask, and however accurately or skillfully the porcelain teeth may have been originally fitted to the vacuity in front, VULCANITE BASE. 563 the artificial will be found to depart from the natural gum, while the porcelain crowns will be displaced and projected below those of the contiguous natural organs. Such displace- ment in the cases last referred to, however small in degree, can- not fail either to impair or destroy the value, both as respects appearance and utility, of the substitute. The usual method of furnishing an exit to redundant material, is to form a series of conduits or grooves in the surface of the plaster containing the teeth, extending them from the edge of the matrix to the Fig. 382. rim of the cup. The escape of the gum will be facilitated by filing notches at intervals around the rim of the flask, making the grooves in the plaster continuous with them, the grooves being an eighth or a fourth of an inch apart. To still more effectually prevent the intrusion of the vulcanite material be- tween the surfaces of the opposing sections of plaster, a circular groove may be cut in the plaster within a line or two of the margins of the matrix, into which narrow channels at short distances are made leading from the mold; others, again, are 564 MECHANICAL DENTISTRY. made at wider intervals from the circular groove to the outer margins of the flask, terminating as before in small notches formed in the rim of the cup. Fig. 382 exhibits the section of the flask containing the teeth with the channels formed as de- scribed ; the remaining section containing the model is shown in Fig. 383; the two pieces when closed upon each other form- ing the matrix. Into the grooved section of the mold, the vulcanizable substance is packed previous to being indurated. It is at this stage that the materials employed to exclude the rubber from between the teeth, and noticed in another place, are packed into the joints before the gum material is introduced. Fig. 383. The face of the model should also be coated with some sub- stance which will prevent the rubber from penetrating the pores of the plaster, and its adhesion to the surface of the model. Barker's ethereal solution, or the collodion of the shops, may be used for the purpose. Preference is given by Professor Wildman to soluble glass or liquid silex, as being more readily detached from the surface in finishing than the preparations mentioned. The latter should be allowed to dry perfectly be- fore packing. Either of these substances is best applied with a small brush, coating the face of the model uniformly. Packing the Mold,—The portion of the flask containing the VULCANITE BASE. 565 teeth should be first heated in an oven or furnace, or over the flame of a spirit-lamp, until the temperature of the whole is sufficient to render the vulcanizable gum soft and pliable as successive portions are applied and pressed into the mold, and to retain it in that condition until the operation of packing is completed. Narrow strips of the gum material should first be worked carefully into the contracted groove underneath the platinum pins with small curved or straight-pointed spear- shaped steel instruments (Fig. 384), adding on small pieces at a time after each successive portion is thoroughly impacted, until the main groove of the matrix over the base of the teeth is partially filled. The palatal convexity of the mold may then be covered with a single piece cut to the form of the uncovered space; a smaller piece of the same general form as the latter may then be added, giving to the central portion a double thick- ness of the gum-plate material, so that when the two sections of the flask are brought together, the excess of gum in the Fig. 384. centre will be forced gradually to the margins of the mold, diminishing, thereby, the liability of the grooves becoming prematurely clogged with the material before the opposing sec- tions of the flask close upon each other. Especial care should be taken in the process of packing to avoid contact of the in- struments with the surface of the mold, as fragments of the broken plaster are liable to mix with the gum and render the surface of the finished work imperfect by forming small pits wherever such particles occur. In regard to the quantity of rubber necessary to fill the matrix perfectly, experience in its use will enable the operator to esti- mate the capacity of the mold with tolerable accuracy. Some small excess of rubber should always be provided. The required quantity, however, can be more certainly determined by meas- urement or weight. A very simple instrument (Fig. 385), con- trived by Mr. E. T. Starr, may be used to determine the quantity 566 MECHANICAL DENTISTRY. by measurement. The vessel being partly filled with water, the lower point is adjusted and fixed with a screw to mark its height. Into this every particle of the model plate is immersed, and the rise of water indicated in the same manner bj7 the upper point. The vessel is then emptied and well cleansed, clean water filled into the level of the lower point, when rubber Fig. 385. is added in sufficient quantity to bring the surface of the water on a level with the upper point; to this is to be added the necessary excess of rubber before recommended. The following method of determining the quantity of rubber by weight is given by Professor Wildman:— " The specific gravity of wax is .96. I have found that of VULCANITE BASE. 567 the American Hard Rubber Company's prepared gutta-percha to be 2.454, and the same Company's red rubber to be 1.572. Hence, to fill the mold, when pure wax is used for a model plate, it will require to one part of wax, by weight, 1.6 of the Company's red rubber; and when the plate is made of prepared gutta-percha, it will require to one part of it, by weight, .6 of red rubber. When the wax is colored, the disparity in weight will not be so great as with pure wax. " Of the two methods to ascertain the quantity of rubber, that by measure offers an advantage over that by weighing in the facility with which it can be arrived at, especially when Starr's instrument is used, the calculation being based upon bulk only; whilst by weight, when the model plate is composed of more than one substance, as it frequently is, of gutta-percha, Fig. 386. Fig. 387. wax, and sometimes wires introduced to give stiffness, quite an intricate calculation must be made to ascertain the exact quantity." Having completed the packing of the mold, the two portions of the flask are re-applied to each other in exactly their original relation, being careful that the apposition of the two is such that, when approximated, the guides attached to one division of the flask shall pass directly and without obstruction into the grooves or slots in the one opposite. With the flasks first intro- duced, some difficulty and uncertainty were often experienced in effecting the desired closure of the flask on account of inher- ent defects of construction, but more recent improvements have entirely obviated this difficulty. Those manufactured by Drs. 568 MECHANICAL DENTISTRY. Hayes and Whitney enjoy deserved popularity, and are, perhaps, in most general use. Fig. 386 represents one of Hayes's flasks, with improved clamps. The lug-joint is so constructed that the strain all comes upon the casting. The pin only serves to keep the lug in place while not in use. The several pieces all being attached together, are not liable to get lost or mislaid. Whit- ney's flasks, original and improved forms, are shown in Fig. 387. The improvement in construction consists in reversing Fig. 388. the position of the bolts, fitting the head into the hole in the lower part of the flask, and using a nut on top. What is known as the " Starr Flask," highly commended as fulfilling very perfectly the requirements of practice, and as happily meeting some important indications, is represented in Fig. 388. Every operator of experience is familiar with the annoyance and difficulty sometimes attending a satisfactory adjustment of models of unusual depth, often of lower sets, VULCANITE BASE. 569 and partial pieces, where the porcelain teeth are secured by the surrounding plaster to the model—difficulties arising from the shallowness of the lower section of flasks as ordinarily con- structed. The " Reversible Flasks," invented by Mr. E. T. Starr, the different parts of which are represented in the accompany- ing cuts, provides very perfectly for any exigency that may arise in the class of cases mentioned. The following description of this flask is taken from the advertising columns of the Den- tal Cosmos:— " The rings of this flask are of different widths, either of them fitting the top or bottom accurately, as may be required. " By using the wide ring next to the bottom, an admirable Fig. 389. flask is obtained for deep cases and partial sets, or where the artificial gum rests on the natural. The narrow ring is used next the bottom plate, for whole dentures, where the parting is at the rim of the plate. The bottom has three countersunk holes, through which the plaster runs, and, when set, holds the accompanying ring securely to it. The fastenings of the flask are T-shaped at one end, and fit the slots in the bottom plate; and, being free at both ends, are more easily adjusted than or- dinary bolts. The flask being in four pieces (two rings and two plates), the plaster is removed without the usual trouble. The cuts represent the flask in different positions." 570 MECHANICAL DENTISTRY. The author has, for several years, used almost exclusively, and with the greatest satisfaction, a flask constructed with de- tached T-shaped bolts fitting accurately into slots or grooves extending continuously from top to bottom of the flask, as represented in Fig. 389. The closure of the sections by this arrangement, with the bolts in place, is unerring, and is accom- plished with the greatest facility. It is called the " Anchor " flask, furnished by the Philadelphia Dental Manufacturing Fig. 390. Company, but the author is unadvised of the name of the inventor. The " Taylor Improved Flask " is represented in Fig. 390. The posterior and lateral portions of the lower section, having raised margins, gives the section at these points considerable additional depth, a modification of form especially well adapted to lower pieces. Fig. 391 represents an oblong, or " box flask," designed for VULCANITE BASE. 571 exceptionally large cases, splints for fractures, artificial palates, etc. Whatever flask is used, the entire mass of inclosed rubber should be rendered uniformly plastic, after packing, by subject- ing it to either a dry heat, such as may be obtained with a conveniently constructed sheet-iron furnace, the baking apart- ment of an ordinary cooking stove, or any other available means by which a diffused and uniform temperature may be secured, being careful not to overheat; or, if moist heat is em- ployed, by immersing the flask in boiling water for a time sufficient to soften the rubber. The approximation of the sec- FiG. 391. tions of the flask should be effected interruptedly—alternately heating the entire mass and tightening by means of the screw- bolts until all the redundant material is expelled by degrees through the outlets provided for it, and the sections of the flask close accurately upon each other. Another method of introducing the rubber into the mold is that of injecting it into the closed flask by means of a force pump. A device, known as the " Howell Packer," Fig. 392, is used for this purpose. After the mold has been cleared of the base-plate, suitable gate-ways are cut, and the flask is closed. 572 MECHANICAL DENTISTRY. It is then screwed to the nozzle of the force pump, the piston of which is operated by a screw cap which encircles the cylinder of the pump. The flask and pump are then dropped into boiling water, and the piston slowly screwed down until the rubber issues from a small notch in the flask opposite the point of insertion of the pump. The pump is then removed and the opening in the flask closed with a screw plug, when the flask is ready for the vulcanizer. The advantages claimed for this Fig. 392. method of packing the flask are, the very greatly decreased lia- bility of checking or breaking section teeth, when they are used. And in those instances where plain teeth are fitted directly against the natural gum, there is less liability of displacement; and there is no opportunity for the rubber to flow over the bases of the teeth, and derange the articulation, as it sometimes does when the flask is closed in the ordinary manner. VULCANITE BASE. 573 For the foregoing description and illustration of this very ingenious packing device, the author is indebted to the Buffalo Dental Manufacturing Company. Vulcanizing.—The process of vulcanizing or hardening the various rubber compounds employed for dental purposes is effected by subjecting them for variable periods of time to the action of heat, the substances to be acted on being confined within a chamber constructed for the purpose. As introductory to a consideration of the usual methods and appliances employed in the process of vulcanizing, considerable space is given to the following somewhat lengthy abstract of a paper by F. Alb. Boek, of Berlin, Germany, translated by Dr. Louis Ottofy, of Lebanon, 111.* The discussion embodies a some- what exhaustive consideration of the rationale of the process of vulcanizing, and is introduced in this connection not only as a matter of curious scientific interest, but of practical importance in the proper treatment of a plastic material which still con- tinues to be largely used as a base for artificial dentures. The writer says:— " The rubber we use, as is well known, is common rubber mixed with sulphur, to which is added certain coloring mate- rials. Of the latter I will speak later in the course of this paper. Though they may influence the hardening of the rubber indi- rectly, they have no other direct influence. This rubber mixed with sulphur forms our ' dental rubber.' The rubber which we obtain from the dental depots is already ' vulcanized,' as this latter simply means mixing the sulphur. We know that when it is heated it becomes hard. The circumstances under which this takes place leads us to several questions: Is it the heat, or the steam pressure, or the melting of the sulphur, which causes the change in the rubber ? " Formerly, the impression prevailed that the hardening took place from the influence of the steam. In the first vulcanizers the flask stood on a stand in the vulcanizers above the water ; but as once, in 1856, the flask fell into the water, the vulcan- izing took place as usual, the mistake was corrected. Later it was found that the process would take place even if the heat * Missouri Dental Journal, June and August, 1882. 574 MECHANICAL DENTISTRY. was passed through oil or sand, and that the same was the. case with glycerine and paraffine. Certainly, under these circum- stances, the time of vulcanizing was longer than when steam was used; this circumstance, at that time, however, was of no particular consequence, as it took from three to four hours to vulcanize it by steam. I will return to this difference of time later, suffice it to state here that vulcanizing can take place in the absence of steam. " It is clear, therefore, that it is the heat alone which causes the hardening of the rubber. In order to answer the question of why this takes place, it will be necessary to turn into the domain of chemistry. " The rubber is a vegetable product; it is the sap of certain trees, which hardens on exposure to the air. As a vegetable product it is liable to the changes of all other vegetable sub- stances, and all changes which it undergoes are found equally effective on other vegetable substances. From this fact it is very simple to draw conclusions for our purpose. " Chemistry teaches that all vegetable products, such as wood, starch, the leaves and sap of plants, consist of four elements, oxygen, nitrogen, hydrogen and carbon. In no plant, or the product of a plant, is carbon absent, and it is mostly in con- nection with hydrogen and oxygen, whereas nitrogen is but seldom present. From these few elements nature has produced all that the earth possesses of vegetable growth, the variety and difference being sometimes only the different proportion of union of the elements, or the addition of a small amount of acids, bitter substances, coloring matters or salts. Rubber con- sists only of the above elements, namely, C16H7; it belongs, therefore, to the class known as the hydrocarbons, and to that class of these in which C predominates. It is interesting to notice Jiere that the change from the soft to the hard, as is the case with rubber, is the property of all vegetable products. We know that the change takes place by the application of heat, that hydrogen sulphide (H2S) is formed, and that the process takes place during the exclusion of air. This process is chemi- cally the same as takes place in the dry distillation of wood, in the changing of wood into coal, and of resin into amber. If VULCANITE BASE. 575 wood is heated in the open air it burns; the same is the case with rubber, only that the latter burns slower on account of its larger percentage of C. If wood is, however, heated in the absence of air, as is the case in making illuminating gas, quite peculiar substances are eliminated from the wood, the illumi- nating gas, which escapes, and three substances; a watery pyroligneous acid (wood vinegar), a thick viscid liquid (wood tar), and a solid mass (charcoal). " The wood tar is, like the rubber, of a resinous nature; it con- sists of the oil of wood tar and a liquid substance, burnt resin. Both become hard on cooling: the former is the well-known par- affine, the latter the equally well-known pitch. " The rubber undergoes similar changes. If it is heated while excluded from the air, as is the case in vulcanizing, there escapes (as in the case of wood, illuminating gas), the hydrogen sulphide, and there remains a plastic, which hardens on cool- ing, as in the case of pitch or paraffine, and we have our hard rubber. " If we think over this subject, it becomes clear to us why sul- phur is added to the rubber. By dry distillation one or more equivalents of hydrogen separate from the mass and remain gaseous, or unite with other substances present and form a liquid, thus leaving behind a hard substance, which consists mainly of C. It is well known that the hardest substance, the diamond, is pure C. The more equivalents of H that remain, the softer is the substance, as in the following scale: coal, resin, pitch, axle grease, oil, ethereal oils, gases. The same is the case in the reversed order. If, from the soft rubber, hard rubber is to be made, it is necessary to remove from it one or more equivalents of H. This is the case in dry distillation. If there was no dry distillation, if the rubber was heated under free admission of air, the C would immediately unite with the 0 of the air, forming carbonic acid, combustion would take place, even though it would be slow and difficult. That cannot take place when the air is excluded, the carbon remains unchanged, whereas the H finds a substance with which it is more than willing to unite at a high temperature. This substance is the S, and the union of these forms H2S, which is well known to 576 MECHANICAL DENTISTRY. us by its odor. When this union has taken place a chemical change has been accomplished, a new substance has been pro- duced, the gas escapes, the remainder, the product of the distil- lation, contains less H than the raw rubber, and on cooling, like pitch, it becomes a harder substance by its containing more C than before. Hard rubber, therefore, is one step nearer to resin than soft rubber. All resins are, as is well known, invol- atile substances, and they possess the power to prevent other substances from becoming volatile; they are insoluble in water, and, consequently, tasteless; they are soluble in volatile oils, as turpentine oil, benzine, etc. It is known that hard rubber does not only possess these characteristics, but resembles the resins, by its easy electrification, to a remarkable degree. " My hypothesis, therefore, leads me to the following conclu- sion :— " The hardening or, so called, vulcanizing of rubber is the changing of caoutchouc into a resin-resembling substance, by the process of dry distillation, and, namely, by the removal of one equivalent of H. The addition of S serves only as a base, which is indifferent toward C, but unites with the H by virtue of a strong chemical affinity existing between H and S, which form a new compound, H2S, which escapes as a gas. "You will notice I do not agree with the opinion that the sul- phur, by melting and hardening, exerts the influence required to harden the rubber. The hypothesis was laid down in some American Dental Journal, that just as is the case with camphor and celluloid, it is with sulphur and rubber—that is, that the sulphur is the medium which brings the particles of rubber into the plastic condition, and afterward retains them in the hardened condition. " We know that a portion of the original composition of the rubber has disappeared, and we know that some of the sulphur and hydrogen disappear. It is natural that if more sulphur is present than can combine with one equivalent of hydrogen, the remainder is in mechanical union with the rubber. If hard rubber be heated to a degree somewhat higher than the boiling point of water, it loses its hardness. This fact might lead to the conclusion that the sulphur melts, and thus influences the VULCANITE BASE. 577 hardness of the rubber. If, however, the correctness of my theory be granted—that is, that hard rubber is nothing but the resinous state of the original product—we observe that it must soften, as the melting point of the resins is about the same as that of sulphur. Furthermore, we know that sulphur hardens slowly, whereas resins become hard more rapidly, as is the case with shellac and sealing wax; the same is the case with heated hard rubber. Hard rubber, when undergoing the change from its melted condition into the hard condition, does not change the character of its molecular relation, remaining amorphous, resembling in its structural appearance molten glass. All resins, gum, glue, tar, etc., show the same characteristics. Sul- phur, on the contrary, when changing from its molten condi- tion, either crystallizes or becomes crystalline in appearance. " I do not wish to prove anything further by this theory. It may, however, be mentioned, that if it be correct, some import- ant results may be accomplished. I will mention, for one, the fact that the scraps and filings of hard rubber, which are now useless and thrown away, may be made valuable and useful. Lately, a patent has been obtained by which useless vulcanized rubber may be made useful. "Leaving this subject, we now arrive at one not any less important, namely, the influence of steam pressure on vulcani- zation. " It has been previously stated that vulcanized rubber may be hardened without steam. This teaches us that hardening is not produced by steam. The theory which has been discussed gives us the reason. The question arises, Why do we use steam ? The answer is, steam has no direct influence in vulcanizing; it only serves the same as oil, sand, paraffine or glycerine for the transmission of the heat. This takes place by use of steam faster and with more precision and certainty than with other substances. Furthermore, it will be shown further on that for other reasons steam is the best vehicle for the purpose. "As with oil, by using steam, the heat is equally distributed and the temperature rises evenly. Changes of temperature, as is the case in dry vulcanization or over-heated steam, are also prevented. It also has the important advantage of causing the 37 578 MECHANICAL DENTISTRY. hardening to take place more rapidly. This latter fact is known to us by experience, it only remains to explain the reason why this is so. " By the use of steam, hardening takes place in from fifteen to seventy-five minutes, according to the temperature, the quality of the rubber and its thickness; by the use of dry heat or oil the process requires from two to three hours, and the requisite degree of heat must be reached gradually. What is the reason that by the use of steam and a high degree of heat it takes less time to vulcanize ? It must be remembered that the higher the temperature the less time is required to vulcanize. The reason of this is clear, if we remember that, according to my theory, hardening is subservient to the escape of a certain amount of hydrogen from the rubber. " The greater the heat, the easier is the separation of the un- natural union—as it were—of the hydrogen with the carbon of the rubber, and it also facilitates the union of this H with the S, which is in a molten condition. This takes place in accord- ance with the laws of chemical affinity and relation. It is a sort of magnetic power which the sulphur exerts upon the hydrogen, and which becomes firmer and more powerful the higher the temperature. Here the steam does not take any part, as it only does the same thing as oil or sand would do, and that is to transmit the heat. There must be another reason why the use of steam permits us to increase the temperature and shorten the time. We know that we cannot do so when using sand or oil, as in that case the rubber becomes porous. If we can find the reason why the rubber becomes porous, we can ascertain the influence of the steam when used a shorter time. "A great deal has been written and said in regard to the porousness of rubber. This takes place when the escape of the gas is retarded or prevented in certain places. This may take place when the heat was applied rapidly or unevenly, or when it was not equally distributed to all parts of the rubber. In the latter case, such parts as are more exposed to the radiat- ing heat than others, become hard much sooner, because the H escapes quicker. In the former case, that is, by rapid increase VULCANITE BASE. 579 of heat, the outer surface of the rubber hardens sooner than the inner, to which the heat only reaches gradually. Rubber is, as is well known, the poorest of conductors. It is clear, therefore, that the thicker a piece is, the longer it takes it to become heated in all parts, and the more gradual must be the heating, in order that an even hardening, or, rather, an even drying, of the mass may take place, so as not to produce a hardened outer rim when the inner substance is yet soft, i. e., contains more H. The H which is becoming rarefied by the increase of heat, has not the power to force itself through the hardened parts; it however possesses a considerable power of expansion, which increases by the constant application of heat; it therefore forms a cavity for itself in which the yet unhard- ened rubber deposits its H as long as it escapes from the rub- ber, and until it is free from it and becomes hard. This is a supposition which becomes more clear by future statements. "Accordingly, in order to prevent porosity, nothing else is necessary than to heat it in such a manner that the heat is equally distributed. This result is attained by observing:— "1. That the heat is equal on all surfaces, and " 2. That the heat be gradually raised and continued, according to the thickness of the plate. "In making plates of considerable thickness, experience taught us to observe the above rules, or the strength would be lessened. " It was mentioned before that steam, like oil or paraffine, serves simply to convey the heat. It furthermore possesses two other properties which make it more valuable than the other substances. 1. Its well known property of conducting heat. 2. Its elasticity. In consequence of its conductability, it dis- tributes the heat evenly; and in consequence of its elasticity, it prevents an uneven* rise of its temperature, while oil, e. g., will follow any change in the temperature that may be caused by the applied heat, Consequently, steam serves as a reservoir of heat, as a balance-wheel serves as a reservoir of power; as the latter distributes the force, so does steam distribute evenly the over-abundance of heat from one point where the flame is larger, or for a moment when the heat is greater it is equalized 580 MECHANICAL DENTISTRY. over the surface and over several minutes of time. Therefore, if the rubber exposed to it is not too thick, so that its influence can reach through the whole mass of the poorly conducting rubber, one may be certain that by the use of steam the heat exerts its influence evenly and the temperature also rises equally. There need be no fear, therefore, that one place will be harder than another, as is often the case with oil; alsn the temperature may be raised higher, and, consequently, less time required for the process, and no fear entertained on account of porosity. "Another property of steam may here be considered which exerts a still greater influence than either its conductibility or elasticity, and which also hastens the process I have illustrated, chemical affinity; viz.: the magnetic—that is, the power of substances to form certain compounds. " The steam acts like a magnet upon the sulphuretted hydro- gen, dissolving this gas with a great deal of alacrity, forming a solution of sulphuretted hydrogen. " It is true that the property of steam is contradictory to the formation of H2S within the rubber. The hardening, in my opinion, is nothing more than dry distillation, and this is nothing more than 'slow burning by the exclusion of air.' This takes place more rapidly the better the provisions are for carrying away the products of combustion, such as carbonic acid, oxide of carbon, etc., and the same is the case in any chemical change. " What the chimney is in the burning of wood, the steam is in vulcanization. In the latter, the product—that is, the H2S —is readily taken up by the steam, thus furnishing the oppor- tunity for more to be formed, and permitting the rubber to harden quickly. This is the main reason why we can vulcan- ize faster when using steam than either oil or sand. " The other properties of steam permit of raising the tem- perature rapidly, and, by absorbing the gas which is formed, serve as a proof of the foregoing assertion, that the hardening of rubber takes place by the escape of one equivalent of H2, and that porosity is caused by hindering the escape of this gas." The time and temperature necessary to produce the requisite VULCANITE BASE. 581 Fig. 393. induration differ with the various compounds in use, and, to some extent, are influenced by the kind of vulcanizing appa- ratus employed, and which present various modifications of form and mechanism, being constructed, in part, with reference to the source and mode of appli- cation of the heat, the former being derived either from coal or charcoal, or other solid combus- tible substances, or from the flame of a spirit-lamp, gas or coal-oil, or some of its products. As solid fuel is no longer employed in vulcanizing, any description of the apparatus specially adapted to this mode of producing heat is Fig. 394. Fig. 395. deemed unnecessary. They have been entirely superseded by others of improved form and construction adapted to the use of either gas, alcohol or coal-oil and its products, for heating 582 MECHANICAL DENTISTRY. purposes. Fig. 393 represents one of Dr. Hayes's Single Flask Iron-clad Ovens, convenient and compact in form, and capable, it is claimed, of vulcanizing in forty minutes at a temperature of 320°, with one ounce of alcohol. Instruments of similar construction are produced by the same manufacturer with a larger boiler capacity for from one to three cases, Figs. 394, 395. The iron-clad improvement in these machines is designed as a protection from the dangers of explosion consequent upon a gradual thinning of the copper boiler from corrosion, a safe- guard of great practical value and concern to those who are continually exposed to the perils of such an accident. The Fig. 396. shell is made of malleable iron, one-eighth of an inch thick, strong enough to resist many times the strain required, and can never be exposed to deterioration. The copper lining is made the same thickness as the copper boilers now in use, and the machine may be used with perfect safety, even when the copper has become as thin as paper; and then, when an open- ing has been fairly eaten through, steam will escape from between it and the iron shell, below the packing joint, giving timely notice that a new lining is required, which can be inserted at moderate expense, and render the vessel good and safe as new. VULCANITE BASE. 583 A peculiar and important feature of these vulcanizers is in placing the thermometer bulb within a mercury bath, outside the steam-chamber, relieving it entirely from the danger of being crushed or checked by the pressure of steam, as is liable to happen when it is exposed to the steam itself, necessitating its frequent replacement. A not less convenient, safe and reliable vulcanizer is that known as Dr. Whitney's, represented in Fig. 396, having a Fig. 397. steam-chamber capacity for from one to three flasks. The boiler is made of wrought copper; the top or cap, which is screwed on, being provided with a thermometer, and an aper- ture filled with fusible metal, which renders explosion of the boiler, unless materially weakened by corrosion, impossible. The author has had one in constant use for many years with- out any perceptible deterioration. A well-approved instrument, called the " Buckeye Vulcan- 199999924 584 MECHANICAL DENTISTRY. izer," invented by Dr. C. H. James, of Cincinnati, Ohio, is ex- hibited in Fig. 397. The mechanism of this instrument is remarkably simple and ingenious, the relation of the different parts being plainly exhibited in the accompanying cuts. The top is very quickly and readily adjusted, and is clamped and held securely in place, making a steam-tight joint, by a single set-screw acting upon the centre of the cover. The application of heat derived from coal-oil and its pro- ducts, for the purpose of vulcanizing, is shown by the accom- FiG. 398. panying cut (Fig. 398), which represents what is advertised as " Hull's Petroleum Gas Burner," and which the inventor claims is " a lamp by which coal-oil and its products can be substi- tuted for gas or alcohol for heating purposes. This apparatus will burn benzine with perfect safety, and with greater heat than either gas or alcohol, and free from smoke. The cut will show its adaptation for vulcanizing, and can be used for any other purpose. There is an attachment for a compound blow- pipe." VULCANITE BASE. 585 Fig. 399 represents the Snowden & Cowman Vulcanizer, an approved apparatus of more recent introduction, resembling somewhat the Hayes's vulcanizer in general construction, differ- ing somewhat in the method of fastening the cover, which, in Fig. 399. the latter, is placed upon the packing joint and secured by a screw collar which screws over the edge of the pot, three set- screws which bear upon the cover, to make the joint steam 586 MECHANICAL DENTISTRY'. tight, while in the Snowden & Cowden apparatus the collar has lugs upon its interior engaging with others upon the pot, thus dispensing with the screw thread. The Edson Vulcanizer, shown in Fig. 400, is provided with a centre screw, by which the flask may be closed within the steam chamber while the steam is rising. It is also adapted to mold- ing celluloid. Fig. 401 represents the Woodward Vulcanizer, in which a steam cylinder and piston form part of the cover, the flasks Fig. 400. being closed by the rising pressure of the steam acting upon the piston. This vulcanizer may also be used in molding celluloid. fe The " New Mode Heater," designed alike for vulcanizing and molding celluloid plates, will be described and illustrated under the head of " Celluloid Base," inasmuch as it is more commonly employed in the latter process, for which purpose it enjoys a deservedly high reputation. VULCANITE BASE. Fig. 402. 587 588 MECHANICAL DENTISTRY. Fig. 402 represents the general body, and Fig. 403, a trans- verse vertical section of Dr. Frederick W. Seabury's Super- heated Steam Vulcanizer and Celluloid Press combined in one apparatus, which, it is claimed, will enable the intelligent den- tist who does not wish to be restricted to the use of one plastic material to accomplish results never before attained. Rubber and celluloid can be manufactured with this apparatus in less than half the time usually required, and a perfect product as- sured every time. Both rubber and celluloid come out of the vulcanizer finished. Cases may be removed from the oven, and others inserted at any time during the process of vulcanization, with a delay not to exceed five minutes, which is a great saving of time, espe- cially with repair work. The apparatus is thus described. " In the accompanying drawing, Fig. 403, Figure 1 illustrates a transverse vertical section of the vulcanizer with dental flasks in position. " In the said drawing, A designates the hollow body of the vulcanizer, which is supported on the legs, a. Within this body is placed the boiler, B, which is formed with the central inverted truncated conical flue, C. The boiler and flue are supported by the tubes d, which are connected at one end to the top of the boiler and at the other end to the chamber d3. " D designates the oven, the lower end or base of which extends somewhat downward into the upper end of the flue C. " The upper end of the oven is formed with lateral flanges d\ which rest upon the top of the case or body A, and thus sup- port the oven in position, and also form the top of the vulcan- izer. " E designates the pressure cover of the oven, which is secured in position by bolts as shown. "e e designate presser-screws, which work through square threaded sockets in the cover and press upon the flask, F, in the oven supported upon the disk m. " El designates two lids, which are pivoted upon the cover in such manner as to be readily removed, and by uncovering apertures in the cover permit visual access to the interior of the oven. VULCANITE BASE. 589 " G designates a valve, which is seated in the flange d1 of the oven, so as to close the channel d?, leading from the pipe d, to the interior of the oven. " H designates a spout, the outer end of it is tightly closed by Fig. 403. the cap h, which leads into the tube I, entering the chamber d3 from above. The purpose of this spout is to convey water to the boiler B. " i designates a pop safety-valve, which is seated on the upper 590 MECHANICAL DENTISTRY. end of the tube I. J designates a steam-gauge connected by the siphon cock j to the chamber d3, into which the tube d opens. " K designates a test-cock communicating with the chamber d3, and b designates a similar cock, communicating with the boiler B on the water level. " In using this vulcanizer a gas or gasoline burner is set be- neath the boiler B, and the valve G is closed ; but the test-cock K is not closed until the escaping steam shows that all of the air is out of the boiler. The heat from the burner will ascend through the flue C and will act directly upon the bottom and sides Of the oven, thus heating the oven and water which has been previously been placed in the boiler, at the same time or separately. "Figure 2 illustrates a vertical section of the solid cover which is used at all times, except when closing the flask, and occupies the same position on the vulcanizer as the pressure- cover E. It is provided with a very sensitive thermometer, immersed in a mercury bath d, which projects into the oven D, and a test-cock v, used to let the air out of the oven before vul- canizing and to blow the steam out through after vulcanizing. " The bar wrench is to be used on the cover bolts only, and must never be used on the presser-screws e e, for which the T wrench is provided. " To Adjust the Vulcanizer for Use.—Open the test-cocks b and k, remove the cap h, pour clean water into the spout H until it escapes through the test-cock b. Replace the cap h, turn it to place with the fingers. If it should leak when the steam is up, tighten it very gently with the T wrench. Close the test-cock b after the excess of water has run out. " Place the gas or gasoline burner so it will heat the oven and boiler at the same time, when you wish to vulcanize. One burner may be used under the boiler, the other in the flue. " For celluloid, place the burner in the centre of the flue, ele- vate it, if necessary, on a box, that as little steam as possible may be generated in the boiler. The pressure of coal gas varies in different places ; a little judgment is necessary to vary these instructions to suit each place. It takes less than thirty VULCANITE BASE. 591 minutes with cold water, and less time, still, with hot water, to get 120 pounds pressure of steam. When steam is up, it re- quires very little heat to keep it. " The water should be renewed every morning the first thing, or some time the pressure will decrease apparently with- out any cause. " Close the test-cock k when steam escapes, and not until then. When the pressure reaches 120 pounds the pop-valve i will blow, at first too freely; a gentle tap on top will seat it. " The valve G is packed with asbestos; a piece is sent with each machine. If the packing leaks, tighten the screw gently. When the screw reaches its seat, turn it back, oil some asbestos, make two or three turns around the stem, and press it in so that the screw will catch. Turn this screw very gently, or you will bulge the barfel. The asbestos will wear one year, to my knowledge, and look as fresh as new. " When operating the machine in vulcanizing, the valve G and the test-cock v should be opened gradually and slowly. By opening the valve G quickly the rushing steam will siphon water from the boiler into the oven. When vulcanizing, there is 115 pounds pressure inside the flask as well as in the oven. By instantly turning the test-cock v wide open, the pressure is removed from the outside of the flask, and the pressure then comes from the inside, which it is least able to withstand. " On the inside of the oven, midway from top to bottom, are four brackets to suspend the disk M. On the bottom side of this disk are two small projections which fit between the brackets under the steam-gauge, and thereby keep the disk stationary. On the upper side of the disk, above the small projections, are two large projections placed so as to receive the square projection on the broad side of nowel; it holds the flask when under pressure directly beneath the three presser-screws. When it is in the right position, the lock-pins of the flask will come directly under the holes EE in the presser-cover, through which the pins are driven home in locking. On the bottom side of this disk, in the centre, is a groove cut to receive the ridge of the flask placed on the bottom to keep warm while molding celluloid or rubber in the other flask. When drying 592 MECHANICAL DENTISTRY. out or heating up the investments, the disk is left out of the oven. When heating up celluloid investments, put the flask in bottom side, or nowel, up, because, there being more plaster in the cope, it requires more heat than the nowel with the metal die. In rubber, rubber and celluloid, and gold and celluloid, put the flask in bottom side down. The flask being in position, Fig. 404. put on the presser-cover, the small curve in the circumference fits the siphon bulb, with the bar wrench tighten the cover bolts by giving each a half-turn in succession until the cover is seated, then with the T wrench turn the presser-screws gently The bar wrench must never be used on the presser-screws The VULCANITE BASE. 593 presser-cover is only used when molding. For drying out, heating up, and vulcanizing, use the solid cover. Place the solid cover in position, first see that the ground joint is per- fectly clean, tighten the bolts by giving each a half-turn suc- cessively ; the bolts must go down evenly or the joint will leak. Smear bar-soap on the ground joint occasionally. "Before putting the flask into the oven to mold, always insert the lock-pins into the holes in the cope, then, when the flask is closed, they can be easily driven down." A heater more recently devised by Dr. Seabury, designated as the " Dry Steam Vulcanizer," in the use of which it is claimed that greater uniformity of color, density and toughness of vulcanized rubber can be obtained than is possible with water-bath vulcanizers, is represented in Fig. 404. It consists of a boiler, with a steam-gauge above, and a plug in the top through which to supply water, connected, by a globe valve, to an oven or vulcanizing chamber, which has a capacity for three flasks. The blow-off cock is in the centre of the cover. The following are the instructions in the use of this heater:— " Fill the boiler only half full of water, measure with a stick; light both burners, thereby the oven will be as hot as the boiler, and, therefore, always dry. Do not put the flasks into the oven until the steam is up to 120 pounds, or the rubber will be melted. After placing the flasks in the oven, turn the cover to place, open the valve wide instantly, by turning the small wheel to the left; keep the valve open while vulcanizing one hour at 120 pounds pressure; at the end of the hour close the valve and blow off steam slowly from the oven, or the plaster will come out of the flasks. " Place the oil lamp under and touching the boiler, by cutting a hole through the board on which the vulcanizer is to be screwed. When the steam is up to 120 pounds, move the lamp so that half the flame will come under the oven; wait ten minutes before placing the flasks in the oven; if the steam condenses, the oven is not hot enough. If the lamp smokes, carbon, which is a non-conductor of heat, will be deposited on the boiler, which must be kept clean. " Globe Valve.—The valve is packed with asbestos ; a piece is 38 594 MECHANICAL DENTISTRY'. sent with each machine. If the packing leaks, tighten the screw gently. When the screw reaches its seat, turn it back, oil some asbestos, make two or three turns around the stem, and press it in so that the screw will catch. Turn this screw very gently, or you will bulge the barrel. ' The asbestos will wear one year, to my knowledge, and look as fresh as new." The accompanying cuts, Figs. 405 and 406, represent Dr. Seabury's improved flask used in connection with his heaters. " It consists in providing the flask with guide-pins inclined to Fig. 405. such an angle that when the upper part of the flask or cope is forced down to imbed the teeth into the gums, it will be moving at such an angle as to allow the projecting alveolar ridge to reach its final position without breaking the plaster investment. "It also consists in the peculiar and novel construction of the guide-pins, by which they can be quickly removed from the flask by a partial rotation of the pin. " Finally, locking-pins are placed at one side of the guide-pins, VULCANITE BASE. 595 so that when the cope of the flask is forced on to the nowel or lower part, the lock-pins may be forced into place and thereby lock the flask. The cover is secured by dove-tail lock-pins and can be easily removed. With this improved flask a stronger, better finished, and more durable plate is produced than is possible with the flasks now in use. " In the accompanying drawing, A is the cope or upper part of the flask. B is the nowel or lower part of the flask. C is the oblique guide-pin inserted into holes formed in the projections D D on the flask. E is the locking-pin inserted into the holes formed in the projections a a at an angle opposite to those formed in the projections D D. Fig. 406. " It is desirable that the top plate should be held in place while being handled, and during the process of vulcanizing for that purpose I form the dove-tail c c, locked by the pins e e. " The cam-pins C are right and left, and are secured in position by rotating them toward the front or narrow end of the flask. The pins should be kept oiled." Figs. 407 and 408 represent Dr. W. .W. Evans' New Vulcan- izer and Celluloid Apparatus combined, which is claimed to possess superior qualities for vulcanizing rubber and molding celluloid and zylonite. 596 MECHANICAL DENTISTRY. Fig. 408 shows a front elevation with top attached and tools needed in the working of this apparatus, which is thus described:— " Fig. 407 illustrates a transverse vertical section with one flask in position. A is a light casing, B the boiler, composed of two separate cups b b, united concentrically by screws b1 to form a water and steam space. The bottom of the boiler A is partly concave, to facilitate ebullition and keep the steam in a state of agitation. D illustrates the oven composed of the inner cups b} having a cover. C is an inlet for steam, d, through the cup b, Fig. 407. Fig. 408. from the boiler, and an exit for steam through the cover d2, both openings being controlled by valves d1 and d3. E E rep- resent the bolts with spherical heads at c, the point of contact with the cover C, which has a corresponding socket to receive it, thus making a steam-tight joint. The top of the head c2 is made to fit the T wrench, that also fits the different valves. To gain more pressure than is usually required, an additional sex- angular portion c1 has been made, whereby any amount of pressure can be exerted. The lower portion of the bolt is VULCANITE BASE. 597 threaded for one-half its distance, and screws into or through the platen F, which is drawn toward the top by turning the bolts to the right, thus closing the flasks G with facility, and without any strain upon the boiler. / is the thermometer, on either side of which are the valves, one connecting the boiler with the oven; the other a conical safety-valve, so arranged that the steam in the boiler can never go higher than the point at which the safety-valve is set. I is a handle to remove the top. Two large flasks may be used at a time, and it is claimed that it will readily stand from 250 to 300 pounds pressure. It is also claimed that rubber vulcanized in this apparatus is much more elastic, denser and tougher, and retains its color better than by other processes, and that it will not shrink from the teeth, and can be vulcanized in thicker masses without becom- ing porous. For celluloid and zylonite, better results, shorter time of molding (one hour and a half) and no lost steam from the boiler, are claimed." Whatever form of water-bath vulcanizing apparatus is used, the flasks are introduced, and sufficient water poured in to cover them. If the flasks are hot when placed in the boiler, water of nearly the same temperature should be added to avoid fracturing the teeth by too sudden cooling. Before screwing on the cap, the rubber packing should be dusted with whiting or pulverized soapstone to prevent adhesion. As it is very important to secure a steam-tight joint, the packing should be uniform, firm, and securely fixed. The webbed rubber is the best for the purpose. In arranging a new packing, cleanse well the groove in the boiler which receives the rim of the cap, and fit the packing accurately. Before screwing on the top, dust the surface of the packing as before recommended, and as the heat rises tighten the screw from time to time until the rubber no longer yields. If the latter precaution is not observed, the packing is either liable to blow out or the joint leak steam. To insure uniform results, it is necessary that there should be absolutely no leakage. When the flasks are properly secured within the steam- chamber, heat is applied and continued until the requisite in- duration of the gum is effected. The time and degrees of heat 598 MECHANICAL DENTISTRY. necessary to effect this result differ somewhat with the rubber compounds and kind of vulcanizer employed. The heat should be raised gradually until the thermometer indicates the proper vulcanizing temperature, when the flame should be lowered, and the heat maintained at this point until vulcanization is com- pleted. In all cases it is best to raise the heat slowly untilit reaches 320°, which temperature should not be attained in less than from one-half to three-quarters of an hour. Where there is any considerable or unusual body of rubber, the time taken to raise the heat to that point should be extended to one hour or longer, for if the mass is heated too rapidly, porosity or sponginess of the thicker portions of the rubber will almost certainly ensue. This result would seem to be due to the en- ergetic evolution of sulphuretted hydrogen gas under a quick heat, the proper elimination of which is checked, and the gas confined within the body of the mass by a too rapid surface induration of the rubber. The evolution of this gas is demon- strated by Prof. Wildman in the following experiment:— " To ascertain if sulphuretted hydrogen is given off during vulcanization, a bulb was blown at the end of a glass tube: this was filled with red rubber ; the tube was then drawn out very small from immediately above the bulb, and curved so that the small part when the bulb was in the paraffine bath could be inserted into a- vessel beside it. " The bulb was then placed in a paraffine bath, and the curved end of the tube inserted in a vessel containing a solution of acetate of lead. The heat was raised to 320° F., and retained at that point for one hour and a quarter. " The mean result of several experiments conducted in this manner was, that during the first thirty or forty minutes after the heat had attained to 320°, bubbles of sulphuretted hydro- gen came over at short intervals, and at the expiration of this time it was evolved in a continuous stream, which continued for a few minutes, causing a copious precipitate of sulphide of lead. After this, until the expiration of the hour and a quar- ter, the gas was only given off sparingly at intervals. This experiment gives us ocular demonstration that this gas is evolved during vulcanization, and in large quantities, and con- VULCANITE BASE. 599 clusively shows that in thick pieces especially the heat should be slowly raised, and the rubber should be under strong pres- sure to insure a successful result." When the American Hard Rubber Company's red rubber is used, the heat should be maintained at 320° for about one hour and ten or twenty minutes. Induration may be effected at a lower heat, but the time must be proportionally extended; or a higher heat being employed, a less time will be required to vulcanize. With the use of the rubber mentioned, the author has obtained good results by vulcanizing for forty-five minutes at 340°. Care should be taken, however, not to over- heat, as the rubber is thereby rendered dark and brittle, and the important property of elasticity impaired. The time and degrees of heat first mentioned, therefore, may be regarded as the safest, and as yielding the best results, though with other rubber compounds, and the use of modified forms of vulcanizers, corresponding differences in time and temperature may be required, and which can only be accurately determined by vulcanizing test-pieces of rubber. In this connection the reader's attention is called to some practical observations on the subject of steam pressure in vul- canizing, and the reliability of thermometers as indicators of heat, and which acquire additional interest if it be true, as alleged, that many of the vulcanizers in use by dentists are insecure by reason of inherent defects of construction, or faultiness in the modes of indicating the elastic force of steam. In commenting on this subject, the late Prof. Wildman ob- serves:*— " As high steam is used in vulcanizing, it is important that the operator should be conversant with the nature of the agent which he employs to accomplish his en*d. It is perfectly safe; but the following will show him that it must be used with discretion and judgment. Numerous experiments have been made by scientific men to ascertain the elastic force of steam at different temperatures. The results of their investigations are not uniform; although they all agree in showing the im- mense force exerted by this agent at high temperatures. Has- * Instructions in Vulcanite, p. 26. 600 MECHANICAL DENTISTRY. well's tables are looked upon as good authority. The results of the investigations of the Franklin Institute Committee, in the higher degrees, give a greater elastic force than the table below quoted. I shall, however, quote the results of the ex- periments of the commission of the French Academy, appointed by the French government to investigate this subject, for the reasons that, from the manner in which they were conducted, they are probably as reliable as any, and that they are extended to a more elevated temperature than the others. Elasticity of steam, raking atmospheric Pressure per square pressure as unity. Temperature F. inch, pounds. 1 212° 14.7 n 233.96° 22.05 2 250.52° 29.4 2i 263.84° 36.75 3 275.18° 44.1 3} 285.08° 51.45 4 293.72° 58.8 4* 300.28° 66.15 5 307.05° 73.5 5h 314.24° 80.85 6 320.36° 88.2 6} 326.26° 95.55 7 331.70° 102.9 n 336.86° 110.85 8 341.78° 117.6 9 350.78° 132.3 10 358.88° 147 21 366.85° 161.7 12 374.00° 176.4 13 380.66° 191.1 14 386.94° 205.8 15 392.86° 220.5 16 398.48° 235.2 17 * 403.82° 249.9 18 408.92° 264.6 19 413.78:' 279.3 20 418.46° 294 " I would here call the attention of those using high steam to an important consideration. In raising steam, the ratio of increase of pressure or elastic force is far greater than that of the increase of temperature. VULCANITE BASE. 601 " By referring to the above table, commencing at 212° and taking steps as near fifty degrees as is given in the ascending scale, we find this exemplified. Thus:— Increase of tempera- Increase of force per Giving a force per ture. square inch. square inch. From 212° to 263.84° = 51.85° 22.05 lbs. 36.75 lbs. " 336.S4 to 314.24° = 50.40° 44.10 lbs. 80.85 lbs. " 314.24 to 366.85° = 52.61° 80.85 lbs. 161.85 lbs. " 366.85 to 418.46° = 51.61° 132.15 lbs. 294 lbs. " This comparison shows clearly how rapidly the pressure increases at high temperatures, and warns the operator that a strong instrument, combined with care and judgment in its treatment, are indispensable to safety. Besides the rapid in- crease of pressure, it must be borne in mind that at high tem- peratures, copper, of which the boiler is composed, becomes weakened, and in a measure loses its power to resist this great imprisoned force. Copper, in passing from 212° to 230° F., loses about one-tenth of its strength, and at 550° it has lost one-fourth of its tenacity." In a paper read before the Massachusetts Dental Associa- tion, January, 1865, Dr. A. Lawrence affirms that " most vul- canizers are now made of sheet copper one-sixteenth of an inch in thickness, and, agreeably to the foregoing facts, have a tensile strength of 1875 pounds; and one four inches in diameter will not sustain a pressure of more than 150 pounds per square inch, or a temperature of 363°. " Let us next ascertain what force of steam is exerted upon the boiler within a short range of temperatures. We find by the tables of Haswell, King and others, that at 320° the pres- sure is 85 pounds; at 324°, 90 pounds; at 328°, 95 pounds; and at 332° it is 100 pounds per square inch. These figures I have verified by a steam-gauge connected with my own vul- canizer, and which I now use in preference to the thermom- eter, as I consider it more convenient, safer, and less liable to accidents. " Practical engineers concur in the opinion that a force of not over one-half the sustaining capacity of the boiler can be safely applied." 602 MECHANICAL DENTISTRY. Intimately connected with the process of vulcanizing is the question of the reliability of thermometers as indicators of heat, or steam pressure. Dr. Lawrence, commenting on this subject, says: " Suppose the bulb of the thermometer gets slightly frac- tured, and, the accident not being discovered, the vulcanizer is put to use, what then ? " If the damage is slight, the mercury may still be made to rise in the tube at high temperatures, but will not truly indi- cate the full heat or force within. Some time ago I had some difficulty in producing a desirable shade in my vulcanite work; it was too dark, as is the case when overheated, and I came to the conclusion that the'gum had deteriorated in quality. Other samples of gum were tried, and at varying lengths of time, yet with the same result. " No defect could be discovered in the thermometer by the naked eye, but a microscope revealed a slight crack in the bulb, and the mystery was solved. But what force of steam was produced during these almost despondent trials ? " Although my vulcanizer would safely bear a pressure of one hundred pounds per square inch, I concluded to use a steam-gauge for the future, and now feel a security in its use positively refreshing." The unreliability of thermometers in connection with vul- canizers has been recognized by many in the profession who have testified to their uncertainty and insecurity as a means of determining with exactness at all times the amount of steam pressure emploj^ed in the process of vulcanizing at a high heat. The steam-gauge (Fig. 409), spoken of by Dr. L., seems very perfectly to fulfill the requirements of the dentist, and may justly claim favorable consideration from the commendation bestowed upon it by the distinguished gentleman who has brought it to the notice of the profession. The following is the author's own account of the instrument: " The gauge most suitable for the purpose in question somewhat resembles a small circular clock, is about six inches in diameter, and marked to register one hundred and forty or one hundred and eighty pounds pressure, with pound dots near the outer circle of the dial. A pointer indicates the force which moves it. VULCANITE BASE. 603 " This size is better than a smaller one, because the spring inside not being crowded to its utmost capacity in vulcanizing, will, of course, retain its working integrity longer; in fact, as long as any dentist now living will be personally interested in the matter. The price of such a gauge, at this time, is $18; and though, unquestionably, more expensive ones can be made, they are no more reliable, the difference consisting in mere 'outward show and adorning.' They can be used with all vulcanizers generating steam, connecting by means of three or four feet, or as much more as may be convenient, of small pipe having a U-shaped bend, or a single coil near and under the gauge to receive the condensed steam, as water alone should enter that instrument. " The following table exhibits a range of pressure sufficient for vulcanizing purposes, with the temperature necessary to produce the same. Pressure Tempera- Pressure Tempera- Pressure Tempera Pressure Tempera- iu lbs. ture. in &>s. ture. in lbs. ture. in lbs. ture. 60 295° 69 305° 78 314° 95 328° 61 296° 70 306° 79 314° 100 332° 62 298° 71 307° 80 315° 105 335° 63 299° 72 308° 81 316° 110 339° 64 300° 73 309° 82 317° 115 342° 65 301° 74 310° 83 318° 120 345° 66 302° 75 311° 84 319° 125 349° 67 303° 76 312° 85 320° 130 352° 68 304° 77 313° 90 324° " It will readity be seen by the above that a pressure of sixty pounds requires a temperature of two hundred and ninety-five degrees by Fahrenheit's scale to produce it, and eighty-five pounds three hundred and twenty degrees, at which latter pres- sure I vulcanize, running one hour, and with the most satisfac- tory results. " The manner of putting up and using the gauge is very simple. All that is required is to secure it, by screws passing through the flange on the back, in some conspicuous and con- venient place, attach a pipe and carry it down ten or twelve inches, give it a bend or curve upward about half its length, or five or six inches, thence at right angles or otherwise, and 604 MECHANICAL DENTISTRY. in any convenient length not less than three feet, to the vul- canizer. " The annexed cut (Fig. 409) is from a photograph of a Whit- ney vulcanizer with the gauge attached, but is by no means the only arrangement which can be made, as, in some cases, con- venience may require more pipe, or a different distribution. "A, table or work-bench; B, vulcanizer; C, side outlet pend- ant cock screwed on in place of the thermometer scale; D, coupling joint; E, angle in the pipe; F, iron pipe, three-six- teenths inside; G, U-shaped curve, five or six inches in depth; H, cock to the gauge; I, gauge. " The fitting, putting up and arranging the entire apparatus Fig. 409. can be done in an hour's time by any gas-fitter, or to those residing away from cities or towns where such mechanics are employed, can be furnished to order by them, or by the parties furnishing the gauge. "All the joints, from the vulcanizer to the gauge, except the coupling, should be ' leaded' with very thick lead paint, and screw together steam tight. " In using the apparatus, the cocks C and H must be turned straight with the pipe, for if shut off at either point, the gauge cannot be acted upon by the steam. I generally heat the water in the vulcanizer nearly or quite to the boiling point, and let VULCANITE BASE. 605 off the heated air by turning, or allowing to remain open, the cock C, then connect at the coupling D, turning the nut tight (not too tight) with a wrench. " So soon as steam begins to form, it is condensed by contact with the cold part of the pipe, and falls into and fills the curve or coil with water, which is then forced into the gauge with a power indicated by the pointer on the dial. The pipe should descend a trifle from the angle E to the commencement of the curve, to facilitate the passage of the condensed steam to that point. "Although vulcanizing one hour at eighty-five pounds affords results satisfactory to me, others may prefer a different time with more or less heat. " The table will be found a guide in such cases. " When the time is up, discontinue the fire, and shut off the steam by turning the cock C. Turn the cock H in the same manner, to prevent a too sudden reverse movement of the ma- chinery of the gauge, the pressure on which should be gradually relieved at any convenient time. " Now disconnect by unscrewing the coupling and dispose of the steam in the vulcanizer by blowing off, or any other means preferred. Further remarks would seem unnecessary to a full understanding of the subject. Having used the gauge almost every day for about six months, I am fully satisfied that it is a decided improvement in vulcanizing, and am so delighted with it that no reasonable sum would induce me to substitute the thermometer." Another appliance, which, in important respects, is an im- provement on the steam-gauge last considered, is exhibited in Fig. 410. " This device was invented by Dr. J. B. Coolidge, of Boston, about the year 1871. A number of them were made and sold at that time, and are to-day in good condition. It is operated by the pressure of steam upon a thin metal disk, which, yield- ing to the pressure, closes a valve which controls the flow of gas to the burner under the vulcanizer. Extensive experiments have been made to procure a metal for the disk which would not lose its elasticity by use, nor give way from the effects of 606 MECHANICAL DENTISTRY. corrosion, and the regulator is offered to the dental profession with the assurance that it will be found to be accurate, service- able, and durable. " The time regulator is of new design. In this, as in the gas regulator, the use of rubber in any form, excepting as connect- ing tubing, has been entirely discarded, as experience has proved that substance to be very prone to deterioration from a variety of causes. It has a metallic valve, which is gas-tight, Fig. 410. whether it be open or closed, and the operating screw being protected from the action of the gas, the valve will be found to operate with ease and certainty. The timing device is believed to be new, and as it is operated by the minute arbor of the clock, instead of the hour arbor, as is usually the case, it is capable of very delicate adjustment as to time, its variation being lim- ited by seconds instead of minutes. " The gas regulator is a better means of maintaining a regu- VULCANITE BASE. 607 lar heat than a thermometer, for the reason that as it acts by the steam pressure its movement is positive, and it can be de- pended upon to act at the desired point after it is once properly set. Before the thermometer can act, it has to receive a certain amount of heat, and the rapidity with which this will be received depends upon the conductivity of the parts between the flame and the thermometer. There are several conditions which will operate to vary and retard the action of the ther- mometer. " The following experiment will illustrate the comparative operation of the two devices: Let the vulcanizer be closed with, say, two inches of water in it, and heat applied. The regulator will turn down the gas, when the thermometer registers some- where in the neighborhood of 300°. If the screw cap of the safety disk is now loosened, and steam allowed to escape for one minute, and the screw cap then tightened, the thermometer will in a few minutes be found to register 320°. " The reason of this is that as air conducts heat very imper- fectly, its mixture with the steam interferes with its conduc- tivity and with the indication of the temperature by the thermometer; but after the air has been allowed to escape, there is an atmosphere of steam above the water in the vulcan- izer, which must be of the pressure due to its temperature throughout its whole extent." When the process of vulcanizing has been conducted a suffi- cient length of time, the flame is turned off and the steam discharged through the safety-valve, if the vulcanizer is pro- vided with one; or the lower half of the boiler may be placed in cold water until the contents are cooled down to about 200°. When time will permit, however, it is better to let the vul- canizer cool gradually. The top is then taken off and the flasks removed. The latter should always be allowed to cool gradually, as the immersion of the flask, while hot, in cold water will endanger the porcelain teeth by a too sudden change of temperature. Neither should the flask be opened while hot, for the plate, being pliable when heated, would be liable to suffer some change of form in forcing the sections of the flask apart, or in removing the piece after separation of the flask. 608 MECHANICAL DENTISTRY. When the plate is removed from the flask, detach carefully all adhering plaster with a pointed knife, and cleanse well by washing with a stiff brush. Finishing.—The rougher and more redundant portions of the indurated material are first removed with coarse files or rasps, following with those of a finer cut (Fig. 411,) or lathe burs (Fig.412), until all parts of the piece accessible to such instruments are reduced to nearly the thickness required. The excess of ma- terial on the lingual side of the plate and other points not admitting of the use of the file, is removed with scrapers of various forms, some of which are shown in Fig. 413. After nearly the desired thickness is thus obtained, and the surface rendered somewhat smooth and uniform, a still further reduc- tion is obtained with the use of sandpaper, using first the coarser and finishing with the finer kinds1. The final polish is then given to the surface, first with the use of finely pulverized pumice-stone, and afterward with either prepared chalk or whiting. The best method of applying the pumice is with flat, circular pieces of cork of various sizes, which may be readily formed by attaching them to the lathe and reducing them to the proper size and shape with a file while revolving. The chalk or whiting may be applied upon a cotton or ordinary brush wheel. In the use of the polishing materials, the latter should be kept constantly and freely saturated with cold water throughout the operation. Partial Dentures Constructed in a Base of Rubber.—The fore- going description of the method of forming entire dentures in a base of indurated gums, together with a knowledge of the manner of constructing parts of sets of teeth mounted on me- tallic plates, will render any extended description of the former process, as it relates to partial pieces, unnecessary. A gutta- percha plate of the required thickness and dimensions is ac- curately molded to a model of the parts, the narrower portions passing into the spaces between the teeth being stiffened by doubling the plate at these points with an additional strip of gutta-percha warmed at the lamp and made to adhere to the primary plate. The central portion of the plate may also be temporarily supported, and its form preserved, by filling in the VULCANITE BASE. 609 Fig. 411. Fig. 413. 39 610 MECHANICAL DENTISTRY. concavity with a layer of stiffened wax. A rim of wax is then attached in the usual manner to those portions of the plate occupying the vacuities on the ridge, when the plate is placed in the mouth and an impression of the points of the opposing teeth secured; it is then removed, re-applied to the model and the heel of the latter extended posteriorly to form an articulat- ing surface for the remaining portion of the antagonizing moclel—the latter being formed in the ordinary way. The teeth are then fitted to the vacuities in precisely the same man- ner as when metallic plates are used, and the wax trimmed to the required fullness. The plate, with the teeth attached, is then placed in the mouth and any necessary corrections made in the arrangement of the teeth; after which it is removed and re-adjusted. In constructing partial sets of vulcanite, it is of the first im- portance, when forming the mold, that the relation of the porcelain teeth to the model of the mouth should be accurately maintained, the reasons for which are fully set forth when treating of the formation of the mold or matrix for full sets. To secure this result with certainty, the following method should be adopted. Having adjusted the plate and teeth upon the model, with the wax trimmed and carved to the required fullness, place the model in the lower section of the flask and fill in with plaster, extending it up to the points of the teeth, binding them to the model, and making the line of separation of the sections of the flask at that point. The ends of the plaster teeth should be cut away sufficiently to allow of a ready separation of the sections. Plaster is then poured in foj the upper section of the mold, and, when hard, the flask is parted and the wax removed from the model and teeth, the latter being retained in the lower instead of the upper section as in full cases. Metallic Clasps attached to Rubber Plates.—Although atmo- spheric pressure or adhesion should be made available in all practicable cases as a means of retaining parts of sets of teeth in the mouth, yet cases occasionally present themselves neces- sitating the employment of clasps. These may be of rubber, but those formed of gold, or gold alloyed with platinum, are more VULCANITE BASE. 611 reliable and better adapted to those cases where the spaces between the teeth are contracted. The following description of the method of constructing them is given by Prof. Wildman :* " First bend the clasp to fit the tooth accurately ; then make the attachment by which it is to be held to the rubber (this may be done by soldering a thin plate of gold or platina to the clasp in such a position that it will be inclosed in the rubber); then perforate the plate with numerous small holes, which should be countersunk on both sides (Fig. 414). This plate entering the base, the rubber filling the holes forms pins which rivet the clasp securely to the rubber plate. " Or the attachment may be made in this manner: On the parts of the clasp that can be covered with rubber, drill one, two or three holes, as the space may admit; insert gold or platina wire, solder with gold solder, then cut off at proper length, and head them (Fig. 415); these act in retaining the clasp in the same manner as the double-headed pins in securing the tooth to the base, and offer the advantage over the per- forated plate of being more easily manipulated, and less liable to become displaced in packing the mold. The clasp is to be attached to the model plate, and will remain secured in the mold when it is opened." A metallic clasp may also be very securely attached to the rubber by drilling a number of holes in that part of the clasp which lies in contact with the rubber, and countersinking them well on the inside of the clasp. Substitution of Plate for Rubber Teeth.—An ordinary plate tooth, such as is commonly used in connection with a metallic plate-base, can be readily rendered suitable for a rubber base. This is done by soldering a narrow strip of gold plate to the * Instructions in Vulcanite, p. 36. Fig. 415. 612 MECHANICAL DENTISTRY'. ends of the platinum pins, forming a loop or staple (Fig. 416), and which, imbedded in the rubber, renders the attachment very secure. A narrow arm of rubber extending to a single tooth may be material^ strengthened by permitting the gold strip, perforated with holes or roughened on its edges, to pass some distance into the rubber, as seen in Fig. 417. Instead of forming a loop or staple as mentioned, it will be preferable in many cases to solder to the tooth a somewhat wider strip than that represented, in the same manner as ordi- narily practiced in backing for gold work, the strip being strengthened by flowing solder at the angle of divergence from the heel of the tooth, and extending thence into the body of the rubber, perforated or roughened on the edges as before recommended. The rubber in this case may be cut away, when finishing, to the angle, leaving nothing but the strip of gold and sub-lining of rubber at the base of the tooth. This method Fig. 416. Fig. 417. may be resorted to with signal advantage in those cases where, on closure of the jaws, the points of the opposing teeth encroach unduly upon the space to be filled, extending nearly to the gum, requiring the tooth of replacement as thinly formed throughout its length as possible. Repairing.—If a tooth or block has been broken, or any change is to be made in the position of either, the teeth or fragments thereof are removed, and an irregularly shaped groove or dove-tail formed in the base occupying the space to be supplied; into this space the tooth or teeth are properly arranged and supported with wax; the dove-tail is then filled in with wax, giving some additional fullness to compensate for waste in finishing. All portions of the piece except the lin- gual face of the plate and teeth are then imbedded in plaster in the lower section of the flask. The upper section of the mold is obtained in the usual way. When separated and all VULCANITE BASE. 613 traces of wax removed, the gum is packed into the cavity around the tooth or teeth. Grooves are then cut extending out from the mold, the two sections heated and forced together, and the process of vulcanizing conducted in the usual manner, the same time and degrees of heat being required as in the first instance. The renewed heat employed renders the surface of the material previously vulcanized somewhat darker, to remove which it is recommended to moisten the surface with dilute nitric acid for a short time, after which the piece is thoroughly washed, and then placed for a few minutes in an alkaline solu- tion to remove any remaining traces of acid. It is also recom- mended to immerse the case in alcohol for five or six hours, and then expose it to the rays of the sun for a like period of time. Dr. A. A. Blount, of Geneva, Switzerland, in May number (1884) of Ohio State Journal, suggests the following method of replacing a broken crown without removing the entire section. Finding it impossible to match the injured block, he says: " I ground the broken tooth down to the gum, as one would for a pivot tooth, and, as I had often done before in mending a continuous-gum piece, selecting a plain rubber tooth the exact size and shape, ground it carefully and accurately to fit, cementing it in place with a plastic cement, which served to hold it firm and prevent the rubber from coining through to the front. The plate being prepared as usual for mending, the piece was vulcanized. After being finished, no one could tell that the block had ever been mended. This method of repairing broken blocks, mounted upon Watt's metal, will be found very practical, as it is somewhat difficult to replace a broken block upon that base." The whole subject of repairing rubber plates is so fully and clearly described by Dr. George B. Snow, in an article entitled " Repairing Vulcanite Plates," that his processes are here given in detail. The author would premise that he has long since abandoned the older methods of " dove-tailing or " undercut- ting," in repairing rubber plates, and would emphasize what is stated by Dr. Snow," that perfect union can be obtained in such cases if the surfaces of contact are freshly cut, absolutely clean, and properly roughened." 614 MECHANICAL DENTISTRY. " It is not unusual to see vulcanite plates which have been cracked or broken, and repaired by what may be termed the ' hole and plaster' system. Holes are drilled through the plate along the edges of the crack, and a new thickness of rubber superimposed upon a mass which, possibly, is already too thick for comfort or convenience, the old crack still remaining as a weak point to occasion further breakage. No advantage was taken of any possibility of union between the old and new material, the dentist having been obviously ignorant of the fact that perfect union can be obtained in such cases if the sur- faces of contact are freshly cut, absolutely clean, and properly roughened. " The great point to be remembered in repairing or making any addition to a vulcanite plate is, that the new and old mate- rial will unite perfectly, and with such firm adhesion that the plate will be practically as good as new, if the surfaces of the old plate where union with the new material is desired are freshly filed, absolutely clean, properly roughened, and of suffi- cient area. To insure these results, wax should not be melted upon the surfaces of union in waxing up, and removal of the wax from the mold should be accomplished by means of in- struments, and not by hot water, unless, possibly, for the removal of very small particles which cannot otherwise be got rid of. Any amount of the old material desired may be cut away, and its place supplied by new; and thus any change wished may be effected. In case of breakage or cracking, the plate should be cut away so that the old defects will be wholly obliterated and new material supplied. " As a first instance, suppose a partial lower plate, supplying the loss of the bicuspids and molars on both sides of the mouth, to be broken through the bar which extends from one side of the mouth to the other behind the incisors. The fracture is generally a clean one, resembling that of glass or porcelain, and the two pieces may be brought into apposition with cer- tainty. The dentist holding the parts together in exactly the right position, the assistant covers the lingual side of the plate at the point of fracture with a few drops of hot shellac from a shellac stick. A little cold water follows, and the two parts of • VULCANITE BASE. 615 the plate are firmly cemented together. A brace is now ex- tended across from the molars on one side to those on the other, by laying a burnt match on the grinding surfaces of the re- spective teeth, and fastening both ends with a few drops of hot wax. By this means sufficient strength is obtained to allow of the plate being safely handled. A piece of paper or sheet wax is cut to fit and reach across the lingual space at the lower edge of the plate, and fastened therein with wax, a coat of shellac varnish is applied to the paper, the surface lathered with soap- suds, and rinsed, and a model run in the same manner as in filling an impression. " After this has hardened, the plate is removed from the model, which is then given a coating of liquid silex. This is always preferably done in repairing plates, at the time when the plate is first removed from the model. The bar may be now wholly cut away, close to the body of the plate on either side, by a jeweler's saw, the cut being made diagonally, so as to make what is termed a ' scarf'joint. The surfaces should be further roughened by making a series of shallow parallel cuts across them with the saw, a thick separating file, or a thin wheel-engine bur. The parts of the plate are placed upon the model, waxed up, and flasked; the model and buccal surfaces of the teeth being covered with plaster, and the parting made so that the plate will be retained upon the model, while the pieces of the bar can be readily removed. After the flask is opened, the pieces are removed, the usual gateways cut, and the packing, vulcanizing and finishing done, as usual. " In the case of an entire lower set broken through the centre, it will be seen that the same directions will apply, excepting as to the amount of rubber to be cut away. A free cut should be made on the lingual side, extending through under the teeth, to and including the labial band; so that the broken surfaces will be entirely obliterated, and at least one-eighth inch in width of new rubber supplied between the cut surfaces. An engine bur will do much of this work nicely, and a wheel bur is very convenient for the purpose of scoring the surface. The making a model, flasking and packing will be done as before. « 616 MECHANICAL DENTISTRY. " If one of the incisor blocks be broken, and needs replace- ment, a new one can be fitted after the model is obtained, and the remaining steps of the process followed as has been described. " Upper plates are sometimes cracked in the centre, the crack extending from under and between the incisor teeth backward over the palate. This often happens from the amount of rubber just behind the incisors being insufficient. It is not unusual to see it cut away at this point, so that the pins are almost or quite exposed, the plate having its usual thickness at a very short distance behind the teeth. A much larger amount of material will be tolerated here than is usually employed, and often with benefit, not only to the strength of the plate but to the articulation of the wearer. The curve of the surface of the plate should be made to resemble that of the palate before the removal of the teeth, and it will be found that the extra thick- ness may extend for half an inch behind the teeth without annoyance to the patient. " A proper curvature to the surface of the plate, just behind the incisors, will do much to prevent the disagreeable whistling in making the s sound, and will assist in giving the correct enunciation to sh, zh, and other Unguals. " If the cracked plate fits a flat mouth, a model can often be drawn from it as it is ; but if the arch is high, and the gums projecting, it is better, after thoroughly cleansing and drying the plate, to finish the cracking by breaking the plate entirely in two. The two halves may now be fastened together by drop- ping shellac upon the lingual side, and a model secured, from which either half of the plate can be easily removed. The whole palatal portion of the plate can then be removed by a saw cut, leaving only a narrow margin on the lingual surface inside the teeth. The remainder of the surfaces of fracture are cut away as directed in case of the lower plate, the new surfaces roughened, the pieces of the old plate replaced upon the model (which has received its coating of liquid silex), waxed up, flasked, packed and vulcanized, the teeth being retained upon the model as before described. The plate, when finished, will show the old rim and a margin of the old rubber inside the teeth. VULCANITE BASE. 617 " It is sometimes desirable to change the substance of the plate entirely, as in case of supposed mercurial poisoning by red rubber; or at least to put what red rubber there may be about the plate entirely out of sight, and to reduce its quantity to a minimum. If this is to be done to the plate last under consideration, it should be prepared for flasking as described, excepting that the labial band should be cut away, and every- thing arranged so that the plate can be separated from the model when flasked. The parts cut away should, of course, be replaced by wax. The case is now set in the flask so as to leave the parting at the upper edges of the gums. The plaster is varnished and oiled, and more plaster built on against the labial sides of the teeth, extending from their cutting edges to the edge of the flask, and again varnished and oiled, so that the appearance will now be precisely similar to a plate flasked so as to be retained upon the model. The ring of the flask is now put in place and filled, and the plaster allowed to harden. " When the flask is separated, the teeth will be found in its , ring section. A few blows of the hammer will dislodge them, with the piece of plaster built against their labial surfaces. This is carefully broken away, in two pieces, if, possible, which are preserved, and the teeth and rubber encasing them are left. The rubber is now filed away as much as is practicable, leaving none of the old rubber in sight, and removing enough from the palatal surface to make a new fit to the model. The teeth and plaster are replaced in the flask, and the case is ready for pack- ing and vulcanizing, and, when finished, none of the old rubber will be seen, and the plate will be practically as good as though the teeth had been removed from the old plate and reset. " It is sometimes difficult to prevent the rubber from showing at the joint between the incisors; great care should be exercised in bringing the sections together properly, and in holding them in position while flasking. If there is room, a small wisp of loose cotton, not larger than a thread, may be tucked into the joint on its palatal side, the edges of the blocks being beveled to admit of this being done. " It is evident that the change from red to black rubber just described ,can be made with a whole plate or a broken one 618 MECHANICAL DENTISTRY. indifferently. If a change of articulation and a new fit to the mouth is also desired, on account of shrinkage of the gums, the plate should be prepared so as to draw from the model, and a few small pieces of wax put in the palatal side to bear upon the alveolar ridge, and give the right articulation by trial in the mouth, the centre of the plate being cut away to facilitate the fitting of the plate to the model. A fresh model of the mouth being secured from an impression, the plate is waxed on to it, the case is flasked with a false piece of plaster built against the labial sides of the teeth, as has been before described, and the plate afterward removed and cut away as much as desired, a considerable amount being always taken from its palatal surface. " This process does all and more than is specified in the Hyatt patent, as it not only gives a new fit, but allows the material of the plate to be substantially changed. Holes and dove-tails, it will be seen, are wholly unnecessary, and the fine serrated edge left by cross-cutting the surfaces of union will be found an excellent guide in scraping the plate to avoid over- laps. The use of shellac as a cement is strongly advised in repairing, as it is rigid and brittle when cold, and the broken parts, if once properly brought together, cannot get out of adjustment without at once attracting attention by the breakage of the cement. Wax does not answer the purpose nearly so well. " The amount of shrinkage in vulcanite, from cooling after vulcanization, is not so generally noticed and provided for as it should be. Plates composed of single teeth do not give trouble from this cause, but full plates, on which sections are mounted, are often very vexatious to the dentist, from the change of shape they undergo from shrinkage. " The reason of this is, that the ends of the sections abutting form an arch of porcelain, which expands or contracts but slightly from changes of temperature. The* rib of vulcanite immediately inside this arch, and in which the pins are em- bedded, forms a second arch, closely attached by the pins to the first one. The plate is molded to the model, and hardened at a temperature of about 320°, and is afterward placed in VULCANITE BASE. 619 the mouth, where the temperature is in the neighborhood of 90°. Under these circumstances the contraction of the rubber which ensues has the effect of lessening the radius of the arch, drawing the heels of the plate together, thus rendering it a little too narrow to fit the mouth accurately. This has the further effect of elevating the palatal portion of the plate, which, when tried in the mouth, will usually be found to rock slightly,—often so much so as to interfere with its fitting. " If the plate has been made upon a model taken from the mouth, the difficulty is overcome by warming the back part of its palatal portion, pressing it down slightly, and cooling it while the pressure is continued; the narrowing of the plate being too small in amount to be of itself objectionable. " This change can be accomplished with more certainty by making a small plaster cast of the palatal portion of the plate, placing upon the part where the change is desired a small piece of folded paper, folded so as to present a thick centre, and forcing the plate down upon it after its palatal portion has been warmed. " The shrinkage here alluded to becomes a more serious mat- ter when the plate is re-vulcanized, in the course of repairing it. It is flasked when the change in form by its shrinkage has already once manifested itself, and again heated to 320°; and in cooling a second shrinkage takes place, it becomes still nar- rower, and its fit, already defective, is made perceptibly worse. It now often becomes a matter of necessity to bring it back to its proper shape before it can be worn with comfort. To pro- vide for this, a small dot should be made with a pointed instru- ment on each side of the plate, immediately behind the molars, and a pair of dividers set to the distance between these points. After vulcanization, the dividers can be applied to the marks, and they will indicate the amount of shrinkage the plate has experienced. Let the plate now be warmed just behind the incisors, and in the mesial line, by repeated short puffs of a blowpipe flame. This must be done carefully, and the heat not allowed to extend over an area much exceeding half an inch in diameter. When the rubber is sufficiently softened, the plate should be taken by the heels, a pull made upon it sufficiently 620 MECHANICAL DENTISTRY". forcible to expand the arch, and a stream of cold water applied. The dividers will at once show if the change made is sufficient. " When the plate is now tried in the mouth, it may be that the back edge will not touch the roof, and air will be admitted under the plate; in which case the back edge should be warmed and forced up to its proper position. " The same remarks apply to full lower plates as well, which often are found to have lost their fit in a measure, after having been re-vulcanized. The process above detailed will suffice to restore them to their former fit, and render them again com- fortable to the wearer." Refitting Gold or Rubber Plates with Rubber Lining.—Gold or rubber plates, whose adaptation to the mouth has become im- paired, in a greater or less degree, by subsequent absorption of the alveolar ridge, may be readily refitted and the adaptation restored by either of the following methods:— First Method.—Take, for example, a full upper set on gold. Secure, in the first place, an accurate impression of the mouth in plaster, and from this a plaster model. Perforate the palatal portion of the plate with from eight to twelve holes at different points, and also the external borders, from heel to heel of the plate, at intervals of from one-eighth to one-half an inch apart, and near the edges. These holes may be enlarged to the di- mensions of a medium-sized knitting needle. On the lingual and buccal surfaces the holes are well countersunk with a bur drill. The plaster model, with the central portion raised to form a chamber, where this is used, and which should be made to correspond, as nearly as possible, in position, form, and thick- ness with the chamber in the plate, is next heated throughout, and when of a temperature that will barely admit of being taken in the hand, remove and cover the face of it with a sheet of rubber, and press it down upon the face of the model with the fingers. Apply the perforated plate to the model, being careful to secure a proper relation of the two; then press the former down firmly upon the model.' To render the vulcanite material still more plastic and compressible, the whole may now be returned to the furnace, and subjected to a uniform heat throughout, when it may be removed, and firm and steady VULCANITE BASE. 621 pressure made upon the plate and teeth, until forced, as nearly as practicable, into contact with the face of the model. Por- tions of gum will be forced through the apertures and out at the borders of the plate; these should be well packed into the countersinks and under the edges of the plate, when the model, with the rubber and plate adherent, may be placed in a vulcan- izing flask and encased bodily in plaster. It is then placed in a heater and vulcanized. If all the steps in the process have been carefully conducted, the fit of the plate will be perfectly restored, with no material change in the antagonism, or none, at least, that is not susceptible of ready correction. The union between the vulcanite lining and the plate will be strong and lasting, and altogether impermeable to the fluids of the mouth. In the case of lower pieces, the holes should be made along the external and internal borders of the plate near the margins In all other respects the manipulations are the same as those described above. It is scarcely necessary to observe that in the use of gold plates, the method is inapplicable whenever it is designed to re-swage the same plate for a permanent piece. In re-fitting rubber plates with rubber lining, it is unneces- sary to provide for the union of the two by drilling holes or other similar expedient. It is only necessary, before packing the rubber lining, to scrape the palatal face of the rubber plate thoroughly, leaving a clean, dry, and roughened surface throughout, when it will be found, on vulcanizing, that the two pieces are inseparably united. Second Method.—Perforate the plate of gold as before directed, and, employing this as a cup or holder, take an impression of the mouth in plaster, pressing the plate up closely to the parts. The plaster forced through the holes, and filling the counter- sinks on the opposite side of the plate, will serve to bind the plaster to the plate, and prevent, with cautious manipulation, the two from separating as they are being detached from the mouth. Before the plaster sets, the patient should be directed to press the teeth together with sufficient force to secure a proper occlusion of the lower with the upper teeth, or the reverse, as the case may be. When removed, the plaster impression lining 622 MECHANICAL DENTISTRY. the plate is trimmed even with the borders of the latter, and then varnished and oiled. The lower section of a vulcanizing flask is now filled with a batter of plaster on a level with its upper surface, and the impression, filled with the same, is turned over and placed in the centre of the flask, with the edges of the plate touching the surface of the plaster. The plate and adhering plaster are now carefully separated from the model. After cutting out the plaster from the holes and countersinks in the plate, the plaster forming the impression is detached from the plate, and the holes and countersinks filled with wax. The plate is then re-adjusted over the model, and (the surrounding surface of the plaster in the flask having been varnished and oiled) plaster is poured in upon the upper surface of the plate and teeth, filling the upper ring. When the plaster is sufficiently hard, the two sections of the flask are separated, and grooves formed, running out from the matrix to the margins of the flask. A sufficient quantity of vulcanizable rubber is now either placed upon the model or packed in upon the palatal surface of the plate—before doing which, however, the wax filling the holes and countersinks in the plate (and which was placed there to prevent portions of plaster last poured, in forming the matrix, from running in and filling them up) should be worked out with a small instrument. The whole being sufficiently heated, the two sections of the flask are forced together, expelling redundant material. The piece is then vulcanized as in the former case. The above method, though somewhat more complicated than the former, is quite simple in its details, and will occupy but little more time, and is, withal, more certain in its results. Manner of Duplicating Sets of Teeth Mounted on Rubber.—When, from accident or other causes, a rubber set becomes broken, or its integrity otherwise impaired, necessitating an entirely new plate with an exact reproduction of the arrangement and artic- ulation of the teeth, the following method, described by the late Professor Wildman, may be pursued with an absolute cer- tainty of success. " Roughen the palatal surface of the rubber to cause the plaster to adhere to it; then use it as an impres- sion-cup to take a plaster impression, being careful when it is VULCANITE BASE. 623 in the mouth to preserve the articulation. In this impression cast the model, trim, cut keys or conical holes at several points in its outer face. Now, before separating the impression from the model, make a cast of the face of the teeth in two or three perpendicular sections, extending to the base of the model, using a solution of soap or other parting substance on the plaster mold. Remove this mold of the face of the teeth, which indicates their true position relative to the model; then take the impression from the model. By the aid of heat suffi- cient to soften the rubber, remove the teeth from it. Next make a model plate with prepared gutta-percha. Now secure the section of the mold of the face of the teeth to the model (their place will be indicated by the keys); adjust the teeth to their proper positions in the plaster mold of them, and build up with gutta-percha or wax to the proper form of the model set. This being done, test its accuracy of contour and articula- tion by placing it in the mouth. Then, using the model, pro- ceed as for making a new set." It will be observed that the above process contemplates the necessity of the patient's presence to secure, in the first instance, an impression of the mouth, and again for a trial of the teeth in the mouth to test the accuracy of arrangement, etc. This procedure is rendered necessary in all cases of faulty adapta- tion of the primary plate, but where the adaptation is satisfac- tory, and it is desired to construct a duplicate set in all respects precisely like the original, the following method, in the main the same as the one just described, may be adopted in the absence of the patient. Oil, or coat with a solution of soap, the palatal surface of the plate to be duplicated; into this pour plaster for the model; trim to the edges of the plate, and give the usual form to the body of the model; form conical holes in the same, and secure sectional molds of the outer faces of the teeth in the manner described by Prof. Wildman. When hard, remove these sections, and detach the model from the plate. Many cases will admit of a ready separation ; in others it will be found impossible to force them apart without frac- turing the model. To avoid such an accident, the model may be cast in sections, the latter being bound together afterward 624 MECHANICAL DENTISTRY'. in their proper relation to each other. But a better plan is to heat the model and plate sufficiently to render the rubber soft and pliant enough to be removed without injury to the model. Cases not admitting of the successful application of either of these expedients must be treated in the manner described by Prof. Wildman, that is, by securing an impression of the mouth. After the separation of the model and plate, the manner of conducting the subsequent steps of the operation is precisely the same as that described in the preceding method. The author has adopted the above process in a number of instances with the most gratifying success in cases of defects or accidents to the original plate, and where the presence of the patient could not be conveniently commanded. CHAPTER XVII. CELLULOID BASE. The employment of celluloid in prosthetic dentistry, though of somewhat recent date, and notwithstanding the very gen- eral failure which attended its first introduction into practice, came rapidly into very general professional favor as a cheap, convenient and serviceable base for artificial dentures. With the more recent improvements in the manufacture and season- ing of blanks, more perfectly adapted appliances for molding, and a more extended acquaintance with the peculiar and dis- tinctive characteristics of this material, it has superseded, in a great measure, all other known plastic vegetable substances for the purpose indicated. That celluloid possesses many important qualities which commend its employment as a base in preference to rubber can hardly be questioned. It is more in harmony with the soft tissues of the mouth, more cohesive in texture, approximates more nearly the natural gum color, contains far less vermilion pigment in its composition, and is less objectionable by reason of the comparative cleanliness accompanying its manipulation. The chief objection urged against celluloid as a base is its low power of transmitting caloric, but it is believed to be less objectionable in this respect than rubber. Both are poor con- ductors, and the soft tissues of the mouth in contact with either suffer, in some degree, as a consequence of this property. Celluloid, as at present produced, and when properly manipu- lated, does not, in any appreciable degree, undergo change of form after molding by warping either in or out of the mouth, as was formerly the case, nor, it is believed, does it absorb the oral secretions. It loses somewhat the freshness and clearness of its original pink color after having been in use for some time, in man}7 cases in a very marked degree. Though not bearing so perfect a resemblance to the com- plexion of the healthy gum tissue as the porcelain imitations, 40 625 626 MECHANICAL DENTISTRY'. yet the near approximation of celluloid to the desired color makes the use of single plain teeth admissible for permanent dentures, and this is unquestionably its crowning merit, and makes it the most desirable of all the so-called " cheap bases." The indiscriminate and almost universal employment of block or sectional gum teeth in connection with rubber has, it may be safely affirmed, done more to degrade the prosthetic department of dental practice than all other causes combined. The optional arrangement of each individual tooth to meet the requirements of special cases in respect to expression, articulation and an- tagonism is one of the absolute and indispensable requirements of a perfect artificial denture. A more general recognition of this important fact must, sooner or later, lead to the entire abandonment of rubber in connection with " leady-made" sectional gum teeth. " Taking into view all its qualities," says a well-known writer, " and leaving out the question of freedom from monopolies, the conclusion is that celluloid has the poten- tialities which should dethrone rubber, and establish itself as the best of the cheap bases." Composition and Manufacture,—The following is the substance of Prof. Charles J. Essig's account of the composition and manufacture of celluloid :— Celluloid is derived from cellulose, a woody fibre, constitut- ing the framework or foundation of plants. Linen, cotton-wool, hemp, etc., are examples of cellulose. For the manufacture of celluloid, the cellulose is first con- verted into paper; hemp is the form of cellulose employed for this purpose, because it has been found to make the strongest paper, and the stronger the paper the better the celluloid. The hemp is first converted into paper in the usual way by paper machines. By this process the form of the material undergoes a physical change only, while chemically it remains the same, viz., nearly pure cellulose, and has a formula of C6H10O5. The cellulose, now in the form of hemp-paper, is converted into pyroxylin by a process technically known as "conversion," this change being effected by immersing the hemp-paper in a strong mixture of nitric and sulphuric acids CELLULOID BASE. 627 for a sufficient length of time, when it is removed from the acids and washed thoroughly. It is now still in the form of paper, but its weight will be found to have increased about seventy per cent., and to have become highly explosive, taking fire at about 300° F. Pyroxylin, then, is the chief ingredient in celluloid, and is reduced to a pulp in a machine similar to that used in paper- making: a thorough mixture is then made of Pyroxylin,.....................100 parts. Camphor,.....................40 " Oxide of Zinc,................... 2 " Vermilion,'.....................0.6 " Some alcohol is used to soften the camphor. The mass is now put under a hydraulic pressure of two thousand pounds to the square inch. The cylinders in which it is pressed have a small orifice in the side near the bottom, and when pressure is » made the celluloid is forced out through this orifice. The immense pressure is to condense or solidify the cellu- loid, and as it is forced out it is cut off in pieces of the proper size, and molded by pressure and heat to the forms in which we receive it. At this point the blanks are still soft, and require to be seasoned; this requires about two months, during which time they are kept in a room at a temperature of 160° F. Processes Preliminary to Molding.—While many of the pro- cesses entering into the construction of artificial dentures, with celluloid as a base, are essentially the same as those required when rubber is used, yet there are, in many important respects, modifications of practice made necessary by the peculiar nature and behavior of the material employed. When the distinctive characteristics of celluloid are well understood, and the operator is familiar with the approved methods of working it, no unusual difficulties attend its suc- cessful manipulation. To attain uniform and satisfactory results, however, it is absolutely necessary that there should be a faithful compliance with every manipulative detail, how- ever seemingly unimportant, which experience in the use of this substance has demonstrated to be essential. Plaster Model.—The inferior plasticity of celluloid, compared 628 MECHANICAL DENTISTRY. with vulcanizable rubber, when exposed to the action of heat, and the consequent greater pressure necessary to mold it into any given form, makes it necessary to give to the plaster model the greatest practicable hardness and strength. To secure these important qualities, it is recommended to use the best quality of coarse builder's plaster, which, though it does not set so quickly as the finer and whiter varieties, becomes much harder and more resistant to pressure when thoroughly dried. In- creased hardness will be secured by adding to the plaster mix- ture a small quantity of clean white river or lake sand or marble dust. A smoother face will be given to the model by first coating the surface of the impression with a moderately thin mixture of fine plaster, and, as this begins to set, fill in with the coarser variety* for the body of the model. The plaster for the model should be mixed as thick as can be well poured, taking care, as it is slowly introduced, to expel any confined air by tapping or shaking the impression-tray as the plaster flows in. In cases where there is any considerable anterior projection of the alveolar ridge in front, above or below, the correspond- ing portion of the plaster model is liable to be crushed under the pressure necessary to mold celluloid. To prevent such accident, it has been recommended, in addition to the expe- dient to be mentioned hereafter, to place in the front part of the impression a curved piece of brass plate punched full of holes, one-half or three-fourths of an inch wide, which, when the impression is filled, will be imbedded in the central portion of the plaster ridge, and extend some distance into the body of the model. In extreme cases, where the ridge is very thin and the pro- jection spoken of excessive, it may be necessary to substitute metal for plaster in forming the model. In this case the latter may be obtained by pouring block-tin or Babbitt metal directly into the plaster impression, which should first be thoroughly dried, and the cavity for the air-chamber formed before pouring. A solid metal cast, however, should never be employed when there is any considerable undercutting, as is often the case on CELLULOID BASE. 629 either side of the median line in front, forming the canine fossa, and posteriorly underneath the maxillary tuberosities) since, in such cases, it will be impossible to detach the metal cast from the case when molded. The separation can be readily effected by substituting a metal shell for the solid cast. The shell is formed in the following manner: Secure a perfect mold of the plaster model in sand, and fill into this with fused block tin of the purest kind, pouring it as hot as can be poured without producing bubbling of the metal. As the metal cools first at the surface, a shell will form externally in a few sec- onds, when the box containing the mold should be inverted and the central fluid mass poured quickly out at the back part of the mold in order to secure the thinnest portion of the shell in front, where it should not be thicker than ordinary card paper. A little practice, with a few failures at first, will enable the operator to secure the desired thickness of the shell with tolerable exactness. When obtained, the shell is filled in with hard-setting plaster to form the metal-faced model to be used in molding the celluloid. When the case is finished and the plaster removed from the shell, the overlapping borders of the latter may be readily drawn in toward the centre with pliers, and the shell disengaged from the undercut spaces. To facilitate its removal, the shell, before filling in with plaster, may be divided vertically at intervals with a fine saw, extend- ing the cuts from the margins to near the summit of the ridge. Waxing or Modeling.—After having arranged the teeth for any given case, place them with the trial plate on the model, and build out with wax, paraffine and wax, or modeling compound. In carving or modeling these materials, much time and labor may be saved in final finishing of the piece, and a more com- pact surface given to the celluloid, by securing in the first place the exact form and fullness required in the completed set. When this is done with instruments, especially adapted to the purpose, the general forms of which are represented in Fig. 418, additional smoothness of the surface may be obtained with a blowpipe flame applied in such a way as to produce simple surface fusion of the wax or other material. The palatal and MECHANICAL DENTISTRY. Fig. 418. Fig. 419. exterior surfaces may then be covered with No. 60 tin foil, carefully bur- nished into close contact. A closer imitation of the granular appearance of the natural gum exteriorly may be obtained by pitting or " stippling " the surface with a small pointed in- strument, care being taken not to perforate, but simply indent, the foil, or a flat-faced serrated plugger may be used for the same purpose. Investing.—The piece prepared as above is then placed in a flask espe- cially designed for celluloid, (see Fig. 419,) invested in plaster, and the mold or matrix formed in the same manner as practiced when rubber is used. In case the ridge overhangs, or is under- cut, the model, before being encased in the lower section of the flask, should be cut across diagonally, with the slope toward the heel of the model, thus depressing the latter pos- teriorly, as exhibited in Fig. 419. By this means the projecting portion of the ridge will be brought more directly in a line with the pressure in closing the flask. It is quite as important that the CELLULOID BASE. 631 encasing plaster forming the matrix should be as hard and re- sistant to pressure as that entering into the composition of the plaster model. If this condition is not secured, there will be great danger, not only of fracture of the model for the want of adequate lateral support, but of displacement of the teeth by being forced into the plaster. So important is the right condition and manipulation of plaster in the use of celluloid, that the author feels warranted in adding, to what has already been said in this connection, the following judicious comments contained in a pamphlet issued by the manufacturers of celluloid:— "Plaster should always be mixed as thickas possible, and, if convenient, allowed to set over night, with the flask open, and dried in a warm place, as it is thereby rendered much harder. Simple as the operation is, comparatively few understand how to mix plaster so as to get the greatest strength and resistance to pressure. The proper way to mix plaster for both models and filling flasks is as follows: First, stir up some plaster as thick as can be well poured, taking care that there is no excess of water; pour some of this into the flask or impression to be filled, and shake down well. Then, into what remains in the bowl, stir more plaster until you have a mass so thick that it can be piled up. With this the flask is filled up and thoroughly shaken down. It is surprising how much plaster can be stirred in after the first is poured out, and also how thick a mass, such as described, will settle down in the flask without bubbles. The thinner plaster first poured in will run and be driven by the thicker afterward added, into all the crevices, and most of it will escape from the flask, leaving a body of solid, resisting plaster that cannot be obtained by the ordinary method of mixing." In flasking the case, the line of separation between the upper and lower sections should be along the borders of the plate. This is particularly necessary when the gum is "stippled." When the piece is incased, and the plaster has sufficiently hardened, the two sections of the flask should be carefully separated, and this can be done with greater safety to the model and other portions of the matrix, and with less liability 632 MECHANICAL DENTISTRY. of loosening and detaching the teeth from the plaster, by first applying just sufficient heat to the flask to soften the wax and trial plate, being careful not to melt the wax by too great or long-continued heat. When the flask is separated, all portions of wax or other material should be carefully and thoroughly removed from the mold, and if any remain, not accessible to instruments, the section or sections of the flask containing remains of wax should be placed in a clean vessel under clean water and well boiled until all is expelled. The thin, frail edges encircling the matrix in both sections of the flask should then be cut away somewhat, and well rounded to prevent fracture and consequent mixing of particles of plaster with the celluloid in molding. When this is done, put the flask together and see if there is ample room for the " nose " of the model to pass the edge of the matrix. To permit the escape of surplus material in molding, either of the following plans may be adopted: 1. Cut two concen- tric grooves in the plaster of the upper or lower section com- pletely encircling the matrix, the inner one not less than one- fourth or one-sixth of an inch from the margin of the mold, and the other at the border of the flask, the inner side of the latter forming a part of the outer groove. 2. Bevel the plaster around the mold, commencing about one-fourth of an inch from the margins of the latter and extending it to the sides of the flask. 3. Cut cone-shaped cross or radiating grooves from the inner circular gutter to the margins of the flask,—shallow where they connect with the circular groove, and deepening and widening toward the edges of the flask. In no case should cross grooves be made communicating with the matrix, as these afford too ready an exit for surplus material, and prevent that " back pressure" so essential to a complete and compact filling of the mold. The grooves should be deep and ample enough to receive all surplus, otherwise it will be difficult, if not impossible, to close the flask perfectly. In the use of gum teeth, holes may be drilled in the matrix inside the teeth, opposite each joint, not over an eighth of an inch in diameter, and as deep as it may be deemed CELLULOID BASE. 633 necessary. These act as waste gates, and relieve the blocks from pressure. Selection and Preparation of the Celluloid Plate or Blank.—The mold having been prepared in the manner described, a suitable blank should be selected, and, as it is important that this should be, as nearly as possible, the size and general form of the mold, a good assortment of plates, for both entire and partial pieces, should be at command from which to select for any given case. Special attention is directed to this important requirement. Celluloid does not, like rubber, flow together and intimately intermix when exposed to heat and pressure. If, therefore, the blank is, in any considerable degree, wider than the model, or its central or palatal portion fuller and deeper than that of the model, the material, when under pres- sure, will lap or fold upon itself along the lateral walls of the arch, and, failing to unite, will form grooves or fissures. On the other hand, if it is not wide or deep enough, the material is liable to be stretched and torn. The blank should be just large enough to fill all parts of the mold perfectly, with some slight excess, and the central portion should always be some- what thicker than the corresponding part of the trial or pattern plate. As celluloid cannot be depended on to flow from one part of the mold to another, it is important that there should not only be an excess of material, but that this excess should be, as nearly as practicable, distributed throughout all portions of the matrix. A neglect of this precaution will result either in an imperfect filling of the mold in some places, and consequent defect of the plate, or a porous condition of the celluloid will be found wherever the material, though apparently filling the mold, has not been impacted with sufficient force. The selected blank should be conformed as nearly as pos- sible to the shape of the mold by heating it in boiling water and pressing it with the fingers into the section of the matrix containing the teeth; after which the necessary fullness of the several parts of the blank may be obtained by dressing away redundant portions with files, a small bracket saw, or the knife, first softening the plate in boiling water before using the latter. 634 MECHANICAL DENTISTRY. Greater exactness in the required amount of celluloid neces- sary in any given case may be obtained by measurement, the simplest method being by the use of the Starr instrument, illustrated in the chapter on Vulcanite. It must be remembered, however, that this device only determines the aggregate amount of material necessary, and that, while it may be a safe guide in the use of rubber which flows freely, it may lead to failure when celluloid is employed, unless care is taken that all parts of the blank correspond with the capacity of the mold. A more reliable, though somewhat tedious, method of secur- ing exactness in the quantity and distribution of material nec- essary, and which acquires special value in cases where there is unusual danger of fracture of the model or teeth, and espe- cially of the latter when gum teeth are used and these are ground very thin, is the following, given by a correspondent of the Dental Cosmos: "After preparing the case ready to flask, remove the teeth from the pattern; stop the pin-holes, then remove the pattern and carefully flask it. When the mold is ready, remove all the wax or material of the pattern; place the celluloid ' blank ;' apply heat, and cast the same as if for final case. Remove the flask from the heater; place it in the clamp and cool rapidly. When it is entirely cool, remove it from the flask, and trim as carefully as for final case until the blank is almost the same as the pattern in thickness (it always comes out thicker). Now you have a blank with but little excess; only what the vacuum and pins displace, or slightly more, and exactly the shape of the pattern, minus the teeth. Now set up the case again, being careful to make the pattern the same size; flask, and when ready remove the pattern; if doubtful as to amount of excess, pare the edges of the mold slightly, which will be all that is needed. Replace the blank ; apply heat, when but moderate pressure will be found neces- sary to bring the flask entirely together. If dry heat is pre- ferred, dip the edges of the blank to come in contact with the pins in spirit of camphor for a few minutes before casting." Before the blank is placed in the flask preparatory to mold- ing, some provision should be made against adhesion of the plaster to the plate. This may be done by oiling the surface CELLULOID BASE. 635 of the model, or by coating it and other portions of the matrix with either collodion or liquid silex, or by rubbing the surfaces well with French chalk, or powdered soapstone ; or a layer of tin foil may be interposed between the model and blank. The following novel method of coating the surface of the model with tin is recommended by Charles P. Alker, of Bordeaux, France: " Reduce ordinary collodion with about three times its bulk of ether, and add powdered tin until the solution is well impregnated with the metal. The tin is the same that is sometimes used for coating plaster images. When properly mixed and applied with a brush, an even covering of tin is formed upon the model, so dense as to closely resemble tin foil, and so firm as to not be detached by boiling water or heat. The plate is readily cleansed with a coarse brush, and presents the appearance of having been made in a metallic mold." More perfect results, however, it is believed, can be obtained in the use of a metal-faced model in connection with the use of tin foil, as before described. A piece thus encased in metal will require no more final finishing than is necessary to remove surplus material and dress and polish edges. The case, as thus described, is now ready for molding. Molding.—The various machines or heaters now generally employed in molding celluloid into dental plates contemplate the use of either glycerine or oil, steam or dry heat, for the pur- pose of producing the requisite plasticity of the material sub- jected to pressure. There is considerable diversity in the form and construction of heaters designed to utilize these several mediums for the conduction of heat, as well as differences in the modes of applying pressure, and while each has, doubtless, some special points of merit not possessed by others, satisfactory results may, with careful and intelligent manipulation, be at- tained by the use of any one of the many recommended. The limits of this work will only permit the introduction of such as are believed to be in most general use. Hat Moist Air (so-called "Dry Heat") Machines.—In the use of these heaters, the water with which the plaster is impreg- nated is relied upon to produce the steam necessary to carry off all excess of camphor from the celluloid in the process of 636 MECHANICAL DENTISTRY. molding. An essential point by this method is to have the plaster in the flask thoroughly wet, and this may be better at- tained by setting the flask in a vessel of water before placing it in the heater. To provide against insufficiency of moisture in the plaster, a small quantity of water may be introduced into the tank before applying heat. Fig. 420 represents a molding or packing machine of the class here spoken of, and is designated as the " Best." * The inside chamber is of cast-iron, surrounded by a sheet-iron Fig. 420. casing. The lid, of cast-iron, forming a part of the clamp, is pierced for the passage of three wrought-iron screw-bolts,'— the nuts being on the upper side and easy of access. When * Other machines, applicable to the so-called "dry-heat" process are "Brown's" and "Hayes's" celluloid apparatus, provided with screw-bolts similar to the "Best," the Hayes heater being used in connection with the Hayes or Whitney boiler; the " Hindsman Heater;" a "Celluloid Press" mauufactured by Spencer and Crocker, of Cincinnati, aud, doubtless, others with which the author is unacquainted. All of these, except the " Hindsman " Heater, are adapted to either dry heat or glycerine. CELLULOID BASE. 637 these nuts are turned for the purpose of closing the clamp, the bottom portion of the clamp is drawn up by each revolution away from the flame, thus avoiding the danger of overheating the plate, and securing a uniform heat. The bottom of the cast-iron chamber and the lid are pierced with holes, to allow a circulation through the chamber, for the purpose of carrying off the camphor which is disengaged in the process. With the celluloid blank adjusted to its proper position in the flask, the latter is placed in the clamp and the top screwed down until it slightly presses the flask. It is then placed in the oven or tank, and heat applied. If gas is used, the form of burner shown underneath the heater in Fig. 420, which gives a pure blue flame without smoke, may be used. If gas cannot be commanded, however, any of the alcohol or kerosene lamps commonly employed in vulcanizing may be substituted; or the " Hot Blast Oil Stove," especially adapted to the " Best" machine, and exhibited in connection with the latter in Fig. 421, and its construction in detail shown in sectional diagram, Fig. 422, will be found con- venient and efficient. Having applied the heat, it is of the first importance that unremitting attention should be given to the process of mold- ing until it is completed. If pressure is applied before the celluloid is rendered somewhat plastic, or too great force is ex- erted during the earlier stages of the process, and without suf- ficient intervals of rest, there is danger of crushing or fracturing the model, and of impairing the articulation by displacement of the teeth. On the other hand, the nature of celluloid is such that if it is exposed to a temperature of 270°, without being under pressure, the camphor evaporates, and the mate- rial, besides being rendered hard and intractable, is puffed up, exactly as a loaf of bread is raised by yeast, and filled with air cells, and thus rendered porous. Celluloid begins to soften at about 225°, and will then yield slightly to pressure, but this should be applied very gently at first, with no more force than can be readily exerted with the thumb and finger. As the heat increases, and the celluloid becomes more and more plastic and yielding, the pressure 638 MECHANICAL DENTISTRY. should be correspondingly increased, but always interruptedly, giving the material time, between each turn of the screw or nuts, to escape from under the pressure. No considerable amount of pressure will be required in any case until near the close of the operation, when the mold is completely impacted, and the excess is being forced into the grooves or gateways as the flask comes together. At this point considerable force will be necessary to close the flask perfectly, and somewhat longer intervals of time should occur between each turn of the screw or nuts. Fig. 421. Fig. 422. ■fill A. Eeservoir, made of galvanized iron. B. Top of reservoir. C. Chim- neys. D. Drum. E. Hanging partition, which keeps the radiated heat from res- ^Jjfc ervoir. F. Principal air deflectors. H. | Supplementary air deflectors. T. Tank lllljjjl surrounding wick tube. R. Perforated l™Ka^^^^lii:^M|R: ■- 1IPP"~~ rinS tnr°«gh which all the air that sup- ^Sjfc Jfg^- plies the stove passes. W. Wick cham- ber. X. Wick tubes. During the progress of the molding, the flask should be withdrawn occasionally for inspection. If, in the case of cen- tral pressure, the flask is found to be closing unevenly, it should be loosened in the clamp and readjusted in such manner as to correct the faulty approximation. No difficulty will be experi- enced in this respect in the use of clamps provided with screw- bolts, as pressure may be applied at any point, and the flask be made to close uniformly without the necessity of shifting the latter. 763757�754 376757273633���37301 CELLULOID BASE. 639 The moment the flask is completely closed, the heat should be turned off, and the piece allowed to cool gradually. In no instance should the flask be removed from the clamp (unless securely locked, as is practicable with the " standard " flask),* until it is stone cold. In cases where the material is of extra thickness, or where the shape of the blank is totally altered, longer seasoning is advisable, and the flask should be placed near a stove or over a register (keeping it closed by a clamp, or by an instrument or piece of iron put through the holes in the standard) for half a day or more, at a temperature not over 140°. If these directions are observed, no trouble from warping plates will be experienced. Molding in Glycerine.—Glycerine, as a medium of imparting heat in the process of molding celluloid, has almost entirely superseded the use of oil, paraffine, and other allied substances originally employed. It is a favorite method with many prac- titioners, and is recommended by the manufacturers of celluloid as superior to any other. The long and familiar acquaintance of these parties with the composition, nature, behavior and treatment of the material they produce entitles their opinions and preferences to more than ordinary consideration. The improved glycerine apparatus manufactured by them is exhibited in Fig. 423; consisting of a tank, A, for containing the glycerine; a stand, S, with detachable legs, L, which slip into slots, as shown at S; an alcohol cup, shown at K in sectional diagram of steam machine, Fig. 425; a screw clamp, B; a flask, C ; and a thermometer, D, to indicate the heat. Either alcohol or gas may be used with this machine. When kerosene is employed, the manufacturers recommend the use of the " leader" oil stove, which will be seen attached to the "steam" apparatus, Fig. 424. When this stove is used, the long legs of the steam machine must be substituted for the shorter ones represented in Fig. 423. Having placed the blank in the flask, put the latter into the screw clamp and turn down the screw until it touches the flask lightly; set the whole into the tank and pour enough glycerine into the latter to come up to about the top of the flask. Apply * Manufactured by the CVlluloid Company, and represented in Fig. 423. 640 MECHANICAL DENTISTRY. heat, and proceed with the molding in the same manner as described in connection with the " moist air " method. The heat should not be permitted to rise much above 280°. If the flask is not closed when that heat is reached, reduce the flame, and do not hasten the closing. A little practice will enable the operator to graduate the pressure exactly, without reference to the thermometer. Molding in Steam.—The best adapted apparatus where steam is used in molding is that manufactured by the Celluloid Com- pany. A sectional diagram of the same is shown in Fig. 425. It consists of the following parts: The base, or standard, J (now made with detachable legs, as in cut of glycerine machine); the boiler, B; the cover, D, to which is attached the safety valve, H; the plunger, E, and alcohol cup, K; the screw, F, for closing the flask, operated by the handle, L; the gland or packing ring, G, the object of which is simply to prevent the steam from leaking around the screw; and the wrench or spanner, S. The stand is the same as that for the glycerine machine shown in Fig. 423, and is furnished with short legs, as shown CELLULOID BASE. 641 m that cut (for alcohol or gas), or long legs as above, as desired. To use the old steam machine with the " Leader " stove, it is necessary to order only the improved stand with long legs. The company send always the short legs unless otherwise ordered. The following are the directions given:— " In using the steam machine, care should be taken to keep Fig. 424. M and N, in the sectional drawing, represent steam packing, to make the boiler tight/ it in good order. The screw should be well oiled with only the best sperm oil, which will not gum, and kept so that it can be easily turned with the thumb and finger. If the machine, when received from the depot, works hard, the screw should be run out, the gland unscrewed, and the rubber packing 41 642 MECHANICAL DENTISTRY. loosened up, so that it will not bind the screw. Do not turn it down tight again until you heat it up, when, if it begins to leak, it can easily be tightened. Bear in mind that turning this gland merely prevents the escape of steam, and does not affect the pressure on the flask. " The safety-valve should be kept free from gum, and if either it or the screw is fouled, it should be well cleansed with kero- sene. This valve, in the machine now sold, is so constructed that it blows off at about 275°, a temperature that celluloid will bear very well; and as the heat, so long as water remains in the boiler, cannot, if the safety-valve is kept in order, be raised above that point, it is impossible to burn a plate in this machine. While this is true, it is also true that too long an exposure to even 275° in steam tends to injure the quality of the celluloid, and for this reason the heat should be continued no longer than necessary, but should be at once reduced by blowing off steam as soon as the molding is completed. The first machines were constructed with the safety-valve much heavier, and all in one piece, and were adjusted to a tempera- ture of nearly 300°, which was higher than necessaiy or ad- visable. It is recommended, therefore, that those having that style of valve should cut off about one-fourth in weight from the lead weight, which can be easily done by removing a little wire which passes through the stem and weight. A modern valve will be furnished when ordered. When molding, fill the boiler partly full of water. The amount is not material, but there should always be enough to cover the ribs at the bottom. Have the screw well turned back, until the plunger, when placed in position, will rest against the top of the boiler, otherwise the flask may be pressed upon while screwing down the cover, and the cast injured. Turn down the cover snugly; see that the gland is turned back, and the screw works freely. Many failures have occurred by neglecting this simple matter. If it works hard, it is impossible to tell how much or how little pressure is being exerted; there may be too much, and blocks or cast be broken; or too little, and the plate made porous. In all methods of working celluloid, the sense of feeling is the -best guide as to when and how hard to turn; but in order to CELLULOID BASE. 643 have this there must be perfect freedom of motion of the parts. The time elapsing before turning is not reliable, as it varies with the heat employed, the temperature at starting, the amount of water in the boiler, the draughts of air to which the flame may be subjected, etc. " After placing the flask in position, turn down the screw very gently, with thumb and finger, until you feel it touch the flask. Fill the cup with alcohol and light it, or light the gas. The safety-valve is made in two parts. The upper portion may be suspended by the pins in the lead weight; the valve will now blow off steam (if in proper order) at a temperature of 225°. Until this occurs, no particular attention is necessary, but from that time the exclusive attention of the operator should be given to the molding. Many failures occur from the want of this, for the plate may be easily injured from too much heat without proper pressure. But fifteen or twenty minutes, at the most, will be required from this point, with proper heat, and nothing else should be attended to. " At the point when the steam escapes from the valve with the upper portion suspended, the plate will soften, and the screw will be felt to yield to light pressure with thumb and finger. The upper weight should now be dropped down. Turn the screw very carefully, stopping when you feel the resistance in- crease ; as soon as it yields again, turn it more, going slowly and carefully at first, but increasing the pressure somewhat as the steam gets up, which you will know by occasionally raising the valve. It is just here that judgment is required to avoid, on the one hand, too much pressure before the material is suffi- ciently softened, which would result in fracture of the cast or blocks, disarranging the articulation, or a ' flaky ' plate ; and, on the other, too little pressure after the heat is up, which would result in injuring the quality of the material. The pressure should be followed up as the heat rises and the screw yields, the object being to get the whole of the plate under pressure, in • every part of the mold, by the time the steam blows off quite sharply and steadily on raising the safety-valve. After this the pressure should be increased, but time should always be given between the turns for the slowly flowing cellu- 644 MECHANICAL DENTISTRY. loid to escape from under the pressure. Toward the close of the process, the pressure should be considerable; in fact, about all that can be applied with the machine, and should be con- tinued as long as the screw can be turned. If the operation Fig. 42c. has been properly timed, the steam will blow off at the safety- valve at about the time the molding is completed, and the alcohol in the cup is consumed. If it should blow off before 6116 CELLULOID BASE. 645 that, no harm would be done, as the heat cannot become too great if the safety-valve is kept in proper condition. These remarks apply to the use of alcohol in the cup furnished with the machine. If any other heat is used, the flame should be sufficient to complete the process within thirty to forty minutes. If more than this time is consumed in the molding, the quality of the plate is injured. " Do not allow the water to be all converted into steam, as the steam would then become superheated, and a dangerous condi- tion ensue or the plate be ruined, while the safety-valve would not indicate it. Always have plenty of water in the boiler, and if steam should cease to issue on raising the valve, the heat should be at once withdrawn." It has been demonstrated by experimental tests, and is now very generally conceded, that the best results are obtained in the use of celluloid by subjecting it to dry heat in the process of molding, the material, when exposed to a high temperature under such a condition, retaining most perfectly its form, color and consistence. Hence the celluloid presses of more recent introduction, while they are also equally well adapted to vul- canizing by the same means, are provided with a distinct chamber in which hot air, of a higher temperature than can be safely employed with glycerine or steam, is utilized to secure the greatest practicable plasticity of the celluloid. Approved appliances of this kind are those devised by Drs. Seabury, Evans, and Campbell. The former two have already been described in the previous chapter. Dr. Campbell's apparatus, familiarly known as the " New Mode Heater," exhibited in Fig. 425, is constructed as follows : The apparatus, designed alike for vul- canizing and molding celluloid, used more generally, perhaps, for the latter purpose, consists of a cylindrical cast vessel, having two chambers, one within the other, the inner one being sup- ported by piers or columns connecting its sides, top, and bottom with those of the outer chamber, the whole being made in one casting. The outer compartment is the steam chamber or boiler, and incloses the hot-air or packing chamber on all sides, except the front, where the walls of the two chambers converge and become one, for the purpose of permitting access to the 646 MECHANICAL DENTISTRY. packing chamber. A door made of the same metal as the boiler, and fitted with lead packing, to make it steam tight, is held in place by a bridge secured with screws. The door is also provided with a plate-glass light (shown in cut), through which the operator can watch the progress of the molding in the oven. The only communication between the two chambers is by means of a valve having its seat in the top of the pack- ing chamber, and controlled by a hollow stem which passes through the top of the machine. B is a mercury bath; C, thermometer; D, screw plug; E, lam nut; F, stem of steam valve; G, screw cap; H, large screw for closing the flask , I, I, I, smaller screws for same purpose; K, K, K, L, nickel-plated caps for screws; O, O, steam chamber. The packing chamber is heated by steam generated in the outer compartment, which is kept filled with water on a level with the top of the oven. The water is introduced through an opening in the top and side of the boiler, into which the ther- mometer is screwed, and which may be removed for the pur- pose. Steam may be introduced from the boiler into the packing chamber by partly unscrewing the lam nut, E, or wholly ex- cluded by tightening the same. With this arrangement, an absolutely dry packing oven is possible in molding. The fol- lowing directions in the use of this heater are given by the inventor:— " To secure the best practical results, celluloid should be molded or pressed into the form desired at the highest possible temper- ature which will not burn it. To prove this, it is only necessary to mold a plate on a metal cast at the lowest temperature at which it can be done, which is less than 212°, and another on the same cast at the highest temperature possible, say 310° or 320°, and lay the two aside for a few days, when it will be found that the one molded at the lower temperature will not fit the cast, while that molded at the higher temperature will fit as well as when first made. The reason is that the low tempera- ture fails to overcome the tendency of the plate to return to its original form, while the high temperature renders it so thor- oughly plastic that this tendency is entirely eradicated. This is proportionally the case with pieces made at intermediate CELLULOID BASE. 647 temperatures; the higher the temperature to which the plate is subjected in molding, the more exactly will it hold its new form and the less will be its tendency to warp. " Celluloid may be readily and safely manipulated in the New Mode Heater at 320°, a temperature many degrees higher than is deemed safe in other machines, and which accomplishes perfectly the result above noted, and produces a plate which is believed to be absolutely unchangeable in color, form and texture. When this very high temperature is employed, the celluloid should be in the machine only long enough to permit the closing of the flask; for the reason that heat vaporizes the camphor—the solvent of the material. If too much of this is driven off before the flask is closed, it will be almost impossible to mold the blank to the desired form. The sooner the flask is closed after being placed in the oven, the more readily will it be done, and the better will be the result. " The molded surface of a piece of celluloid is much more durable than its interior, and will retain the color better. It is obvious, therefore, that this surface is essential to the integrity of the plate, and should be preserved intact. To insure this, the case should be so prepared that the plate, when taken from the flask, will require little or no labor to make it ready for use. It is possible that some surplus material at the edges may have to be trimmed off and the edges smoothed, but the case is not properly prepared if more than this is necessary. The care and trouble involved in proper preparation will really save time, will absolutely avoid interference with the fit by the too free use of files, sand-paper, pumice, etc., and will insure a durable plate with a permanent imitation of glim color. More- over, the artistic taste of the operator may be exercised before the plate is molded more readily than afterward. " Paraffine and wax compound is used for the base-plate, according to directions before given, and the teeth arranged, the wax carved into the shape desired by means of carving tools, and made smooth. The piece is then invested in plaster, the usual grooves cut, the wax, teeth and tin foil being removed with the upper half of the flask in parting. The wax is then removed by means of boiling water, as before described, the 648 MECHANICAL DENTISTRY. tin foil, No. 60, used for covering the paraffine and wax plate, remaining upon the plaster, and the investment is now ready to be dried out preparatory to receiving the celluloid. "Drying the Cast and Investment.—To dry a plaster cast and investment, and keep them free from cracks and checks, is very difficult by the ordinary means, but with the New Mode Heater it can be done so perfectly as to permit their use in casting pure gold or gold alloys. " There are two ways of drying the investment in the New Mode Heater: first,by raising the temperature to 320°, keeping the hot box dry; second, by admitting steam to the hot box. The former method can be used when the investment is placed in the chamber before getting up steam. If steam is up, how- ever, either method may be employed. In using the dry-heat method, open very slightly the screw cap of the piston or valve stem, to permit the escape of the steam generated from the water in the plaster, being careful that the steam-valve is firmly seated, as otherwise all the steam made in the boiler will escape. In using steam for drying, admit the live steam into the chamber with the investment, by raising the valve from its seat, keeping the screw cap closed. The steam quickly per- meates the plaster, and in five or ten minutes the temperature of the plaster is high enough to convert the water in it into steam. As soon as the plaster is thoroughly heated, shut off the steam by closing the valve, and raise the screw cap very slightly, to allow that in the chamber to escape slowly through the small aperture at the side of the screw. In a few moments the cast will be perfectly dry, the steam escaping from the chamber, carrying with it that generated from the moisture in the plaster. Extreme care should be taken that the steam shall escape very slowly, as otherwise the plaster may be blown out of the flask into the oven by the too rapid expansion of its vaporized moisture. The completion of the drying process is known by steam ceasing to be given off at the screw cap, G. The drying may be facilitated by placing a small chip of wood between the two parts of the flask when it is put into the chamber, thus exposing a larger surface to the heat and allow- ing the moisture to escape more readily. CELLULOID BASE. 649 "Molding by Dry Heat.—When the investment is dried, remove it from the chamber and insert and carefully adjust the selected blank; replace the flask in the oven immediately under the screws; see that the two sections are so placed that the guide- pins will enter properly into the lugs; open the screw cap a turn or two to allow the escape of the gas from the hot box; turn down the large screw until it bears lightly upon the top of the flask, and close the machine. In less than five minutes the material will be sufficiently softened to permit the com- mencement of the molding. The screws will turn readily with the thumb and finger (using the smaller key-wrench), when the blank is properly softened. Close the flask gradually, stopping occasionally if the resistance is too great. Usually, if the tem- perature is about 300°, the flask can be closed in ten minutes; but if a very thick blank is used, the molding must proceed slowly; the small screws may be used to advantage, and more time, say thirty minutes, may be consumed. As soon as the flask is closed—unless a lock flask is used—the flame should be extinguished, the door opened, and the machine allowed to cool. If a lock flask is used, it may be removed and thoroughly cooled before opening it, the oven being meanwhile ready for another case. The cooling may be accomplished rapidly, if necessary, by placing the flask in water. When perfectly cold, remove the plate from the investment; it will be found envel- oped in the tin foil which had been burnished to the wax plate. Peel off the foil. The celluloid will present a hard, brightly- polished surface, received from its contact with the foil, and will need no further finishing than cutting off the excess of material and smoothing down the edges." In the use of a material, as a base for dentures, possessing properties so extremely sensitive to heat as that of celluloid, and so liable to suffer changes of color and structure materially affecting its usefulness by a misapplication of heat and faulty manipulation, everything that contributes to a better under- standing of its behavior in the process of molding must be of interest and practical value. The following experiments o Dr. J. Stewart Spence,of San Francisco, Cal., throw some addi- tional light upon the subject. He says:—- 650 MECHANICAL DENTISTRY. "Having just made more than thirty experiments with celluloid and the New Mode Heater, I have met with some interesting facts, of which, during two years' previous use of the apparatus, I was ignorant. The main results I will now give before relating the experiments, thus inverting the usual order of placing results last, for the sake of per- spicuity. " 1. Plaster investments require one, and a half hours to dry in the oven of the heater, with the thermometer at 400°, and half an hour more to raise their heat to 320°. Drying them over a gas-burner takes nearly as long, and loosens the plaster from the flask. A thermometer placed between the slightly separated halves of the flask in the oven indicates when this heat is reached, at which time a blank, previously prepared, should be expeditiously inserted. " 2. Celluloid may be molded in from five to ten minutes at 320°; in about twenty to twenty-five minutes it degenerates, becoming brown, hard, brittle and porous, and in twenty-five to thirty minutes it burns up. " 3. Celluloid will burn at either high or low temperatures, according to the length of time it is exposed to them, as well as their degree of heat. Thus it is unsafe to leave it at even a low heat for a long time, as in slow cooling. " 4. Celluloid is more liable to spoil if not under pressure, and those parts of the blank least subject to pressure are most liable to come out damaged. Therefore flasks should be closed with all expedition. "5. Celluloid, unless worked at a high temperature, so as to flow readily, and with well-hardened plaster, will press the model out of shape, and the teeth out of position. " 6. Steam brought in contact with heated celluloid makes it puff up and degenerate. " 7. Plaster retains heat longer than metal, and therefore plates left in the oven to cool may spoil or burn up even when the temperature of the heater has fallen to a low degree. "8. Tin foil discolors celluloid at a high heat, making it browner. " 9. Celluloid after molding is hardest at the surface, as may CELLULOID BASE. 651 be clearly seen in a plate that has been slightly overheated, it being porous internally, but very hard on its surface. "Instead of giving a copy of my record of these experi- ments, which would be unnecessarily prolix, I will give a con- densed account of them by series. " 1st Series. To test the heat of the oven. I placed in the dry oven a separate thermometer, which, with the door closed, registered the same as that outside; then reversed them with similar results. Removing the central screw from the top did not reduce the temperature perceptibly. Removing the door reduced it a few degrees. Removing both door and screw caused a rapid decrease from 320° to 290°. " 2d Series. To test the heat of oven with plaster in it. I filled a half flask with plaster and placed it in the oven, witb a ther- mometer on the floor beside it, of course closing the door, the outer thermometer standing at 320°. After twenty minutes the inner thermometer had reached only 300°, showing the cooling effects of the plaster on the air of the oven. Moved the thermometer on to the plaster, the thermometer fell con- siderably, and while the outer thermometer rose in thirty minutes to 440°, the inner reached only 290° ; steam was then admitted to the oven, and it ran instantly up to 340°; steam was then shut off, and the outer thermometer maintained at about 360° for thirty minutes longer, by which time the inner reached 320°. At this point some steam was let off, which ran the outer thermometer twenty degrees below the inner, showing that plaster is slow to part with its heat as well as to receive it. " Further experiments were made in drying plaster, both in the oven, with steam and without it, and out of the oven over a gas-burner; also with plaster mixed with pulverized pumice, and mixed with marble dust. It was found that in the oven with either steam or dry heat, and the outer thermometer at 400°, about thirty minutes were required to dry and heat a small half flask of plaster to 320°, and about two hours for a full flask. Done over a gas-burner, under an inverted flower- pot, a little less time was consumed, but the investments loosened from the flasks; under higher heats they became burnt and badly checked. Those mixed with pumice and 652 MECHANICAL DENTISTRY. marble dust took nearly as long to heat and became softer than the plaster alone, and so were thereafter abandoned. " 3d Series. Testing celluloid in the oven without the presence of plaster, steam or pressure. A piece of celluloid placed in the oven at 320°, the heat rising, burned, after slight swelling, at 360°. A second piece remained in thirty minutes with the heat at 320° ; swelled slightly, and crumbled to powder on being taken out. A third piece left in three minutes at 320° was taken out a little swollen and somewhat brittle and porous. " 4th Series. Testing celluloid in the oven with plaster and with moisture. A half flask of moist plaster was placed in the oven, and on it a piece of celluloid and a thermometer. . The outer thermometer starting from 320° rose to 440°, then fell to 360° in about sixty minutes, by which time the inner thermometer reached 320°, and the celluloid, after great swelling, ignited. (In the previous series of experiments the celluloid had swollen but about one-tenth as much as it did in these.) Next a half flask of previously dried plaster was inserted, and the inner thermometer raised to 340°, when a piece of celluloid was dropped in, and burned in five minutes. A second piece at about 330° puffed up in ten minutes, and would probably have exploded in five more, if I had not varied the experiment by admitting steam to test its effects, which were a greatly in- creased swelling and then gradual shriveling to a thin wafer. (That steam does not produce ignition was also demonstrated elsewhere, when its admission ran the inner thermometer up to 340°, and yet afterward, when the steam was shut off, the celluloid burned at 320°.) In the next test the dry half flask was again used, but the outer thermometer was lowered to 320°, which ran the inner one down much lower, but in forty minutes they tallied, during which forty minutes the celluloid after the first fifteen minutes began to puff, and in ten minutes more had reached full size, and then for fifteen minutes slowly shrank and then exploded. " Both thermometers being now at 320°, a piece of blank was left in fifteen minutes, and on being taken out crumbled to powder under the slightest pressure. A second blank, in twenty-five minutes, at 300°, came out not crumbling so badly. CELLULOID BASE. 653 A third at 280°, for thirty minutes, was slightly swelled and somewhat brittle and porous. " 5th Series. Testing celluloid in the oven with pressure and plaster. A full flask of plaster was placed in the oven, and its temperature raised to that of the outer thermometer, 320°; then a piece of celluloid was placed in the flask, which was closed down in three minutes, and in five more the piece was removed from the flask in perfect condition. A second piece was then inserted, closed in ten minutes, and removed from the oven, and in five minutes more opened in perfect condition. A third piece was left in twenty minutes, and in five more opened in perfect condition, not even discolored. A fourth piece was given twenty-five minutes in the oven, and ten more before opening the flask, with disastrous results: it had crumbled to a brown powder. " This fifth series of tests shows that the material in question remains perfect under pressure longer than without it. But it is to be remembered that the investment here used must have lost some of its heat while out of the oven. Later trials seem to indicate twenty minutes as the longest time that celluloid can safely be left at 320°. As a side issue, the cohesion of the mate- rial was tested during this series; freshly-filed surfaces were placed together, and apparently joined, but they separated under a strong strain. "6th Series. Testing the effect of steam on the celluloid at 320°. The same investment was used as in Series 5, and the flask closed in ten minutes, when steam was admitted. In ten minutes more the blank came out spoiled, being disintegrated, whitish and sticky. I have seen celluloid take on this soft and white condition when heated in water above 270°. "7th Series. Testing the flowing qualities of celluloid at 320°. A piece of celluloid was placed in a flask heated to 320°, no cavity being left in the plaster to receive the celluloid. Closed in ten minutes. It sunk a bed for itself in the hard plaster, flowing but little. This is a hint as to the cause of misfits, raised bites, and thickened palates, of plates molded with soft plaster and low heats. " 8th Series. Testing the effects of quick closing. A full blank 654 MECHANICAL DENTISTRY. was placed in a full flask of plaster heated to 320°, and closed so that the halves of the flask came together on one side considerably sooner than on the other. Gave it over fifteen minutes in the oven. When opened it showed, as expected, the side of the plate which had been the latest closed, porous and brittle. As a side issue in this experiment, tin foil of two thicknesses, 18 and 60, were placed side by side on the blank, and when peeled off the surface below was of a browner color than the adjacent celluloid. " I would hint at the possibility of the celluloid which oozes from the flask, and touches the wall of the oven, being ignited thereby in some instances. A deep excess-chamber should be cut around the model to prevent this. Moreover, this escaped celluloid, not being under pressure, is doubtless more liable to burn. "Celluloid hardens on being subjected to dry heat,but much of this is not desirable, as its hardness is*external, while inside it becomes porous, and when thus hardened is very brittle. Celluloid will burn under water, as demonstrated in a vulcan- izer at 320°. "Thin edges of celluloid will soften in hot drinks in the mouth. Thus, the festoons of gums left thin will shrink from the tooth, producing what may be termed a free edge of cellu- loid gum, under which dirt deposits, and shows through the semi-translucent celluloid. This is prevented by making the edges of the festoons of proper thickness. Another error fre- quently seen is that of cutting away the interdental celluloid gum (contrary to nature), thus forming cavities difficult to cleanse by the brush of the patient, and producing unsightly discoloration at those points. "The principal objection to celluloid is that after a year or two in the mouth it loses its beautiful color, and becomes of a dull vermilion shade, or even black. This will probably re- main the chief objection to it. That it is not so tough nor so elastic as vulcanite, and that in consequence it wears away and loses its smooth surface in the mouth, and is unfitted for clasps, and that it is a little more difficult to work than rubber, would not prevent its popularity, if it were not for this discoloration. CELLULOID BASE. 655 However, the loss of color does not always extend far into the plate, and much of it may be quickly removed with a brush- wheel and pumice." Repairing.—This is readily accomplished in the following manner: Cut away the plate, and fit in the new teeth or block. Dove-tails or holes may be made, but they are not essential. Always, if possible, before flasking, fit a new piece, larger than the portion cut away, to the plate as closely as possible, and let it come near to the added teeth; then, having the surfaces clean, cement it fast with spirits of camphor, or a solution of celluloid and camphor. Allow it to dry, after which the new teeth should be waxed into place. Invert the piece of the flask, Fig. 426. No. 2. covering the whole plate and teeth in the plaster, except the added piece, which should be left at the bottom of a well or depression in the plaster. The above cut (Fig. 426) will show the manner of repairing, and make it as plain as can be done in print. No. 1 shows the first step in the process, the plate being cut away and the new piece (shown at "a") fitted and cemented in place. After drying a short time (allowing it to stand a few hours or over night, if convenient), fit the new block to its place, leaving as little space as possible between the plate and block; this space is to be waxed up to keep out plaster when investing. No. 2 656 MECHANICAL DENTISTRY. shows the piece invested, the whole plate and teeth, except the new piece "a," being covered deep in the plaster, which is trimmed as shown. The upper part of the flask is now put in place, and filled in the usual manner. On opening the flask boil out the wax. Then lay another piece of celluloid, or a ball of tin foil, or moistened blotting-pad—in fact, anything that will produce pressure, upon the piece "a," and heat up and press as usual. In this way the new piece becomes a part of the plate by the cementing process, before the pressing is done, and will not scale or separate. If neatly done, the line of junction will be scarcely observable. The sharp edge of the plaster at the bottom of the well or depression should be trimmed out and well rounded, as otherwise these edges are liable to fracture and get into the plate. If the new block or tooth is separated from the plate, so that it has no support, and is liable to be pushed down, it should be supported by crowding a small bit of cellulcid under it before beginning. The new piece may be placed in position after opening the flask, a few drops of spirits of camphor added, and the case pressed as before; but union by this means is not nearly as certain. There is no certainty about uniting pieces in the ma- chine. It may be done, or it may not. But by cementing well-fitting or freshly-filed surfaces together outside the flask, perfect union may always be had, and pieces added wherever desired. In investing, the plate should always be placed in a position the reverse of that indicated by the cut on page 630, in order that a direct downward and not a side pressure may be had. Care should be taken to avoid air-bubbles in the plaster, and to pour it smoothly. If the plate is of sufficient thickness, the repair may be very nicely made without adding any new material. Fit the new block without cutting away more of the plate than absolutely necessary. Invest the plate, leaving the lingual side exposed, but covering the teeth; on opening the flask, lay over the ex- posed plate one or more thicknesses of wet, thick, brown paper, blotting-pad, or unvulcanized rubber, fitting closely to the teeth and having it thickest in the centre, and press as usual. By this means the plate will be spread up to the new teeth, which VULCANITE BASE-PLATE FACED WITH CELLULOID. 657 will be firmly united. Loose teeth, if any, on the plate may be tightened by the same means, having been waxed in place, and the wax afterward thoroughly boiled out. Some dentists attempt to mend in this way without using anything to pro- duce pressure, depending upon the swelling of the plate to fill the vacancy. This would be certain to injure the density of the plate. To remove teeth, heat the plate in boiling water or glycerine, when they will easily come off. Rubber plates may be very nicely repaired with celluloid, but as there is no union, dove-tailing or drilling holes is neces- sary. Finishing.—This is accomplished with the use of the same instruments used in rubber cases. The final polish may be given first with pumice-stone, and afterward with whiting or Vienna lime. Dr. H. D. Knight, of Lancaster, Pa., recommends a polish obtained by rubbing with an old cloth wet with cam- phor. This may be valuable between teeth, and in places inaccessible to the brush-wheel. In finishing, care should be taken not to heat the plate by friction, as by so doing the surface may be injured, or the plate sprung out of shape. VULCANITE BASE-PLATE FACED WITH CELLULOID. The above method of constructing an artificial denture, designated by the inventor as the " New Mode Continuous- Gum " process, provides for the use of single porcelain teeth without artificial gums, the latter being represented by the celluloid facing. This expedient is most esteemed by those who regard rubber as a more suitable material for a base than celluloid, and who, in the use of the former, are unable to meet the requirements of a certain class of cases with either single gum teeth or sectional blocks. In this combination work, which admits of an optional arrangement of each individual tooth, the conditions are secured which better enables the operator to effect such arrangement of the teeth as will best serve the purposes of mastication and aid in restoring the customary facial contour and expression of the individual. Still other advantages are claimed for this 42 658 MECHANICAL DENTISTRY'. method, namely, that the rubber is stronger and more elastic, and, being harder, the pins are less liable to draw or loosen, while the same property diminishes the liability to mechanical abrasion of the palatal surface in mastication, and, lastly, that in case of accident to the teeth they may be replaced with the use of celluloid, thus obviating entirely the necessity of re-vul- canizing, a process which always impairs the structural integrity of the rubber. The first step in the process of constructing this kind of work consists in molding the rubber base-plate, with the teeth attached. All the preliminary processes, including the arrange- ment of the teeth, are the same as those practiced when rubber alone is used. The teeth employed are those manufactured expressly for continuous-gum work and celluloid, as shown in Fig. 427. Fig. 375. In waxing up the case, all the exterior surfaces of the teeth and marginal portions of the trial plate are left uncovered, and a strip of wax arranged all along the external border of the wax plate to form a groove for the celluloid, as shown in Fig. 427. The excavation thus formed exteriorly should extend inwardly into the interdental spaces far enough to secure anchorage for the celluloid in connection with that obtained by the grooved border. The space or spaces for the celluloid facing being thus provided for, the palatal portion is properly contoured, the case flasked, packed and vulcanized in the usual manner. The piece, when removed from the flask, will exhibit an undercut groove along the border, and the > external portions of the crowns and roots exposed in the manner shown in Fig. 427. VULCANITE BASE-PLATE FACED WITH CELLULOID. 659 The second step in the operation consists in molding the celluloid facing. The following is the method of forming the matrix and molding the celluloid: Fill up all the space between the rimmed border of the plate and the crowns of the teeth with wax and paraffine, as being preferable to wax alone, and then contour it exactly as required in the finished piece; cover with tin foil, and stipple the surface in the manner heretofore described. The case thus prepared is ready to be invested for the purpose of obtaining the matrix in which to mold the Fig. 428. celluloid. In so doing, fill the lower section of the flask partly with plaster, and also the palatal portion of the plate, and then place the latter in the flask with the teeth upward, raising the front part of the plate somewhat, giving it a downward in- clination posteriorly, in order that the upper section, when the investment is completed, may be detached without dragging. The plate should not be imbedded in the plaster beyond the grooved margin, making the line of separation on the outside 660 MECHANICAL DENTISTRY. along the border from heel to heel of the plate. Additional plaster is now poured in, covering the entire palatal face of the plate and crowns of the teeth, leaving only the outer portions of the latter and the plate exposed. When the plaster sets ■ somewhat, pour in more plaster around the inner edge of the flask ring, forming a ridge, and also a corresponding groove or space between it and the plate. The piece thus invested will present the appearance shown in Fig. 428. The surface of the plaster is now varnished, and thin oil applied to all the sur- faces. When the wax facing is covered with tin foil, the latter should not be oiled, as it is intended that this shall adhere to the plaster when the flask is separated. The investment is now completed by adjusting the upper section of the flask and Fig. 429. filling it with plaster. When sufficiently hard, the sections are carefully separated, and the wax thoroughly removed with boiling water. The tin foil will remain adherent to the plaster in the upper section. Select a celluloid blank of suitable size and saw off the outer rim, as shown in Fig. 429. Dress and carve this to near the size and form of the space to be filled, having some excess of material. Having first softened the rim thus prepared by immersing it in boiling water for a few moments, remove, press it well into the space provided for it, and hold there until rigid. Place the two sections of the flask together in their proper relation, introduce into the oven previously heated, ZYLONITE. 661 and close the flask in the usual way. When the piece is re- moved from the flask, and the tin foil removed by peeling it from the surface to which it will adhere, little will be required in the way of finishing except to remove surplus material at the necks of the teeth and borders of the plate, and final smoothing and polishing at these points. If the facing ma- terial has been stippled, the finished piece will present the appearance shown in Fig. 430. The above process is also applicable to gold and cast metallic plates. ZYLONITE.* " A modified form of celluloid has been recently introduced under the name of zylonite, the working results of which appear to show a great difference in quality. Zylonite, like celluloid, Fig. 430. is composed of pyroxylin and camphor, but in different pro- portions, being, it is claimed, a chemical combination, while celluloid is a mechanical mixture. " Possessing translucency, the effect of zylonite in the mouth is very pleasing, and, so far as it has been tested, promises to be more durable than celluloid, without the tendency to warp, or to change color when ordinary care is taken in its manipu- lation, which is the same as for celluloid. The zylonite blanks are uniform in color, and although this material requires the same amount of pressure to mold, it flows with a more perfect sharpness of outline than celluloid, and apparently does not disintegrate." * Harris' Principles and Practice of Dentistry. CHAPTER XVIII. ATTACHING PORCELAIN TEETH TO A METALLIC BASE WITH RUBBER OR CELLULOID. The following method of attaching porcelain teeth to a metallic plate by means of rubber or celluloid, though but little practiced heretofore, is attracting more attention than formerly, and is eminently deserving of more favorable con- sideration and general adoption, by reason of its conspicuous and acknowledged merits, than it has ever yet received. The credit of its first introduction to the notice of the profession is due to Dr. P. G. C. Hunt, of Indianapolis, Ind., who practiced the method as early as 1859, and whose published descriptions of the manner of preparing the plate base, substantially the same as that for which Mr. S. D. Engle, of Hazleton, Pa., obtained letters-patent some years later, were given in the first edition of this work. In commenting on this method, Professor Charles J. Essig very justly remarks that, by the means here indicated, we are "able to produce an artificial denture embracing all that is good in metallic and vulcanite work, at the same time avoiding the great defects of each." That it possesses marked advantages over the method of . attaching teeth to a metallic plate-base by soldering is unques- tionable. The warping and consequent change in the form of the plate incident to soldering, so inseparable from the older method of attachment by means of stays or backings, is wholly avoided; the strain upon the platina pins is greatly lessened by reason of the perfectly adapted rubber or celluloid socket in which each tooth or block securely rests; the liability to fracture of the teeth from concussion or violence is materially diminished on account of the pliable nature of the attaching material used; a nearer approximation to the natural form of the ridge or gum on the lingual side of the plate is secured; the rubber or celluloid, penetrating all the joints and openings 662 METALLIC BASE WITH RUBBER ATTACHMENT. 663 between and beneath the teeth, renders the piece wholly im- pervious to the oral secretions, making it, in point of cleanli- ness and purity, equal to continuous-gum work; the facility with which injury to the teeth may be repaired; the practica- bility of remodeling the piece without impairment of the teeth or plate; its susceptibility of receiving a final finish excelled by no other method in point of artistic beauty;—these are among the qualities which commend this method of substitu- tion as one of peculiar merit and excellence. In mounting teeth by this method, preference should be given to either gold, platinum or cast metal as a base. When silver is used, the plate should be made from refined silver alloyed with platinum, with the additional precaution of inter- posing a layer of tin foil between the rubber and plate, an expedient not necessary when celluloid is employed. Aluminum has a limited adaptability to this mode of substitution, but requires special treatment in its preparation for the purpose, a description of which will be given in connection with the manner of preparing the plate. The manipulative details concerned in the construction of an artificial denture by the method under consideration are thus described by Dr. Hunt:— " Take the impression, make metallic dies, and form the plate as for work in the ordinary way. After fitting the plate in the mouth, get the articulation, the fullness and length of the teeth, remove the wax and plate from the mouth and make the plaster articulation. If a full set, after separating the articula- tion, and before removing the wax from the plate, take a small light pair of dividers, set them say one inch apart, and with one point following the margin of the wax representing the cutting edge of the teeth, and the other point marking permanently the plaster, you have always in the dividers so set a gauge for the length of any particular tooth. A convenient sub- stitute for the dividers may be formed from a piece of wire of convenient length, one-half the diameter of a common ex- cavator, by suitably twisting its middle for a handle, and its ends being sharpened, and pointing in the same direction, one or one and a half inches apart. 664 MECHANICAL DENTISTRY. " Thus far we proceed as we do for ordinary gold work. We will now suppose the teeth ground and jointed, leaving as much space between the teeth and plate as the plate will admit of. We next mark with a sharp-pointed instrument on the labial surface of the plate each point where it is necessary to place a loop for purposes hereinafter described. Then apply wax to the external or labial parts of the teeth and plate in any man- ner sufficient to retain the teeth in position, remove the wax from the lingual parts of the teeth and plate, and mark the position on the metal where it is desirable to insert loops, re- move the teeth and wax, and with a small bow-drill make holes through the plate at the several points previously deter- Fig. 431. mined on for the attachments, about the size of the ordinary plate punch-hole, take a wire, or ordinary gold plate, cut in strips, say from a half to one line in width, being governed by the amount of room there is under the base of the teeth, and with small, round-nosed pliers, bend the strip around, grasp both ends with square-nosed pliers, draw the round-nosed pliers from the loop, still grasping the square-nosed pliers with the left hand, and with a hammer strike the top of the loop a sufficient blow to keep the ends from springing apart. Cut off the ends, and dress down to fit the holes in the plate, after which solder on charcoal or other suitable substance without investment." METALLIC BASE WITH RUBBER ATTACHMENT. 665 By reference to Fig. 431, which illustrates Mr. Engle's method of providing attachment for the rubber to the plate by means of bent or hooked wires soldered to the base, the sub- stantial identity of Dr. Hunt's mode of forming loops for the same purpose will be apparent. With this digression, we return to Dr. Hunt's instructions :— "Pickle, dress and polish that portion of the plate to be exposed to view. Bend and flatten the pins, arrange the teeth according to the articulation, waxing so as to cover up the loops if practicable; the loops should be placed as near the base of the teeth as possible, the rubber forming when finished a part of that general concave shape which is desirable in upper dentures, and which is not possible to obtain with the ordi- nary soldered work. Then with silicate of soda paint the joints, to keep the rubber from forcing in where it would show after vulcanizing. Flask, vulcanize, and finish up as usual. The advantages of this style of work are obvious. With this you have work as cleanly as the continuous gum, decidedly more so than the very best single gum or block-work soldered in the usual way; again, it is very much stronger, less liable to break- age, both in and out of the mouth, as the rubber gives a per- fect base and support for the teeth to set upon. By this method there is no springing of plates. As your plate fits the mouth when the articulation was taken, so will be the fit when the case is completed. " On the labial edge of the upper plate the rubber may be allowed to project beyond the edge, if desirable, and it will be found in many cases exceedingly satisfactory to do so, and allow the rubber to be of considerable thickness near the alas of the nose, where the loss of the cuspidati may leave a want of support to the soft parts adjacent, and which in this manner can be readily corrected. If the rubber extends upward so far as to irritate the muscular structure, a few minutes will be sufficient to make the necessary alterations. In all such cases where we have control of our patients, we place the denture in the mouth before finally polishing, so as to deter- mine as accurately as possible the limit to which extension upward may be carried. 666 MECHANICAL DENTISTRY. " The neatest work on this principle is made by carving blocks, giving to the lingual surface that regular concave form which is desirable. In this no platinum pins or loops are necessary, but that half of the matrix on which the blocks are carved, large metallic pins are so arranged as to be hid from view in the tooth body. Different sized pins may be used, as large as the nature of the case will admit. In short, we make the holes in the block similar to those in pivot teeth, where there is not sufficient room in the block above the tooth (or below if an under) to allow the pins to run into the body of the teeth. After burning, grinding and fitting, get the position of the holes in the blocks relative to the plate, and drill through the plate as before, and instead of loops, solder gold wire of suit- able size and length, say a very little shorter than the depth of the hole in the blocks, and two-thirds the diameter thereof; the wire should have a screw-thread cut on it, or that which is just as good, and more expeditious, barb or cut with a sharp knife. At this point of the manipulation, if it is desired that the rubber should extend beyond the labial or buccal edge of the metallic plate, place as' many loops at different points as are sufficient to retain it with firmness, after which polish the plate, wax, and proceed as before described. If you desire no rubber beyond the blocks, the roughness of the holes in the same, and the barbed points on the gold wire when properly packed and vulcanized, will give ample strength and firmness to the case, and if care has been used in the entire manipula- tion, you will have, when finished, but a thin line of rubber exposed to view. " In partial cases, if of gold base, solder on loops, as before, for the retention of the teeth, and if there are to be any clasps, make them of rubber, uniting them, as the teeth, with loops. If the ordinary plate teeth are used, it is frequently necessary to back them to give better retaining-points for the rubber. If blocks are to be burned, insert loops of platinum plate in the shape of the letter U in place of the platinum wire pins. In consequence of the affinity of the sulphur in the vulcanite for silver, plates of that metal should not be used." The following unique and original method of casting a metal METALLIC BASE WITH RUBBER ATTACHMENT. 667 base-plate and fastenings and hooks in a single piece, is thus described by Dr. Norman W. Kingsley: "The plate is formed of a thin sheet of wax set up on the plaster model, but before it is flasked for casting I take a dozen small gimp tacks, with half- round heads, and set them in a row upon the ridge of the lower jaw, with their heads just embedded in the wax, and then flask the piece. In flasking it, I use plaster and sand, in the pro- portions of about three parts of sand to one of plaster. This gives a fine surface when it comes in contact with the wax in making the mold, and it is sufficiently porous to dry out quickly. When the flask is opened, the wax is readily re- moved; the tacks are pulled out, and when the casting is made, the spaces that were occupied by the tacks are filled with the metal, so that we have a plate with a row of tacks of the same metal, which can be easily bent for attachments, standing around upon it." If gum sections are used in connection with a plate formed in the manner just described, vulcanite may be employed as a means of attachment, but plain single teeth are equally admis- sible in the use of celluloid. The particular alloy used by Dr. Kingsley in casting plates, and of which he speaks in terms of high commendation, consists of pure tin and bismuth, in the proportion of one pound of the former to one ounce of the latter. The following method of preparing aluminum plates for the attachment of the rubber, was communicated to the author by Dr. J. W. Hollingsworth, of Greencastle, Indiana, an intelligent practitioner, who has had long and extended practical expe- rience in the various modes of working this metal for dental purposes, and who says of the following mode of procedure, that " it is the most practicable and the most easily manipulated method that I have yet seen." The following is the manner of preparing the plate as described by Dr. Hollingsworth: " Perforate the ridge of the plate at proper points and intervals; then pass through these perforations, from the inner surface of the plate, headed pins made of aluminum, which, after replacing the plate with the pins back upon the die, we shrink down to permanency with 668 MECHANICAL DENTISTRY. a hollow punch. The punch must be made with the hole not quite equal in depth to the length of the extruding portion of the pins, and slightly bell-mouthed. This riveting process forms seriate studs or pins, which may be bent or flattened with pliers in any way to suit the requirements of the case." When celluloid is used for purposes of attachment in the case of upper entire dentures, the palatal portion of the blank should be cut or sawed away, leaving only the ridge portion to be used, and this should be trimmed, if necessary, so as to have but little excess of material. The ordinary full blank may be used for lower cases, observing the same precautions in regard to quantity of material. When the blank is thus prepared, the subsequent manipulations are the same as those described in connection with the celluloid base. It may be observed that, when rubber or celluloid is used, it is better to dispense with the plaster model in forming the mold or matrix, and proceed as follows: When the teeth are arranged, and the required contour and fullness given to the wax drafts, fill the lower section of the flask with plaster, and (having also filled the plate with the same) imbed the plate in it, making the dividing line on the external rim of wax. When the plaster has hardened, and the other section formed, and the two afterward separated, the metallic plate will remain in the lower section, and the teeth in the upper. When using celluloid, plain teeth may be advantageously employed, the former representing the gum; this gives perfect freedom in the arrangement of each separate tooth in the den- ture, an optional disposition the importance of which cannot be overestimated. CHAPTER XIX. CAST METAL BASE. Cheoplastic Process.—The method of mounting artificial den- tures by what is familiarly known as the " cheoplastic process," in which the base consists of certain metallic compounds or alloys in cast form, has comparatively but limited application in prosthetic practice. The method, as commonly practiced, is rarely applied to full upper cases, more frequently to partial upper pieces, but chiefly to lower dentures in cases of unusual absorption of the alveolar ridge, requiring increased weight to secure adequate stability of the substitute. The alloys in most general use for this purpose are those compounded by Drs. Wood, Weston and Watt, whose names are a sufficient guar- antee of the suitableness of these several alloys for the purpose. The construction of a denture by this method is readily accomplished by any one familiar with the working of vul- canite or celluloid. The manipulations concerned in the form- ation of a mold or matrix are, in general, the same as those employed in forming a matrix for rubber or celluloid. The model and investing material, however, must be of such sub- stances as maintain their integrity of form perfectly under the heat necessarily applied in thorough drying of the case and contact of molten metals. Simple plaster, on this account, is unsuitable, either for the model or investment, and it is cus- tomary, therefore, to add to it, in relatively large proportions, such substances as undergo but little, if any, change of form when exposed to the necessary heat. Those most commonly employed are finely pulverized pumice-stone, marble dust, soap- stone powder, or clean white sand. In the use of either of these substances, only enough plaster should be added to give to the molding material sufficient body or strength necessary to provide against defacement in handling, say one part plaster to three of sand, which is the mixture generally employed. One of the best adapted flasks for molding and casting pur- 669 670 MECHANICAL DENTISTRY. poses, contrived by Prof. George Watt, is exhibited in Fig. 432. The piece, properly prepared by careful contouring of the wax or paraffine, is then flasked in the same manner as when pre- paring a mold for vulcanite. When the sections of the flask are separated, grooves or gateways should be cut, extending from the posterior and lateral margins of the mold to the openings on either side shown in the figure, thus providing for the ingress and egress of the melted metal when poured; after which all traces of wax should be thoroughly washed out with boiling water. Fig. 432. The sections of the flask are now adjusted to each other, and tightly clamped to prevent the escape of metal when poured. Before casting, the mold should be thoroughly dried by ex- posing it for two or three hours to an oven heat, and the tem- perature, at the moment of pouring, should be raised to about that required to fuse the alloys mentioned, or about 400° to 440° F. In pouring the metal into the mold through one of the lateral openings, the metal should rise freely and quickly into the opposite one, and if bubbling occurs, which will never CAST METAL BASE. 671 happen if the plaster has been sufficiently dried, the flask should be lightly tapped on some hard surface until the ebul- lition ceases, thus insuring a more certain intrusion of the metal into all parts of the mold before solidification takes place. Dr. Weston has devised a casting flask (Fig. 433), the two Fig. 433. sections of which form an encircling band with the sides, or top and bottom, open, and which are closed securely with screw-bolts. This form facilitates the escape of moisture from the plaster investment in the process of drying. When the piece is quite cold, it may be readily removed from 672 MECHANICAL DENTISTRY'. the flask by soaking the investing material for a few minutes in water. All superfluous metal is removed with suitable in- struments, and all surfaces except the palatal face smoothed and polished, first with Scotch stone or fine emery cloth, and finally with chalk used upon a brush-wheel. If there are any narrow spaces or interstices, not affecting the integrity of the plate, that are not completely filled at the time of casting, such imperfections, Dr. Kingsley suggests, may be readily and perfectly repaired with amalgam. There are other practicable methods by which cast metallic plates may be utilized to advantage, and their application to the needs of the practitioner greatly extended. There are many cases of absorption in which a lower denture constructed en- tirely of cast metal would be objectionable on account of excessive weight. In such cases, a plate of sufficient thickness to secure the required stability may be cast, and the teeth sub- sequently attached with rubber or celluloid, as described in connection with swaged plates; or the base-plate may be cast in the form of the rubber base described in connection with the New Mode continuous gum, and faced in the same manner with celluloid,—either method, while securing the requisite weight, admitting also of the use of single plain teeth. GOLD ALLOY CAST BASE. The compound of gold, silver and tin, in varied propor- tions in connection with specific and original methods of cast- ing dental plates, devised and patented by Dr. George F. Reese, of Brooklyn, N. Y., has attracted attention as a possible sub- stitute for the plastic vegetable substances so commonly em- ployed as a base for artificial dentures. After premising that the methods in common use for cast- ing alloys were not applicable to one having the molecular properties of Reese's compound, the inventor says he was led, after multiplied experiments, to adopt the plan of which the following is a description :— The impression is taken with plaster, to which salt or sul- phate of potassa has been added, and the model obtained from this with pure plaster. Upon this the teeth are arranged. For GOLD ALLOY CAST BASE. 673 the trial plate, gutta-percha, paraffine and wax, or modeling compound, may be used. When satisfaction in the occlusion is attained, then the case is returned to the model, and the waxing around the labial and buccal borders of the teeth com- pleted. That portion of the trial plate which covers the pal- atine surface is now removed, so that the pins of the teeth will be nearly exposed, allowing the wax which is under the gums to remain. That the plate, after casting, shall not be too cumbrous, the trial plate, which has been removed, must be substituted with two thicknesses of French flower wax, cut carefully to the model, and pressed down closely with the finger Fig. 434. in a manner that no wrinkles will appear to mar the beauty of the work. Fig. 434 represents a case thus prepared. The dotted lines show the borders of the thin wax. B, A and C represent nipples of solid wax, fixed to the posterior border and to the tuberosities; A and C being the places of exit for the molten metal into the waste pockets, and B the place of entrance of the metal from the pouring-gaine. The case is now transferred to the small brass flask, r, Fig. 435, the sections of which having been well oiled, upon 43 674 MECHANICAL DENTISTRY. the inner surface, to facilitate their removal from the invest- ment. Either section is then placed upon a plate of glass and plaster poured into it until half filled. The model, as pre- pared, after being well saturated with water, is imbedded in this single section, allowing the teeth and gums to remain un- covered. Set on the counter-part of the flask and add more plaster along the posterior border until the nipples are reached or slightly covered. After this has set, the upper section may Fig. 435. Case ready for the completion of investment. be removed and the surface of the plaster covered with a thin solution of shellac, Elliott's parting fluid or vaselin. Return the section and complete the investment. Fig. 435 shows the case thus made ready. After a proper time place the flask in hot water that it may be separated without injury. When separated, wash away all the wax, and, by means of gentle tapping, remove the flask rings from the investment and set them aside. The depressions GOLD ALLOY CAST BASE. 675 formed by the nipples may now be extended through the plas- ter to the external edge; or, if the circumstances of the case make this impossible, the channels may be made at the line of division between the two sections, as shown by the dotted lines in Figures 436 and 437. Externally, the channels, D, E, F, Fig. 436. Fig. 437, should be neatly countersunk and varnished with shellac to receive the pockets. The latter are made of the French wax by warming and wrapping the same around a cone-shaped stick, and the base and apex of the cone neatly 676 MECHANICAL DENTISTRY. trimmed of all inequalities. These pockets should be about one and a half inches lorfg, and about half an inch diameter at the base, and an eighth of an inch at the apex. The pouring- gaine is made in the same manner, but should be smaller in diameter at the base, and about two inches long. After re- moving these wax covers from the molding-sticks, the larger ends of each should receive a thin wax cover secured to its place, and made water-tight by flowing hot wax along the line of junction, after the manner of soldering. Trim the covers, then place the smallest ends of the large cones in the Fig. 437. Upper or counter section corresponding to Fig. 436. D, E, F, channels for entrance and exit of metal. countersunk channels at the tuberosities and the small cone in the middle hole, and secure them with melted wax. Fig. 436, d', e',f, shows the pockets thus attached. Should the channels have been made through the solid plaster of the lower section, as in Fig. 436, then the upper section, Fig) 437, need not be joined to it until after the pockets are secured to their places. Should, however, the channels have been made upon the line of division, then the sections must be joined before the pockets can be attached. GOLD ALLOY CAST BASE. 677 The case is now ready for a second investment, which is done in a flask sufficiently large to embrace the case as it now presents. Fig. 438 represents the construction of the large flask. One section of the same is placed upon glass and about half filled with plaster. The case, having been well soaked with cold water, is laid carefully upon the plaster, allowing the long cone to rest in the notch at the heel of the flask, and the waste pockets to become imbedded in the plaster. Immediately put the other section of the flask in place and complete the invest- Fig. 438. ment by filling with plaster the uppermost section to fullness. Of course, there will be no division of the sections as was the case in the former flasking. After solidification, the pouring-gaine must be neatly trimmed and countersunk, and great care must be exercised that no dirt be allowed to enter the channel. The wax, which is imbedded in the plaster, and which forms the waste pockets, will be entirely absorbed, and no trace of it will be seen upon opening the flask. 678 MECHANICAL DENTISTRY. All is now ready for drying. This is done in an oven specially prepared for the purpose, but it may be accomplished in any way to be chosen by the manipulator. An ice-cold mouth mirror placed over the opening of the pouring-gaine will detect the slightest moisture which may remain, and until this is entirely dispelled, the casting should not be attempted. There are several grades of the gold alloy, as compounded by Dr. Reese, which require a heat registering from 600° to Fig. 439. 700° Fah. to melt, but a higher temperature than this must be attained before pouring, in order to secure a satisfactory flow. At 900° rapid oxidation takes place. This, of course, should be avoided. The alloy may be melted in an ordinary iron ladle or crucible over a gas or other flame, and should be poured while the mold is hot. After the lapse of an hour or two, or until the cast is suffi- ciently cooled to insure the integrity of the teeth, it may be GOLD ALLOY CAST BASE. 679 placed in warm water, when the investment can be easily removed. Fig. 439 represents the cast after removal. The surplus metal may be separated, along the dotted line S, with a ribbon saw, after which the denture is ready for the pumice wheel and brush. Fig. 440 represents the finished case. Repairing.—The process of repairing broken plates is, in principle, the same as above. A flask, specially constructed by the inventor, is used for this purpose, whereby a single investment suffices. Suppose, for example, a plate is broken, from the labial to the posterior border, along the median line; the broken edges are scraped clean, and a separation made of about an eighth of an inch. The parts are then adjusted upon Fig. 440. the model, and the space between the approximate edges filled with wax. At each extremity of the fissure a pencil of wax, an eighth of an inch in diameter, and one and a half inches long, is securely attached, perpendicularly, to the palatine sur- face, and the whole surrounded with plaster to the depth of one inch. Thus will be constituted two sections, which are separated, and the wax washed out. The external ends of the channels, formed by the pencils, are then countersunk, and into each is inserted a wax cone, the one forming a pouring- gaine, and the other a waste pocket. The latter should be en- tirely covered by the plaster. The whole is now invested in the repair flask, and subsequently submitted to the process of diying. 680 MECHANICAL DENTISTRY. Dr. W. S. Elliott, of New York, has taken advantage of the method above described, to overcome the difficulties attending the construction of continuous-gum work. To maintain a perfect adaptation of a swaged plate seems almost impossible, in consequence of the springing of the plate in the furnace. To avoid this difficulty, the following plan is suggested: The plaster model is first covered with two thick- nesses of French flower wax, carefully adjusted. From this a metallic die and counter-die are made, and a very thin (No. 32) platina plate is swaged to fit the waxed model. The labial border need not be returned as in ordinary cases. Upon this the teeth are arranged, and the case is transferred to the fur- nace for biscuiting and enameling. After proper annealing, it is replaced upon the model and waxed up, on the labial and buccal borders, over the edge of the plate; then flasked, the wax removed, and the metal cast upon it in the manner here- tofore described. Danger of checking the enamel is associated with the process; but success has attended the effort, and it is hoped that present experiments will insure perfect and uniform results. CHAPTER XX. DEFECTS OF THE PALATAL ORGANS, AND THEIR TREATMENT BY ARTIFICIAL MEANS. DR. KINGSLEY''S ARTIFICIAL VELUM AND PALATE.* Palatine Defects.—Defects of the palatine organs may be divided into two classes, viz., accidental and congenital. The first includes all loss of substance in either hard or soft palate by disease or otherwise. Such defects are not uniform in locality or extent, being sometimes but a simple perforation of the palate, and at others involving the destruction of the entire soft palate, a considerable portion of the hard palate, the vomer and turbinated bones, and the loss of the teeth. The second class includes all malformations, from the simple division of the uvula to an opening through the velum, pala- tine and maxillary bones, and a division of the upper lip, thus uniting throughout their entire extent the nasal passages with the oral cavity. These malformations are quite similar in character, but not uniform in extent. They ma}' be said to begin with the uvula, and in the uvula and velum always occupy the median line; but as the defect progresses anteriorly, it may deflect to one side or the other of the vomer, and follow the nasal passage through the lips, leaving the vomer articulated with the palatine bone on one side; while in other cases the deformity seems to follow the median line, and thus involves both nasal passages, and terminates in a double fissure of the lip. In both classes (accidental and congenital) the faculty of dis- tinct articulate speech is seriously impaired by defects of any extent. In ordinary cases of congenital deformity, deglutition * The descriptions, with accompanying illustrations, embraced in the above chapter, were contributed, at the solicitation of the author, by Professor Norman W. Kingsley, and may, therefore, be relied upon as an authoritative exposition of the most approved manipulations and appliances involved in the practice of that difficult and important specialty of the Dental Art in which the writer excels. 681 682 MECHANICAL DENTISTRY. is not materially interfered with. The patient, having never known any other method of swallowing, is not conscious of any difficulty. Accidental lesions, however, coming generally in adult life, produce, in this respect, very great inconvenience. The remedy for these evils must be the closing of the abnor- mal passage by some means which will restore the functions to the deformed organs. In perforations of the hard palate, unless of extraordinary extent, the method is very simple. In the loss of the soft palate by disease the remedy is more diffi- cult, and in extensive congenital deformity still more compli- cated appliances will be required. As we have classified the defects, we shall also classify the appliances used for their remedy. The term obturator will be used for all appliances intended to stop a passage, as all openings in the hard or soft palate which have a complete boundary. Appliances made to supply the loss of the posterior soft palate, whether accidental or con- genital, will be called artificial vela or palates. Obturators.—Any unnatural opening from the oral cavity into the nasal cavity, which will permit the free passage of the breath, will impair articulation. Any appliance which will close such passage, and can be worn without inconvenience, will restore articulation.* Obturators were formerly made of me- tallic plate, gold or silver being most commonly employed, and many very ingenious pieces of mechanism were the result of such efforts, but latterly vulcanized rubber has almost entirely superseded the use of metals. Vulcanite has been found pref- erable to metals, being much lighter and much more easily formed and adapted, particularly when of peculiar shape. The steps to be taken in the formation of an obturator are not unlike those used in making a base for artificial teeth. It is essential that an accurate model be obtained of the opening, the adjacent palatal surface, and the teeth, if any remain in * The student will bear in mind that no cognizance is here taken of openings similar to those described in cases of congenital fissure, where the surgeon has united the soft palate, and left an opening through the hard palate, to be covered by an obturator. In such cases, neither the surgeon's operation nor the obturator will prove of any material advantage. DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 683 the jaw. For this purpose an impression in plaster is the only reliable means for such an end. Care must be used that a surplus of plaster is not forced through the opening, thus pre- venting the withdrawal of the impression by an accumulated and hardened mass larger than the opening through which it passed. To avoid this, beginners or timid operators had better take an impression in the usual manner with wax; if this is forced through, it can be easily removed, without injury to the patient. From this wax impression make a plaster model, and upon this plaster model form an impression-cup of sheet gutta-percha, with a stick, piece of wire, strip of metal, or any other convenient thing for a handle. This extemporized im- pression-cup must not impinge upon the borders of the open- ing, neither should it enter to any extent. With a uniform film of soft plaster of from one-sixteenth to one-eighth of an inch in thickness laid over this cup, a correct impression can be made without any surplus to give anxiety. Upon a correct plaster cast, taken from such an impression, make a model of the obturator out of gutta-percha, or any other plastic sub- stance, the subsequent steps being in principle the same as in making any other piece of vulcanite. It is desirable that it should enter the perforation and restore as far as possible the lost portion of the palate, but it must not protrude into or in any way obstruct the nasal passage. The entire freedom of the nasal passage is essential to the purity of articulation. That portion of the obturator which occupies the oral cavity should be made as delicate as possible, consistent with its strength and durability. A clumsy contrivance will interfere with articulation almost as much as it is improved by stopping the opening; therefore, if the obturator could be confined entirely to the opening, like a cork in a bottle, it would be all the more desirable, but as it cannot, resort must be.had to clasping to the contiguous teeth, if there are any, and if not, the obturator must spread out over the whole jaw, and receive its support in the same manner as would a set of artificial teeth. In fact, this is just what it would become in such a case, viz., an upper set of teeth bridging over 684 MECHANICAL DENTISTRY. and filling up an opening in the palate, thus combining an obturator with a set of teeth. Fig. 441 represents an obturator without teeth and without clasps, for a perforation of the hard palate, being sustained in situ by impinging upon the natural teeth with which it comes in contact. Accuracy of adaptation and delicacy in form are all that is essential in such cases, and the restoration of the speech will follow immediately. Fig. 442 represents a more complicated obturator, adapted to an opening in the soft palate. The necessity for a variation in the plan will be found in the anatomical fact of the constant muscular action of the soft palate, which would not permit, without irritation, the presence of an immovable fixture. Fig. 441. Fig. 442. This is contrived, therefore, with a joint, that will permit the part attached to the teeth to remain stationarj^, while the obturator proper is carried up or down as moved by the mus- cles. The joint, A, should occupy the position of the junction of the hard and soft palates. The joint and principal part of the appliance is made of gold, the obturator of vulcanite. The projection, B, lies like a flange upon the superior surface of the palate, and sustains it; otherwise the mobility of the joint would allow it to drop out of the opening. This flange is better seen in the side view marked C. It is readily placed in position by entering the obturator first, and carrying the clasps to the teeth subsequently. Figures 441 and 442 will illustrate the essential principles DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 685 involved in all obturators. The ingenuity of the dentist will often be taxed in their application, as the cases requiring such appliances all vary in form and magnitude. Artificial Palates.—Before proceeding to a description of appliances, a brief reference to the anatomical relations and functions of the palate will be necessary. The palate exercises quite as important an office in the articulation of the voice as does the tongue or lips. Being a muscular and movable partition to separate the nasal and oral cavities, one edge is attached to the border of the hard palate, while the other vibrates between the pharynx and the tongue. The voice, therefore, as it issues from the larynx, is directed by the palate entirely into the mouth, or through the nose, or permitted to pass both ways. A very slight deviation in this organ from its natural form will make the voice give a different sound. So will also the presence of anything that clogs the natural passages, either oral or nasal. Place any obstruction in the nasal passages, paralyze the soft palate, or let it be deficient in size, and the power of distinct articulation is wanting. The evidence of this statement is frequently found after the surgeon has successfully performed the operation of staphylor- raphy in cases of congenital fissure. In such instances (with rare exceptions) the newly-formed palate is so deficient in length, and so tense, as to be deprived of its function. It cannot be raised so as to meet the pharynx and shut off the nasal passage, but hangs like an immovable septum to divide the column of sound. Fig. 443 represents a defeetive palate belonging to the first class; the uvula and a portion of the soft palate contiguous being destroyed by disease. In such a case an obturator would be useless; the constant activity of the surrounding parts would not tolerate it. The material used for a substitute must be soft, flexible and elastic, and the elastic vulcanite is admirably adapted to this purpose. By observing the cut (Fig. 443) it will be seen that a portion of the soft palate along the median line remains, and conse- 686 MECHANICAL DENTISTRY. quently there will be considerable muscular movement which must be provided for, and which may be taken advantage of. It is desirable to make this movement available in using an artificial palate, as thereby more delicate sounds are produced than otherwise. This case presents some extraordinary difficulties, in the fact that all the teeth of the upper jaw have been extracted, and it was necessary, therefore, to adapt a plate which should not only sustain teeth for mastication, but bear the additional re- sponsibility of supporting the artificial palate. In the choice of material best adapted for the base for the teeth in such in- FiG. 443. stances, it is preferable to adopt that which will prove the most durable. There are too many interests involved to risk the adoption of anything but the best. In the case under descrip- tion, the patient desired duplicates, and two sets of teeth were made, one on gold and the other on platina with continuous gum. The plates were made like other sets of teeth, with the ex- ception of a groove located on the median line at the posterior edge to receive the attachment for the palate (marked C in Fig. 444). Fig. 444 will indicate the set of teeth with palate attached. DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 687 The wings marked letters A and B are made of soft rubber; the frame to support them is made of gold, with a joint to provide for the perpendicular motion of the natural palate, as in the case of the obturator represented in Fig. 442. When the artificial palate is in use, the joint and frame immediately contiguous lie close to the roof of the mouth; the rubber wing, letter A, bridges across the opening on the infe- rior surface or side next the tongue; the wing, letter B, bridges across the opening on the superior or nasal surface, and is also prolonged backward until it nearly touches the muscles of the pharynx when they are in repose. Both these wings reach beyond the boundary of the opening and rest on the surface of the soft palate for a distance of from one-eighth to one-quarter of an inch, thus embracing the entire Fig. 444. free edge of the soft palate. This last provision enables the natural palate to carry the artificial palate up or down, as articulation may require. When the organs of speech are in repose, there is an opening behind the palate sufficient for respiration through the nares. When these organs are in action, a slight elevation of the palate, or a contraction of the pharynx, will entirely close the nasal passage and direct all the voice through the mouth. The palate thus becomes a valve to open or close the nares, and to be tolerated must be made with thin and delicate edges which will yield upon pressure. An instrument thus made will restore, as far as is possible by mechanism, the functions of the natural organ. 688 MECHANICAL DENTISTRY'. In the case under description, the patient was a lady; the defect had existed for seven years before remedy. Articulation was very defective; distinct and perfect articulation followed within one month. Fig. 445 represents the artificial palate separated into its constituent parts. The frame is bent at the joint, in the engraving, to show a stop, marked D, which prevents the appliance from dropping out of position. Letter C shows the tongue, which enters the groove in the plate of teeth and connects them. Letters A and B are the rubber flaps, which are secured to the frame by the hooks as seen in the engraving. The process for making the rubber wings will be found described on page 693. Fig. 446 shows a more extensive palatine defect of the first Fig. 445. class. In this case the entire soft palate is gone, together with a small portion of the hard palate at the median line. Although this defect is greater in extent, the means for its remedy are more simple. The muscles of the palate are entirely gone, and consequently no perpendicular movement need be provided for. The appliance in this case will resemble an elastic obturator more than the valve-like palate of the preceding one. The principle here adopted will be substantially that recommended by Mr. Sercombe, of London, some ten years since, and consists of a plate with a set of teeth in the usual form, and attached to its posterior edge an apron of soft rubber, which shall bridge the opening on its inferior surface, extending nearly to the DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 689 pharynx. Fig. 447 represents the set of teeth with the palate attached. In Mr. Sercombe's appliance this apron was made of the common sheet rubber in the market, prepared for other uses, and is objectionable for two reasons: 1st, a want of purity in the materials of which it is compounded, in many instances substances being used in its manufacture which would prove deleterious to the health of the patient; and, 2d, its uniformity of thickness. It is far preferable, therefore, to make a mold which will produce a palate of pure and harmless materials, and which shall be of sufficient thickness in the central part, Fig. 446. and tit its anterior edge, to give it stability, and shall have a thin and delicate boundary wherever it comes in contact with movable tissue. Such a palate may be made in a mold by substantially the same process as hereinafter described. (See page 693.) It may be secured to the plate by a variety of simple means. One which will give as little trouble to the patient as any other, is to make a series of small holes along the edge of the plate and stitch it on with silk, or fine platina, gold, or silver wire may be used. It is desirable to have the plate and palate present a uniform 44 690 MECHANICAL DENTISTRY. surface on the lingual side. In fitting the plate, therefore, it may be raised along the posterior edge from the sixteenth to the tenth of an inch, according to the thickness of palate de- sired. The rubber will thus be placed on the palatine surface of the plate and present uniformity on the lingual surface. A little thought will show that in this case the patient must educate the muscles of the pharynx alone to do the work of shutting off the nares, which in the former case was per- formed by them in conjunction with the muscles of the palate. Perfection of articulation will therefore depend upon the suc- cess of the patient in this new use of these muscles. In cases of accidental lesions of the palate, such as are under Fig. 447. consideration, this education of the muscles to a new work will not be difficult. The patient at some former time has had the power of distinct articulation; his ear has recognized in his own voice the contrast between his present and former condi- tion, the ear will therefore direct and criticise the practice until the result is attained. In the case illustrated by Figs. 446 and 447, the defect had existed for twenty-eight years, the patient at the time of the introduction of the artificial palate being nearly fifty years of age. The effect upon the speech was instantaneous. Articu- lation was immediately nearly as distinct as in youth, and this DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 691 remarkable distinctness can only be accounted for upon the assumption that the pharyngeal muscles had undergone a thor- ough training in the vain effort to articulate without any palate.* The two cases chosen to illustrate the application of artificial palates in accidental lesion have required, as will have been perceived, entire upper sets of artificial teeth in connection with the palates. This selection was purposely made because the difficulties to be overcome are much greater. In cases where there are natural teeth remaining in the upper jaw, the palate and its connection with a plate would be substantially the same, and the plate might easily be secured to the teeth by clasps, in the same manner as a partial denture. Artificial Palates for Congenital Fissure.—Congenital fissure of the palate presents far greater difficulties to be overcome than cases of accidental lesion. The opening is commonly more extensive, the appliance more complicated, and the result more problematical. Nevertheless, appliances have been made in a large number of cases, which have enabled the wearer to articulate with entire distinctness, so much so as not in the least to betray the defect. The first efforts in this direction were of the character of obturators, simply plugs to close the posterior nares, and the results were far from satisfactory. It was not until it was recognized that the two classes of cases (accidental and congenital) were entirely distinct that much progress was made. Nearly every case of accidental lesion can be treated with an obturator with considerable success; very rarely will an obturator be of any benefit in congenital fissure, even if the congenital and accidental case present substantially the same form of opening. For this reason so much mystification has been thrown around these appliances within a few years past. The character of the different classes has been confounded, and an instrument admirably adapted to one class has had claimed for it an equal application to the other class. Let it be understood, therefore, as a rule to which there will be but * An account of this case appears in the Argus, of Bainbridge, Georgia, August 1st, 1868, written by the patient himself, who is the editor of that paper. 692 MECHANICAL DENTISTRY. few exceptions, that congenital fissure of the soft palate requires for its successful remedy a soft, elastic and movable appliance, and that when the most skillfully made and adapted instrument is worn, articulation must be learned, like any other accomplish- ment. Various inventions have been made for this purpose within the last twenty-five years, from the most complicated one of Mr. Stearns, described in the first edition of this work, to the extreme of simplicity of bridging the gap with a simple flap of rubber. The Stearns instrument, with all its complexity, embodied the only true principle, viz., the rendering available the muscles of the natural palate to control the movements of the artificial palate. Fig. 448. The essential requisites of an artificial palate will be to restore, as far as possible, the natural form to the defective organs with such material as shall restore their functions. Muscular power, certainly, cannot be given to a piece of mechanism, but the material and form may be such that it will yield to and be under the icontrol of the muscles sur- rounding it, and thus measurably bestow upon it the function of the organ which it represents. Fig. 448 represents a model of a fissured palate, complicated with hare-lip on the left of the mesial line. There is a division, 611�6369 DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 693 also, of the maxilla and the alveolar process, the sides being covered with mucous membrane which come in contact with each other, but are not united. The left lateral incisor and left canine tooth are not developed. Fig. 449 represents the artificial velum, as viewed from its superior surface, together with the attachment and two artificial teeth to fill the vacancy. The lettered portion of this appliance is made of elastic vul- canized rubber; its attachment to the teeth of hard vulcanized rubber, to which the velum is connected by a stout gold pin, firmly imbedded at one end in the hard rubber plate. The other end has a head, marked C, which being considerably larger than the pin, and also the corresponding hole in the velum, it is forced through,—the elasticity of the velum per- mitting,—and the two are securely connected. Fig. 449. The process, B, laps over the superior surface of the maxilla (the floor of the naris), and effectually prevents all inclination to droop. The wings, A A, reach across the pharynx, at the base of the chamber of the pharynx, behind the remnant of the natural velum. The wings, D D, rest upon the opposite or anterior surface of the soft palate. Fig. 450 represents a model, the same as Fig. 448, with the appliance, Fig. 449, in situ, The wing, D D, in Fig. 449, and the posterior end of the arti- ficial velum only in this cut being visible. Method of Making an Artificial Palate.—The success of these 694 MECHANICAL DENTISTRY. appliances depends very much upon the accuracy of the model obtained to work by. It is essential that the entire border of the fissure from the « apex to the uvula should be perfectly represented in the model, as the parts are when in repose. It is also necessary that the model show definitely the form of the cavity above, and on either side of the opening through the hard palate, being that part of the cavity which is hidden from the eye. It is desir- able, also, that the posterior surface of the remains of the soft palate be shown, but this is not essential; but it is especially important that the anterior or under surface be represented Fig. 450. with relaxed muscles and in perfect repose. The impression for such a model must be taken in plaster; it is the only ma- terial now in use adapted to the purpose. An ordinary Bri- tannia impression-cup may be used, selecting one in size and form corresponding to the general contour of the jaw. This cup will be found too short at the posterior edge to receive the soft palate, but it may be extended by the addition of a piece of sheet gutta-percha, which must be molded into such form as not to impinge upon the soft palate, but which will reach under and beyond the uvula, and thus protect the throat from DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 695 the droppings of plaster. Before using the plaster the posterior edge of the gutta-percha extension ,may be softened by heat and introduced into the mouth; contact with the soft palate will cause it to yield, so that there is no danger of its forcing away the soft tissues when the plaster is used. With the pre- caution not to use too much plaster, the first effort will be to get only the lingual surface. After trial, if the impression show definitely the entire border of the fissure, and the soft palate has not been pushed up by contact with the cup, nor pulled up by the spasmodic action of the levator muscles, it is all that is thus far desired. If, however, the soft parts have been disturbed (which on close comparison a little experience will decide), it is better to cast a model into the impression, and upon this model extemporize an impression-cup as de- scribed on page 683. This temporary cup will have the advantage of the former, insomuch that it will require but a film of plaster to accomplish the result, thus lessening the danger of disturbing the soft tissues. After the removal, if it is seen that any surplus has projected through the fissure and lapped out to the floor of the nares, it may be pared off. The next step will be to obtain, in conjunction with this impression of the under surface, which we will call the palatal impression, an impression of the upper or nasal surface of the hard palate. This can be done by filling the cavity above the roof of the mouth with soft plaster down to the border of the fissure, and while yet very soft carrying immediately the palatal impression against it, and retaining it in that position until the plaster is hard, which can easily be ascertained by the remains in the vessel from which it was taken. With the precaution to paint the surface of the palatal impression with a solution of soap, to prevent the two masses from adhering when brought in contact, there will be no difficulty in removing it from the mouth, leaving the mass which forms the nasal portion in situ- With a suitable pair of tweezers this mass is easily carried backward and withdrawn from the mouth, and the irregular surface of contact indicates its relation to its fellow when brought together. 696 MECHANICAL DENTISTRY. Fig. 451 will show such an impression. The portion marked A, B, C, will readily be distinguished as that which entered the nasal cavity. The line of separation from the palatal impression is plainly indicated in the engraving. The groove, marked D, Fig. 451. shows clearly the impression made by the delicate uvula in the soft plaster. The nasal portion is relatively large, showing an unusually large nasal cavity. Fig. 452. The vomer lies between the projections marked A A; these projections entering the nasal passages. The surfaces marked B B came in contact with the middle turbinated bones; the surface marked C in contact with the inferior turbinated bone. ^ DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 697 In many instances these turbinated bones are so large as to nearly fill the nasal passages. The method of obtaining the model of the jaw from the impression does not require any particular description. The process is similar to the making of a cast into any other mouth impression. The model represented in Fig. 448 shows a convenient form for such a cast. When the nasal portion of the impression does not indicate the superior surface of the soft palate, the part may be repre- sented in the cast by carving. It is not essential to the success of the instrument to be made that the posterior surface of the soft palate should be represented with the same accuracy that is required of the inferior surface, or of both surfaces of the hard palate. By the aid of a small mirror and a blunt probe, the thickness of the velum and the depth behind the fissure can be ascertained and the model carved accordingly. The portion of the artificial palate coming in contact with it is so elastic that it easily adapts itself to a slight inequality, rendering absolute accuracy less important. The next step will be the formation of a model or pattern of the palate. Sheet gutta-percha is preferable for this pur- pose, although wax, or many other plastic substances, might answer. The form which should be given it is better indicated by the drawings, Figs. 449 and 456, than a written description would give. The Stearns instrument, of which a cut is here given (Figs. 452, 453), was made to embrace the edges of the fissure, and was slit up through the middle, so that when the edges of the fissure approach each other, as they always do in swallowing, the two halves of the instrument would slide by each other, and a third flap or tongue was made and supported by a gold spring to cover and keep closed this central slit. This complicated provision for the contraction of the fissure is entirely superseded in Figs. 449 and 456, by making the instrument somewhat in the form of two leaves, one to lie on the inferior and the other upon the superior surface of the pal- ate, and joined together along the median line. When the 698 MECHANICAL DENTISTRY. fissure contracts, the halves of the divided uvula slide toward each other between these two leaves. The posterior portion, marked A in Fig. 449, is made very thin and delicate on all its edges, as it occupies the chamber of the pharynx, and is subject to constant muscular movement. The sides are rolled slightly upward while the posterior end is curved downward. The inferior portion marked D D, in Fig. 449, should reach only to the base of the uvula, and bridge directly across the chasm at this point, and no effort to imitate the uvula should be made. The extreme posterior end Fig. 453. should not reach the posterior wall of the pharynx when all the muscles are relaxed by a quarter of an inch, although sub- sequent use must determine whether this space be increased or diminished, thus leaving abundant room for respiration and the passage of nasal sounds. In cases where it is desirable to make the instrument independent of the teeth, as far as possi- ble, in its support, the anterior part which occupies the apex of the fissure in the hard palate may lap over on to the floor of one or both nares. Such a projection is seen in Fig. 449, 9999 DR. KINGSLEY''S ARTIFICIAL VELUM AND PALATE. 699 marked B, and a like process is seen in Fig. 456, but not let- tered. Were it not for this process in this case, the palate would drop out of the fissure into the mouth, the single clasp at the extreme anterior end not being sufficient to keep the whole appliance in place throughout its entire length. Caution must be exercised that this projection entering the nares be not too large, or it will obstruct the passage and give a disagreeable nasal tone to the voice. All these described peculiarities must be provided for in the gutta-percha model, which, after having been carefully formed to the cast, may be tried in the mouth to ascertain its length or necessary variations. When its ultimate form has been de- cided upon, provision must be made to duplicate it in soft rubber. A parallel process, and one which will be a familiar illus- tration, is used when a set of teeth is made on vulcanite base. A model or pattern form is made of gutta-percha, bearing the teeth, and in all its prominent characteristics is shaped as the completed denture is desired ; the rubber duplicate being vul- canized in a plaster mold. In like manner the rubber dupli- cate of the palate as before described may be made in a plaster mold. If plaster is used, it must be worked with much care so that the surface shall be free from air bubbles, or the rubber palate will be covered with excrescences that cannot be readily re- moved. By covering the surface of the mold with collodion or liquid silex, it will be much improved. But ordinarily plaster molds will be found too troublesome for general use. They may be put to a most excellent use, however, by using one to make a duplicate of the gutta-percha in hard rubber. This is not necessary with those who have had much expe- rience, but with beginners it will be difficult to work up the gutta-percha as nicely as may be desired; a duplicate of vul- canite will enable the operator to make a more artistic model of the palate, and one which can be handled with greater freedom. As in the course of a lifetime a considerable number of elastic palates will be required, the mold which produces them 700 , MECHANICAL DENTISTRY. should be made of some durable material. The type-metal of commerce is admirably adapted to this use. The most com- plete mold is one made of four pieces, which will produce a palate of one continuous piece. Such a mold requires very nice mechanical skill in fitting all the parts accurately, and Fig. 454. unless the operator has had experience in such a direction, it is better to simplify the matter. By making the palate in two pieces, to be joined after vulcanizing, the mold may be made in two pieces and with very little trouble. Fig. 454 shows a palate divided. Fig. 45"). Fig. 455 shows the mold or flask in which it is vulcanized. These flasks were made expressly for this purpose, but they are not so unlike the flasks in common use in dentists' laboratories that the latter will not answer. The common flask is simply unnecessarily thick or deep. DR. KINGSLEY'S ARTIFICIAL VELUM AND PALATE. 701 The mold is readily produced in the following manner: Imbed the two pieces of the palate in plaster, in one-half of the flask; when the plaster is set and trimmed into form, duplicate it in type-metal by removing the palate, varnishing the surface, molding in sand, and casting. In making the'sand Fig. 456. mold, take a ring of sheet-iron of the same diameter of the flask and three or four inches high; slip it over the flask and pack full of sand. Separate them, remove the plaster, return the flask to the sand mold, and fill with the melted metal through a hole made in the side or bottom of the flask. With one-half thus made, substantially the same process will produce the counterpart. Fig. 456 shows the palate complete with its attachment to the teeth. The palate is secured to the plate by a pin of gold passing through a hole in the palate of the same size; the head on the pin being larger than the hole is forced through, and 702 MECHANICAL DENTISTRY. . thus the two halves of the palate are bound together and joined to the plate. Fig. 457 shows a mold in four pieces. The blocks, C C, are accurately adapted to the body of the mold, marked A, and are prevented from coming improperly in contact with each other by the flanges, D D, which overlap the rest upon the sides of the main piece. B shows the top of the mold, and the groove, E, provides for the surplus rubber in packing. Such a mold makes the most perfect appliance that can be produced. The palate is one homogeneous and inseparable piece. The cut will sufficiently indicate the forms of the several parts. Each of these pieces is first made in plaster of exactly the form of which the type-metal is desired. They are Fig. 458. then molded in sand and the type-metal cast as in making an ordinary die for swaging. When in use, a clamp similar to Fig. 458 is placed around the mold to keep the several parts firm in their position. The packing of the mold with rubber will be done in the same manner as when hard rubber is used for teeth- bases; with which process it is assumed that the operator is familiar. By washing the surface of the mold with a thick solution of soap previous to packing, the palate will be more easily removed after vulcanizing. The rubber used for this purpose must be a more elastic compound than that used as a base for teeth. The composition DR. KINGSLEY''S ARTIFICIAL VELUM AND PALATE. 703 used for the elastic fabrics of commerce will answer if made of selected materials. The American Hard Rubber Company have recently placed on sale at the dental depots a compound admirably adapted to this purpose. The best results are obtained when the process of vulcanizing is carried from a heat of 230° gradually during four or five hours up to and terminating at 270°. INDEX. ADHESION, 444 ^Esthetic requirements in the se- lection and arrangement of teeth, 452 Air-chamber, manner of forming, 426 Alcohol lamps, 35 Allen's method of constructing con- tinuous-gum work, 526 Alloys, their general properties and treatment and behavior in the pro- cess of compounding, 132 gold, 91 silver, 113 platinum, 120 aluminum, 124 copper, 126 Aluminum, 122 alloys of, 124 Anatomical articulator, Bonwill's, 477 Antagonizing model for partial den- tures, 428 entire dentures, 473 upper dentures, 476 block-teeth, 504 Anthracite, 28 Antimony, 130 Appliances used in generating and ap- plying heat, 34 Application of crown and gum en- amels, 511 Articulators, 476 Artificial palates, 681 for congenital fissures, 691 Atmospheric pressure, 445 Atmospheric-pressure plates, partial, 424 modifications in the form of, 467 entire, 468 Attaching partial plates to the roots of the natural teeth, 421 Attaching teeth to a metallic base with rubber or celluloid, 662 BABBITT metal, 127 Baker's method of crowning, 234 Baking furnaces, 56 Baking porcelain teeth, 499 Bath metal, 127 Beers' method of crowning, 226 Beeswax, 146 Bell metal, 127 " Best" celluloid heater, 636 45 Bismuth, 130 Blanks, celluloid, 633 Blast crucible furnace, 71 Block-teeth, carved, 499 composition and preparation of body, 500 formulas for body, 500 composition and preparation of crown enamels, 501 formulas for crown enamels, 502 composition and preparation of gum enamels, 503 antagonizing model for entire up- per denture, 504 antagonizing model for entire up- per and lower denture, 504 forming matrix for the mold pre- paratory to carving, 506 molding, 507 carving the teeth, 510 crucing or biscuiting, 511 application of crown and gum en- amels, 511 final baking, 512 fitting and attaching to base- plate, 513 Blowpipe, oxygen, 40 oxyhydrogen, 40 mouth, 41 bellows, 45 hydrostatic, 50 Bonwill's anatomical articulator, 477 Bonwill's method of crowning, 291- 304 Brass, 126 Brass solder, 127 Bridge-work, 325 introductory remarks, 325 Dr. Webb's method, 326 Dr. Darby's method, 338 Dr. Litch's method, 339-346 Dr. Register's method, 350 Dr. Williams' method, 354-360 Dr. Low's method, 370 Dr. Dexter's method, 378 Dr. Starr's method, 383 S. S. White Dental Manufacturing Company's system of, 386 removable, 392 Britannia metal, 130 Bunsen burner, original, 37 705 706 INDEX. Burners, 37 Biittner's method of crowning, 268 CANNON metal, 127 Carved block-teeth, 499 Carving, 510 Case's method of crowning, 227 Cast metal base, 669 Celluloid base, 625 Celluloid, composition and manufac- ture of, 626 formula for, 627 processes preliminary to molding, 627 metal-faced model used in mold- ing, 629 formation of mold, 630 selection and preparation of blank, 635 molding, 635 in hot moist air, 635 in glycerine, 639 in steam, 640 in dry heat, 645-649 heaters, 636-647 "Best," 636 "New Mode," 645 repairing, 655 Celluloid facing to rubber base, 657 Chappell's method of crowning, 267 Charcoal, 25 Cheoplastic process, 669 Chinese packfong, 127 Clasps, 398 teeth suitable for the application of, 400 separation of the teeth for the re- ception of, 402 modifications in the form of, 403 plain band, 403 standard, 404 scalloped, 405 partial or stay, 406 modifications in the form of par- tial plates for the attachment of, 406 swaging plate retained by, 411 uniting the plate and, 413 vulcanite plate attached to, 610 Cleveland's air-chamber, 469 Coke, 27 Colored varnish, formula for, 184 Composition and preparation of porce- lain body, 500 Congenital defects of the palate, 681 Consideration of the principles in- volved in the application of the forces utilized as a means of attach- ment, 444 Continuous-gum work, 519 method of constructing base-plate for, 520 Land's teeth for, 525 Allen's method, 526 Hunter's method, 536 Hunter's formulas, 533 Haskell's method, 540 Field's method, 544 Tees' method, 547 Tees' formulas, 549 application of, to partial sets, 549 Converting gold alloys into required forms, 104 Coolidge's steam-gauge, 606 Crowning, root, 205 DARBY'S method of crowning, 220 Darby's method of bridge-work, 338 Defects of the palatal organs and their treatment, 681 Dentures, partial, 205 dentures, entire, 444 Dexter's method of bridge-work, 378 Dies, manner of obtaining, 188 molding, 188 dipping, 195 counter, 196 essential properties of, 198 fusible alloys used in forming, 203 Diseased mucous membranes and gums, 139 Diseased remains of teeth, 137 Draught or wind furnace, 55 Draw-plate, 111 Duplex burner, 40 Duplicating vulcanite base-plate, 622 Dutch gold, 127 EDSON'S vulcanizer, 586 Elastic force of steam at different temperatures, 600 Elements employed in refining gold, 85 Entire dentures, 444 consideration of the principles and attendant phenomena involved in the application of the forces utilized as a means of attach- ment, 444 aesthetic requirements in the se- lection and arrangement of the teeth of replacement, 452 table of temperaments, 455 the teeth as indicated by tempera- ment, 456 Entire denture attached to a swaged metallic base-plate, 465 method of constructing base-plate for upper entire dentures, 465 INDEX. 707 Entire denture, modifications in the form of base-plate for entire up- per dentures, 467 ' central cavity plates, Gilbert's, 468 Cleveland's 468 lateral cavity plates, Levett's, 468 method of constructing base-plate for entire lower denture, 471 antagonizing model for entire upper denture, 476 upper and lower dentures, 473 arranging and articulating the teeth, 482 rimming the plate, 486 constructing and attaching spiral springs, 488 investing, lining, soldering, and finishing the plate, 489 Essential properties of a die, 198 Evans' vulcanizer, 595 FELSPAR, 495 Ferrier's gas furnace, 69 Field's method of constructing contin- uous-gum work, 544 Flasks, vulcanizing, 567 Forging, 107 Formulas for porcelain body, 500 crown enamels, 501 gum enamels, 503 continuous-gum body and enamels, Hunter's, 533 Tees', 549 gold solders, 94-95 silver solder, 117 brass solder, 127 soft solder, 129 gold base-plate, 92 93 gold wire, clasps, stays, etc., 94 Babbitt metal, 127 transparent and colored varnishes, 184 articulating wax, 428 celluloid, 627 Foster's description of Moffat's method of crowning, 248 Fuels, liquid, 23 solid, 25 gaseous, 31 Furnaces, draught or wind, 55 solid fuel, 55 baking, 56 gas, Land's, 59 Rollins', 66 Ferrier's, 69 ladle, 76 Fusible alloys, formulas for, 203 table of, 203 GAS, 31 Gas crucible furnace without blast, 69 with blast, 71 Gaseous fuels, 31 Gas furnaces, 59 Gasoline, 63 Gates' method of crowning, 313 General properties of alloys, their treat- ment, etc., 132 German silver, 127 Gilbert's air-chamber, 470 Gold, geological situations of, 78 properties of, 79 influence of alloying on the prop- erties of, 80 properties of particular alloys of, 81 refining, 85 elements employed in refining, 85 separation of foreign metals from, 86 alloys of, for dental purposes, 91 required fineness for base-plate, 91 formulas for base-plate, 92 formulas for clasps, stays, etc., 93 solders, 94 reduction to lower or higher stand- ard of fineness, 96 method of ascertaining carat of any given alloy, 97 reduction of to a required carat, 97 reduction of from a lower to a higher carat, 98 table of coinage of, 99 converting alloys into required forms, 104 procuring ingot, 104 forging, 107 laminating or rolling, 107 required thickness for base-plate, 110 stays, clasps, etc., 110 solders, reduction of, into required forms, 110 wire, method of forming, 110 spiral springs, method of con- structing, 112 Gold alloy cast base, 672 Gongs, 127 Gutta-percha, 156 HAND furnace, 53 Harper's method of crowning, 233 Haskell's continuous-gum work, 540 Hawes' molding flask, 190 Hayes's vulcanizers, 58:2 Heaters, celluloid, 636 How's method of crowning, 254-261 Howell's rubber packer, 572 708 INDEX. Hunt's method of crowning, 283 Hunter's continuous-gum work, 536 formulas, 533 Hydrostatic blowpipe, 50 TLLUMINATING gas, 31 J. Impressions of the mouth, 142 Impression materials, 142 beeswax, 146 modeling composition, 156 gutta-percha, 156 plaster-of-Paris, 158 Impression cups or trays, 147 Impression in wax for partial upper dentures, 146 lower dentures, 151 entire upper dentures, 153 lower dentures, 155 gutta-percha, 156 plaster for partial upper and lower dentures, 166 entire upper dentures, 175 lower dentures, 178 India-rubber, general properties of, 553 compounding for dental purposes, 555 Influence of alloying on the properties of gold, 80 Ingot molds, 104-106 TAMES' vulcanizer, 584 KAOLIN, 496 Kerosene oil lamps, 35 Kingsley's artificial velum and palate, 681 LADLE furnace, 76 Laminating or rolling, 107 Lamps, lard oil, 34 kerosene oil, 35 alcohol, 35 Franklin safety, 36 Land's continuous-gum teeth, 525 Land's gas furnace, 64 Land's teeth for vulcanite base, 525 Lawrence's steam-gauge, 604 Lead, 128 Leech's bridge-work, 282 Litch's bridge-work, 275-346 Liquid fuels, 23 Logan's bridge-work, 319 Low's bridge-work, 370 Low's method of crowning, 242 MALLEABILITY of gold, 79 Manheim gold, 127 Manufacture of porcelain teeth, 497 Materials for impressions, 142 Matteson's method of crowning, 271 McMillen's method of crowning, 233 Metal-faced model used in molding celluloid, 629 Metallic clasps attached to rubber plates, 610 Metallie dies, 188 counter-dies, 196 Method of constructing spiral springs, 112 Modeling composition, 156 Models, plaster, 180 Modifications in the form of clasps, 403 partial plates, 406 entire upper denture, 467 lower denture, 471 Moffat's method of crowning, 248 Molding block-teeth, 507 Molding celluloid, 635 in hot moist air, 635 glycerine, 639 steam, 640 dry heat, 645 Molding flask, Hawes', 190 Molding in sand, marble-dust, etc., 188 Molds, ingot, 104-106 Morrison's method of crowning, 225 Mosaic gold, 127 Mouth blowpipe, 41 \TEW-MODE celluloid heater, 645 OBTURATORS. 682 Oil lamps, 34-35 Olefiant gas, 63 Original Bunsen burner, 37 PALLADIUM, 120 Palatal organs, defects of. 681 Partial dentures, 205 retained by clasps, 398 cylinders of wood, 418 attaching base-plate to the roots of the natural teeth, 419 by atmospheric pressure, 424 modifications in the form of plates for, 424 antagonizing model for, 428 selecting teeth for, 430 arranging teeth for, 433 antagonizing the teeth, 434 investing, adjusting stays, solder- ing and finishing, 436 vulcanite, 608 Pinchbeck, 127 Plate teeth attached to vulcanite base, 611 INDEX. 709 Platinoid metals, 120 Platinum, 118 Plaster models, 180 from an impression in wax, gutta- percha, or modeling composition for partial dentures, 180 entire dentures, 182 from an impression in plaster for partial dentures, 184 entire dentures, 186 Plaster-of-Paris, 158 Porcelain block-teeth, 499 Porcelain teeth, 494 components of, 495 silex, 495 felspar, 495 kaolin, 496 coloring materials, 496 manufacture of, 497 Preparation of root for crowning, 208 Properties of gold, 81 REDUCTION of gold to a higher or lower standard of fineness, 96 Reduction of gold solders to proper forms for use, 110 Reduction of silver to required forms for use, 116 Reese's gold alloy cast base, 672 Refining gold, 85 Register's method of bridge-work, 350 Remarks on the use of clasps, 398 Removable bridge-work, 378, 383, 392 Removal of salivary calculus, 138 Repairing celluloid base-plate, 655 Repairing vulcanite base-plate, 612 Required fineness of gold plate, 91. Rimming plate, 486 Rolling or laminating, 107 Rolling mills, 107 Rollins' gas furnace, 66 Root crowning, 205 preparation of root, 208 fitting the crown, 212 attachment with wood dowel-pins, 213 dowel-pins of wood and metal, 216 Dr. Darby's method, 220 Dr. Webb's method, 221-235 Dr. Morrison's method, 225 Dr. Beer's method, 226 Dr. Talbot's method, 226 Dr. Case's method, 227 Dr. Richardson's method, 231-288 Dr. McMillen's method, 233 Dr. Harper's method, 233 Dr. Baker's method, 234 Dr. AVeston's method, 237 Root crowning, Dr. Low's method, 242 Dr. Moffat's method, 248 Dr. How's method, 254-261 Dr. Richmond's method, 264 Dr. Chappell's method, 267 Dr. Biittner's method, 268 Dr. Matteson's method, 271 Dr. Litch's method, 275 Dr. Leech's method, 282 Dr. Hunt's method. 283 Dr. Bonwill's method, 291-304 Dr. Gates' method, 313 Dr. Logan's method, 319 Dr. Williams' method, 352 S. S. White Dental Manufactur- ing Company's Svstem, 386 Rose's fusible metal, 129 SALIVARY calculus, removal of, 138 Sand, molding, 188 Scalloped clasp, 405 Seabury's vulcanizer, 588 Separation of teeth for clasps, 402 Selecting and preparing celluloid blanks, 633 Separation of foreign metals from gold, Sheet-iron furnace, 53 Silex, 495 Silver, general properties of, 113 alloys of, 113 refining alloys of, 114 reduction of, to required forms, 116 solders, formulas for, 117 Similor, 127 Snowden and Cowman's vulcanizer, 585 Soft solder, 129 Solder, gold, 94 silver, 117 brass, 127 soft, 129 Solid fuel furnaces, 55 Solid fuels, 23 Speculum metal, 127 Spiral springs, 112 Standard clasp, 404 Starr's method of bridge-work, 383 Steam, elastic force of, at different tem- peratures, 600 Steam-gauge, Dr. Lawrence's, 604 Dr. Coolidge's, 605 Substitution of plate for rubber teeth, 611 Supports, 51 Surgical treatment of the m h after extraction of teeth, 139 710 INDEX. TABLE of fusible alloys, 203 coinage, 99 temperaments, 455 Teeth suitable for clasping, 400 The teeth as indicated by temperament, 456 Thickness of plate for clasps, 110 Time necessary to elapse after extrac- tion before inserting artificial teeth, 140 Tin, 129 Transparent varnish, formula for, 184 Treatment of the mouth preparatory to inserting artificial dentures, 136 Type-metal, 129 UNITING plate and clasps, 413 Useless and diseased remains of teeth, 137 VARNISH, transparent, 184 colored, 184 formulas for, 184 Vulcanite base-plate, 553 methods of constructing, 553 Land's teeth for, 525 flasks for, 567-571 Howell's packer, 571 vulcanizing, 573 clasps attached to, 610 plate teeth attached to, 611 repairing, 612 Vulcanite base-plate, duplicating, 622 refitting, 620 Vulcanite base-plate faced with cellu- loid, 657 Vulcanizers, 581 Hayes', 582 Whitney's, 583 James', 584 Snowden and Cowman's, 585 Edson's, 586 Woodward's, 586 Seabury's, 588 Evans', 595 Vulcanizing, 595 WAX, yellow, 146 white, 146 Webb's method of crowning, 221-235 bridge-work, 326 Weston's method of crowning, 237 White Dental Manufacturing Com- pany's system of bridge-work, 386 Whitney's vulcanizer, 583 Williams' method of bridge-work, 354- 360 Williams' method of crowning, 352 Wood dowel-pins in crowning, 216 Woodward's vulcanizer, 586 ZINC, 128 Zylonite, 661 AUGUST. 1886. 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Acetic Acid, etc. 1.75 THERAPEUTICS. Biddle. 10th Ed. - Cohen. Inhalations. Headland. Action of Med. Kirby. Selected Remedies. 2.25 Mays. Therap. Forces. 1.25 Ott. Action of Medicines. Phillips. Vegetable. Potter's Compend. Waring's Practical. THROAT AND VOICE. Cohen. Throat and Voice. .50 ----- Inhalations. - 1.25 Dobell. Winter Cough, etc. 3.50 Greenhow. Bronchitis. 1.25 Holmes. Laryngoscope. 1.00 James. Sore Throat - 1.25 Mackenzie. Throat & Nose. 6.00 ----- Larynx. - - 1.25 ----- Hay Fever. - .50 -----Pharmacopoeia. - 1.25 Potter. Defects of Speech. 1.00 TRANSACTIONS AND REPORTS. Penna. Hospital Reports. 1.25 Power and Holmes' Reports. 1.25 Trans. College of Physicians. 3.50 ----- Amer. Surg. Assoc. 4.00 TUMORS AND CANCER. Hodge. Note-book for. .50 Thompson. Of the Bladder. 1.75 Wells. Ovarian and Uterine. 7.00 -----Abdominal - - 1.50 URINE & URINARY ORGANS. Acton. Repro. Organs. 2.00 Beale. Urin. & Renal Dis. 1.75 -----Urin. Deposits. Plates. 2.00 Curling. On the Testes. 5.50 Legg. On Urine. - - .75 Marshall and Smith. Urine. 1.00 Thompson. Urinary Organs. 1.25 ----- Surg, of Urin. Organs. 1.25 -----• Calculous Dis. - 1.00 -----■ Lithotomy. - - 3.50 -----Prostate. - Paper, .75 ----- Tumors of Bladder. 1.75 —---• Stricture. - - 2.00 Tyson. Exam, of Urine. 1.50 VENEREAL DISEASES. Cooper. Syphilis. - - 3.50 Durkee. Gonorrhoea. - 3.50 Hill and Cooper's Manual. 1.00 Lewin. Syphilis. - - 1.25 VETERINARY PRACTICE. Armatage's Pocket-book of. 1.25 Tuson's Vet. Pharmacopoeia. 2.50 VISITING LISTS AND AC- COUNT BOOKS. Lindsay and Blakiston's Regular Edition. i.ooto3.oo ----- Perpetual Edition. 1.25 Watson's Led. and Cash Bk. 4.00 WATER. Fox. Water, Air, Food. Frankland. Analysis of. MacDonald. " " 4.00 1.00 2-75 WOMEN, DISEASES OF. Byford's Text-book. - 5.00 ----- Uterus. - - - 1.25 Courty. Uterus, Ovaries, etc. 6.00 Dillnberger. and Children. 1.50 Duncan. Sterility. - 2.00 Galabin. Diseases of. - 3.00 Tilt. Change of Life. - 1.25 Winckel, by Parvin. Manual of. Illustrated. ... ^.qq ANNOUNCEMENT! The Polyclinic, Vol. IV, 1886-87. The July number of The Polyclinic will commence Volume IV. The Publishers, with the co-operation of the Editor and Editorial Staff, propose to inaugurate this new volume by doubling the number of pages of reading matter, and adding a handsome cover. A change in the contents and arrange- ment will also be made. These new features will more than double the usefulness and practical value of the Journal, and as the subscription price will remain as before, One Dollar per annum, it is hoped that they will encourage many to add their names to the subscription list. To stimulate subscribers sending their names at once, the publishers offer to each a copy of Beale's Urinary and Renal Derangements. i2mo, 356 pages. 1885. See belciv. NEW FEATURES FOR VOLUME IV. THE NUMBER OF PAGES of reading matter will be doubled, making in all a volume of about 400 closely printed pages, for $1.00. A STRONG EDITORIAL STAFF and list of contributors, comprising many names well known in connection with the latest advances and discoveries made in medical science, will add their support. CLINICAL LECTURES.—Each issue will contain a number of pages of clinical material, selected from clinics held by prominent men in the various Hospitals, Colleges and Dispensatories in Philadelphia, preference being given to those that will prove of most value to the general practitioner. Dr. W. H. Morrison, a medical stenographer of large experience, has been secured to furnish these reports. A SERIES OF ARTICLES ON THE BLOOD, commencing in the July, 1886, number, by Prof. Fred. P. Henry, m.d., Physician to the Pennsylvania Hospital, etc , will form an interesting and instructive feature. Prof. Henry's purpose is to cover the subject in a systematic manner, and in this way supply what is now impossible to obtain in book form. ORIGINAL ARTICLES AND EDITORIALS from members of the Staff and other contributors, will appear in each number. THERAPEUTIC NOTES.—A section in each number will be devoted to Therapeutics. REPORTS OF SOCIETY and other meetings will appear as heretofore. But only such parts of the reports, proceedings and discussions that are of actual value and interest, will be printed. OTHER CONTENTS will consist of Translations, Selections, Book Reviews, Clinical and Miscellaneous Notes, List of new books for the month, etc. A SPECIAL FEATURE.—To each new subscriber to Volume IV who remits one dollar, in advance, we will send The Polyclinic for one year and a copy of the following book: Urinary and Renal Derangements and Calculous Disor- ders, with Hints on Diagnosis and Treatment. By Lionel S. Beale, m.d.. f.r.s., f.r.c.p., Prof, of the Principles and Practice of Medicine in King's College. London; Physician to King's College Hospital. i2mo, 356 pages 1885. Bound in strong paper covers. ***This is a new book, published in 1885, retail price $1.75, and will only be supplied in paper covers to subscribers to The Polyclinic, as above, without extra charge. Those wishing the book by itself, can obtain it from booksellers or by mail, postpaid. Cloth, $1.75. SAMPLE COPIES OF THE POLYCLINIC FREE. P. BLAKISTON, SON & CO., Publishers, Philadelphia. P. BLAKISTON, SON & CO.'S Medical and Scientific publications, No. 1012 Walnut St., Philadelphia. ABERCROMBIE. Medical Jurisprudence, for Medical and Legal Students and Practitioners. By John Abercrombie, m.d. 387 pages. Cloth, $2.50 ACTON. The Functions and Disorders of the Reproductive Organs in Child- hood, Youth, Adult Age and Advanced Life, considered in their Physiological, Social and Moral Relations. By William Acton, m.d., m.r.cs. 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Cloth, $4.00 ; Leather, S5.00 NEW CHEMICAL BOOKS. PREPARED ESPECrALLY FOR THE WANTS OF MEDICAL, DENTAL AND PHARMA- CEUTICAL STUDENTS AND PRACTITIONERS. A Text-Book of Medical Chemistry. BY E. H. BARTLEY, M.D., Associate Professor of Chemistry at the Long Island College Hospital; President of the American Society of Public Analysts ; Chief Chemist, Board of Health, of Brooklyn, N. Y., etc. Illustrated 12mo. Cloth, $2.50. This book, written especially for students and physicians, aims to be a text-book for the one and a work of reference for the other. It is practical and concise, dealing only with those parts of chemistry pertaining to medicine; no time being wasted in long descriptions of substances and theories of interest only to the advanced chemi- cal student. PART I—Treats of Light, Heat and Electricity, which are described at some length, and explanations made and applied to common phenomena. In the subject of light, only so much is given as will explain the theory and use of the spectroscope. In electricity, the principal aim has been to give such information as is needed for the proper understanding, working and care of the medical battery. PART II—Theoretical Chemistry. Only such portions of the well established principles of modern chemistry as are necessary to an understanding of the subject are given. It has been deemed best to present all these elementary parts first, that the student may be better able to study any set of isolated facts. These theories are presented in a concise, clear way, in a logical order and in a manner which the author has found specially successful in an experience of over twelve years of teaching. PART III—Treats of the natural history of the elements, of their principal compounds, with their physiological action and toxicology. PART IV—Organic bodies commonly used in medicine and pharmacy. The principal organic substances derived from animal life are given a place. In the appendix will be found analyses of the principal secretions and tissues, tables of solubilities and of specific gravities, the metric system, and other useful information. Applied Medical Chemistry. Containing a description of the apparatus and methods employed in the practice of Medical Chemistry, the Chemistry of Poisons, Physiological and Pathological Analysis, Urinary and Fecal Analysis, Sanitary Chemistry and the Examination of Medicinal Agents, Foods, etc. BY LAWRENCE WOLFF, M.D., Demonstrator of Chemistry in the Jefferson Medical College; Member of the Philadelphia College of Pharmacy and of the Chemical Section of the Franklin Institute, etc. Octavo, Cloth, $150. ***The object 01 the author of this book is to furnish the practitioner and student a reliable and simple guide for making analyses and examinations of the various medicinal agents, human excretions, secretions, etc., without elaborate apparatus or expensive processes. Practical and Analytical Chemistry. Being a complete course in Chemical Analysis, for pharmaceutical and medical students. BY HENRY TRIMBLE, Ph.G., Professor of Analytical Chemistry in the Philadelphia College of Pharmacy. Second Edition. Illustrated. 8vo. Cloth, $1.50. SUMMARY OF CONTENTS. Part I. Practical—Preparation and Properties of Gases, Preparation of Salts, etc. Part II. Section I—Bases. Group I—Potassium, Sodium, Lithium, Ammonium. Group II—Barium Strontium, Calcium, Magnesium. Group III—Manganese, Zinc, Cobalt, Nickel. Group IV—Iron, Cerium Chromium, Aluminium. Group V—Arsenic, Antimony, Tin, Gold, Platinum. Group VI—Mercury (ic) Bismuth, Copper, Cadmium. Group VII—Silver, Mercury (ous), Lead. Section II—Acids. Section Ill- Detection of Bases and Acids. Section IV—Some of the Reactions and Tests of Purity ol the more import- ant Organic Compounds Part III. Quantitative Chemical Analysis. Section I—Gravimetric Estimation Section II—Volumetric Estimation. There are also a number of useful Tables. LEFFMANN'S ORGANIC AND MEDICAL CHEMISTRY. Including Urine Analysis and the Analysis of Water and Food. By Henry I.effmann^ m.d., Demonstrator of Chemistry at Jefferson Medical College, Philadelphia! I2mo- Cloth, $1.00; Interleaved for the addition of Notes, $1.25 P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. Reissue, in an Improved Form, i2mo size, neatly bound in Flexible Cloth. Each volume sold separately. PRICE FIFTY CENTS. American Health Primers. Edited by W. W. KEEN, M.D., Fellow of the College of Physicians of Philadelphia. This Series of American Health Primers is prepared to diffuse as widely and cheaply as possible, among all classes, a knowledge of the elementary facts of Preventive Medicine, and the bearings and applications of the latest and best researches in every branch of Medical and Hygienic Science. They are intended to teach people the principles of Health, and how to take care of themselves, their children, pupils, employes, etc. Handsome Cloth Binding, 50 cents, each. Sent, postpaid, upon receipt of price, or may be obtained from any book store. HEARING, AND HOW TO KEEP IT. With Illustrations. By Chas. H. 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Wood, Jr., m.d., Clinical Professor of Nervous Diseases in the University of Pennsylvania. OUR HOMES. With Illustrations. By Henry Hartshorne, m.d., of Philadelphia, formerly Professor of Hygiene in the University of Pennsylvania. THE SKIN IN HEALTH AND DISEASE. By L. D. Bulkley, m.d., of New York, Physician to the Skin Department of the Demilt Dispensary and of the New York Hospital. SEA AIR AND SEA BATHING. By John H. Packard, m.d., of Philadelphia, Sur- geon to the Pennsylvania and to St. Joseph's Hospitals. SCHOOL AND INDUSTRIAL HYGIENE. By D. F. Lincoln, m.d., of Boston, Chairman Department of Health, American Social Science Association. "Each volume of the 'American Health Primers' The Inter-Ocean has had the pleasure to commend. In their practical teachings, learning, and sound sense, these volumes are worthy of all the compliments they have received. They teach what every man and woman should know, and yet what nine-tenths of the intelligent classes are ignorant of, or at best, have but a smattering knowledge of."—Chicago Inter-Ocean. "The series of American Health Primers deserves hearty commendation. These handbooks of practical suggestion are prepared by men whose professional competence is beyond question, and, for the most part, by those who have made the subject treated the specific study of their lives." P. BLAKISTON, SON & CO., Medical Publishers and Booksellers, 1012 WALNUT STREET, PHILADELPHIA. Holden's Manual of Anatomy. FIFTH EDITION, REVISED AND ENLARGED. 208 ILLUSTRATIONS. A MANUAL OF THE DISSECTIONS OF THE HUMAN BODY. By Luther Holden, m.d., f.r.c.s., Consulting Surgeon to St. Bartholomew's and the Foundling Hospitals, London, and John Langton, f.r.c.s., Surgeon to and Lec- turer in St. Bartholomew's Hospital. Fifth Edition. Revised and Enlarged, with many new Illustrations. Octavo. Oil Cloth Binding, £4.50 Cloth, $5.00; Leather, #6.00 *** As Holders Anatomy is the chief " Dissector " now in use, the publishers have put it in an Oil Cloth Binding. This does not retain the odors of the dissecting room, is not easily soiled, and may be washed without damage. DIAGRAM OF AXILLA (From Holden's Anatomy) 1. Axillary Artbry. a. Brachial Artery. 3. Thoracica Humeraria Artery. 4. Superior Thoracic Artery. 5. Subscapular Artery. 6. Dorsalis Scapulae Artery. 7. Posterior Circumflex Artery. Superior Profunda Artery. ,. Posterior Thoracic Nerve. 10. Long Subscapular Nerve. 11. Median Nerve. 12. Cephalic Vein. 13. Musculocutaneous Nervk. 14. Teres Major. BY THE SAME AUTHOK. HUMAN OSTEOLOGY. Comprising a description of the Bones, with Colored Delinea- Zeln t A"achmentS °f ^ M™?M- The General and Microscopical Struct',e o Bone and its Development. Carefully Revised. By the Author and A Doran f r c s with Lithographic Plates and Numerous Illustrations: Sixth Edition. 8vo Cbth £ HEtTnH'S2/c^wJp^L A*AT°MY- A Manual of Dissections. Sixth London Edi- tion. 24 Colored Plates, and nearly 300 other Illustrations. Cloth, $5.00 P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. NEW SUMGJCAL WUMKS JUST PUBLISHED. Watson on Amputations. Amputations of the Extremities and Their Complications. By B. A. Watson, a.m., m.d., Surgeon to the Jersey City Charity Hospital, to St. Francis' and to Christ's Hospital, at Jersey City, N. J.; Fellow of the American Surgical Association ; Member of the New York Pathological Society, etc. Two full-page Colored Plates, and two hundred and fifty-five Wood Engravings. Octavo. 762 -4- xix Pages. Handsomely bound in Cloth, $5.50. specimen of illustrations in watson's amputations. " This volume is an encyclopaedic monograph, containing the important facts, theories and arguments relating to amputations of the extremities, and their complications. The author's aim has been to collect facts on this subject from English, French, German and American literature. He does not lay claim to originality, but, of course, introduces, in their proper places, those observations which his own experience has led him to make on the general subject. Under the division of ' Complications,' the general subject of the treatment of wounds is discussed, with an outline of the present views on germs and germicides, for, in the words of the preface, the complications of amputation wounds are essentially the same as those which pertain to any solution of continuity involving the various tissues of the body. A great service has been done the profession by the insertion of a translation of Gaupot's and Spellmann's writings on artificial limbs. This is the fullest exposition of the subject we have yet seen in an American text-book. Too much praise cannot be given to the typographical appearance of the work. The illustrations are marvels of clearness, and do, what is not always the case, elucidate the text." —Medical Record, New York, June Both, 1885. Pye's Surgical Handicraft. A Manual of Surgical Manipulations, Minor Surgery, Bandaging, Dressing, etc., etc., for the use of General Practitioners and Students. With special chapters on Aural Surgery, Extraction of Teeth, Anaesthetics, etc. By Walter Pve, f.r.c.s., Surgeon to St. Mary's Hospital and the Victoria Hospital for Sick Children ; Examiner in Surgery at the University of Glasgow. 208 Illustrations. Octavo. Cloth, $5.00. Heath's Operative Surgery. A Course of Operative Surgery, consisting of a Series of Colored Plates, each plate containing Several Figures, Drawn from Nature by the Celebrated Anatomical Artist, M. Leveille, of Paris, Engraved on Steel under his immediate superinten- dence, with Descriptive Text of Each Operation, and numerous Wood Engravings. By Christopher Heath, f.r.c.s., Surgeon to University College Hospital, and Holme Professor of Clinical Surgery in University College, London. One Large Quarto Volume. Second Edition, Revised and Enlarged. Sold by Subscription. Full information upon application. Cloth, $12.00. P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. Practical Handbooks FOR THE PHYSICIAN and MEDICAL STUDENT. VAN HARLINGEN ON SKIN DISEASES. A Handbook of the Diag- nosis and Treatment of Skin Diseases. By Arthur Van Harlingen, m.d., Professor of Diseases of the Skin in the Philadelphia Polyclinic; Consulting Physician to the Philadelphia Dispensary for Skin Diseases, and Dermatologist to the Howard Hospital. With colored plates representing the appearance of various lesions. i2mo. Cloth, $1.7$ %* This is a complete epitome of skin diseases, arranged in alphabetical order, giving the diagnosis and treatment in a concise, practical way. Many prescriptions are given that have never been published in any text-book, and an article incorporated on Diet. The plates do not represent one or two cases, but are composed of a num- ber of figures, accurately colored, showing the appearance of various lesions, and will be found to give great aid in diagnosing. " This new handbook is essentially a small encyclopaedia. * * * Contains a very complete summary of the present state of Dermatology. * * * We heartily commend it for its brevity, clearness and evidently careful preparation."—Philadelphia Medical Times. "The author shows a proper appreciation of the wants of the general practitioner."—New York Medical Record. /™'is concisely and intelligently written, and contains many of the best formulas in use for the various forms of Skin Disease."—New York Medical Times. " This is an excellent little book, in which, for ease of reference, the more common diseases of the skin are arranged in alphabetical order, while many good prescriptions are given, together with clear and sensible direc- tions as to their proper application."—Boston Medical and Surgical Journal. "It is just the kind of book that the general practitioner will find most convenient for reference, and we feel confident that it will be appreciated."—Southern Practitioner. RINDFLEISCH'S PATHOLOGY. The Elements of Pathology. By Prof. Edward Rindfleisch, University of Wiirzburg. Authorized translation from the first German edition, by Wm. H. Mercur, m.d. (Univ. of Pa.) Revised by James Tyson, m.d., Professor of Pathology and Morbid Anatomy in the Univer- sity of Pennsylvania. i2mo. Cloth $2 00 Pl"f' £yt£nt ** h^sJ're{ace to *** American edition, says.—" A high appreciation of Prof. Rindfleisch's 7h£ n" h?.ath°l0S.IcaJ'Histology, caused me to make careful examination of these « Elements' immediatelyafter „XPi^f°r llje original. From such an exam.nation I became satisfied that the book would fill aniche »«rfc£l ™?» the student, as well as of others who may desire to familiarize themselves with general patho- logical processes, viewed from the most modern standpoint." BRUEN'S PHYSICAL DIAGNOSIS. Second Edition. A Pocket-book of Physical Diagnosis of the Heart and Lungs; for the Student and Physician. By Edward T. Bruen, Demonstrator of Clinical Medicine in the University of Pennsylvania; Lecturer on Pathology in the Women's Medical College of Phila- delphia ; 2d Edition, revised, with new original illustrations. i2mo. Cloth, $1.50 "We consider the description of the manner and rules governing the art of percussion well riven The sub VS^t^JXS&S&Jr* reqUirCS t0 ^ Wdl ^edinoTdertobeproUVunde^oo^' WOAKES ON CATARRH AND DISEASES OP THE NOSE CAUS- ING DEAFNESS. By Edward Woakes, m.d., Senior Aural Surgeon to the London Hospital for Diseases of the Throat and Chest. 29 Illustrations. i2mo. /~i_*i_ *. Cloth, $1.50 "Out of the large number of special works on catarrh, there is none for which we have such an unaualifirH ^R^'m^^*^*™*"- • * * TheUneoftreatmenrs^ete^Snal^ P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphi PRACTICAL HANDBOOKS—Continued. VON ARLT. DISEASES OF THE EYE. Including those of the Con- junctiva, Cornea, Sclerotic, and of the Iris and Ciliary Body. By Dr. Ferdi- nand Ritter von Arlt, Professor of Ophthalmology in Vienna. Translated by Lyman Ware, m.d., Surgeon to the Illinois Charitable Eye and Ear Infirmary; Ophthalmic Surgeon to the Presbyterian Hospital, and to the Protestant Orphan Asylum, Chicago. Illustrated. 8vo. 325 pages. Cloth, $2.50 " His style is condensed but clear, and his pages contain a vast amount of information, couched in such lan- guage that it will be equally instructive to the general practitioner and the specialist."—Philadelphia Medical and Surgical Reporter, May joth, 1885. TYSON ON THE URINE. A Practical Guide to the Examination of Urine. For the Use of Physicians and Students. With Colored Lithographic Plates and Numerous Illustrations Engraved on Wood. Fourth Edition. i2mo. Cloth, $1.50 " The practical man will find in this little book all that is absolutely necessary for him to know, in order to utilize fully the data supplied by the urine."—Chicago Medical Journal. GILLIAM'S ESSENTIALS OF PATHOLOGY. The Essentials of Path- ology. By D. Tod Gilliam, m.d., Professor of Physiology, Starling Medical College, Columbus, Ohio. With 47 wood engravings. i2mo. Cloth, $2.00 " The general practitioner will find in this little i2mo a convenient compendium of the current pathology of the day."—Chicago Medical Journal and Examiner. THE PRACTICAL SERIES. A NEW VOLUME JUST READY. *** The volumes of this series written by well known physicians and surgeons, oi large private and hospital experience, recognized authorities on the subjects of which they treat, will embrace the various branches of medicine and surgery. They are of a thoroughly practical character, calculated to meet the requirements of the practi- tioner, and will present the most recent methods and information in a compact shape and at a low price. Bound uniformly, in a handsome and distinctive cloth binding. DISEASES OF THE KIDNEYS, AND URINARY DERANGE- MENTS. By C. H. Ralfe, m.a., m.d., f.r.c.p., Assistant Physician to the London Hospital; late Senior Physician to the Seamen's Hospital, Greenwich. i2mo. With Illustrations. 572 pages. Just Ready. Cloth, $2.75 " The object of this volume is to present the student and practitioner with a clear, concise and systematic account of urinary pathology and therapeutics, based upon the latest ascertained facts, and supported by the best authorities. Throughout, the author has endeavored to put prominently forward the characters upon which the diagnosis of the various renal and urinary diseases is founded, and their treatment indicated."—Extract from The Pre/ace. BODILY DEFORMITIES AND THEIR TREATMENT. A Handbook of Practical Orthopaedics. By H. A. Reeves, f.r.c.s., Senior Assistant Surgeon and Teacher of Practical Surgery at the London Hospital; Surgeon to the Royal Orthopaedic Hospital, etc. i2mo. 228 Illustrations. 460 pages. Cloth, $2.25 " From what we have already said, it will be seen that Mr. Reeves has g'W_ Worthy guide for the treatment of a very extended class of cases. * * * If the other volumes of tin. A Series are as good as this, we shall be agreeably disappointed."—American Journal of Medical Science pril, l88S- " The utility of the work now before us cannot be better recommended to the appreo.. ion of the professional reading public, than by recalling that it is the first of its kind, dealing with orthopaedics from a modem stand- point."—Hospital Gazette and^Students' Journal. DENTAL SURGERY FOR GENERAL PRACTITIONERS AND STUDENTS IN MEDICINE. By Ashley W. Barrett, m.d., m.r.c.s. Eng., Surgeon-Dentist to, and Lecturer on Dental Surgery and Pathology in the Medical School of, London Hospital. i2mo. Illustrated. Cloth, $1.00 " Replete with an abundance of practical information of unquestionable utility."—Hospital Gazette and Students' Journal. P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. GOODHART AND STARR ON The Diseases of Children. A Manual for Students and Physicians. By J. F. Goodhart, m.d., Physician to the Evelina Hospital for Children; Assistant Physician to Guy's Hospital, London. American Edition, Revised and Edited by Louis Starr, m.d., Clinical Professor of Diseases of Children in the Hospital of the University of Pennsylvania, and Physician to the Children's Hospital, Philadelphia. Containing many new Prescriptions, a list of over 50 Formulae, conforming to the U. S. Pharmacopoeia, and Directions for making Artificial Human Milk, for the Artificial Digestion of Milk, etc. Just Ready. Demi-Octavo. 738 Pages. Cloth, $3.00; Leather, $4.00. The New York Medical Record, for May, 1885, says:— "As it is said of some men, so it might be said of some books, that they are 'born to greatness.' This new volume has, we believe, a mission, particularly in the hands of the younger members of the profession. In these days of prolixity in medical literature, it is refreshing to meet with an author who knows both what to say and when he has said it. The work of Dr. Goodhart (admirably conformed, by Dr. Starr, to meet American require- ments) is the nearest approach to clinical teaching without the actual presence of clinical material that we have yet seen. It does not discuss mooted questions of Pathology, but is a terse, straightforward account of the author's experience at the bedside of ailing children. Domestic hygiene is awarded its important place in the therapeutics of pediatrics. The details of management so gratefully read by the young practitioner are fully elucidated. Altogether, the book is one of as great practical working value as we have seen for many months." From the Journal of the American Medical Association, June 6th, 1885. " Nothing that concerns disease as found in childhood seems to have escaped the author's attention. From introduction to the end it is replete with valuable information, and one reads it with the feeling that Dr. Good- hart is writing of what he has seen at the bedside. It need scarcely be added that the revisions and additions by the American editor are of much value, neither too full nor too spare, and very judicious." From the Boston Medical and Surgical Journal, June 4th, 1885. " This work is written in a very agreeable style, carrying weight, from its simplicity and clearness, and the evidently large and matured experience of the author. It is especially adapted to the needs of the practicing physician rather than for the medical student, as with rare discernment it takes up important points in the details of the disease and deals with them practically, leaving the general typical course of the case to the other numerous writers who have already covered the ground in this class of cases. The type and paper are especially to be commended, and the editor, Dr. Starr, can be said to have offered a very attractive book to the medical profession." From the London Medical Times and Gazette, March 7th, 1885. "Among the great superfluity of medical books which issue from the press we are occasionally gladdened by the reading of some which not only have an unquestionable raison d' etre, but also as certainly fulfill their purpose. Such a book, we do not hesitate to say, is that which is now before us ; and, after a careful perusal, productive of both pleasure and profit, we can assure Dr. Goodhart that he owes no apology for his work, and that if, as he says, he has repeated tales that have been told before, he has repeated them with 'excellent differences.' The book cannot be abstracted. It must, and we think will, be read by all who are interested in or desire to study its subject. We feel sure, moreover, and this forcibly struck us while reading through the work, that those practitioners who have given even half the thought and study to the subject of the diseases of children that Dr. Goodhart has done, will be able to endorse the bulk of his teaching, and will recognize very many of their own unwritten, and sometimes unspoken, thoughts and beliefs; an evidence at once of the great value of the book, and an explanation of the undoubted pleasure that every expert and earnest student will inevitably experience in its perusal." xiKR WORKS ON DISEASES OF CHILDREN: DAY. DISEASES OF CHILDREN. A Practical and Systematic Treatise for Practitioners and Students. Second Edition. Rewritten and very much Enlarged. 8vo. 752 pp. Cloth, $3.00; Sheep, #4.00 MEIGS AND PEPPER ON CHILDREN. A Practical Treatise on the Dis- eases of Children. Seventh Edition, thoroughly Revised and Enlarged. Cloth, $6.00; Leather, #7.00 P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia ? QUIZ-COMPENDS ? A NEW SERIES OF PRACTICAL MANUALS FOR THE PHYSICIAN AND STUDENT. Compiled in accordance with the latest teachings of prominent lecturers and the most popular Text-books. They form a most complete set of Compends, containing information nowhere else collected in such a condensed, practical shape. The authors have had large experience as quiz masters and attaches of colleges, with exceptional opportunities for noting the most recent advances in therapeutics, methods of treatment, etc. The arrangement of the subjects, illustrations and types, are all of the most improved form, and the size of the books is such that they may be easily carried in the pocket. Bound in Cloth, each $1.00. Interleaved, for the Addition of Notes, $1.25. No. 1. Human Anatomy. Third Edi- tion. Illustrated. By Samuel O. L. Potter, m.a., m.d., late A. A. Surgeon U. S. Army. With 63 Illus. 3d Revised Ed. " To those desiring to post themselves hurriedly for examination, this little book will be useful in refreshing the memory."—New Orleans Med. and Surg. Jl. Nos. 2 and 3. Practice of Medicine. Second Edition. Especially adapted to the use of Students and Physicians. By Daniel E. Hughes, m.d., Demonstrator of Clinical Medicine in Jefferson Med. College, Phila. In two parts. Part I.—Continued, Eruptive and Periodical Fev- ers, Diseases of the Stomach, Intestines, Peritoneum, Biliary Passages, Liver, Kidneys, etc. (including Tests for Urine), General Diseases, etc. Part II.—Diseases of the Respiratory System (in- cluding Physical Diagnosis), Circulatory System and Nervous System ; Diseases of the Blood, etc. *** These little books can be regarded as a full set of notes upon the Practice of Medicine, containing the Synonyms, Definitions, Causes, Symptoms, Prognosis, Diagnosis, Treatment, etc., of each disease, and includ- ing a number of prescriptions hitherto unpublished. No. 4. Physiology, including Embry- ology. Third Edition. By Albert P. Brubaker, m.d., Prof, of Physiology, Penn'a College of Dental Surgery; Demonstrator of Physiology in Jefferson Med. College, Phila. Revised, Enlarged and Illustrated. " This is a well written little book."—London Lancet. No. 5. Obstetrics. Illustrated. Second Edition. For Physicians and Students. By Henry G. Landis, m.d., Prof, of Ob- stetrics and Diseases of Women, in Starling Medical College, Columbus. Revised Ed. New Illustrations. " We have no doubt that many students will find in it a most valuable aid."—The Amer.Jl. of Obstetrics. No. 6. Materia Medica and Therapeu- tics. Second Revised Edition. With especial Reference to the Physiological Ac- tions of Drugs. For the use of Medical, Dental and Pharmaceutical Students, and Practitioners. Based on the New Revision' (Sixth) of the U. S. Pharmacopoeia, and including many unofficinal remedies. By Samuel O. L. Potter, m.a., m.d., late A. A. Surg. U. S. Army. Revised Edition, with Index. " One of the very best we have ever seen."—Southern Clinic. No. 7. Inorganic Chemistry. New Edi- tion. By G. Mason Ward, m.d., Demon- strator of Chemistry in Jefferson Med. Col- lege, Phila. Including Table of Elements and various Analytical Tables. New Ed. " This neat pocket volume is a brief but excellent compend of inorganic chemistry and simple analysis of the metals."—Pharmaceutical Record, N. Y. No. 8. Visceral Anatomy. Illustrated. By Samuel O. L. Potter, m.a., m.d., late A. A. Surg. U. S. Army. With 40 Illus. " Worthy our recommendation to students, and a ready reference to the busy practitioner."—Chicago Med. Times. No. 9. Surgery. Second Edition. Illus- trated. Including Fractures, Wounds, Dislocations, Sprains, Amputations and other operations; Inflammation, Suppuration, Ul- cers, Syphilis, Tumors, Shock, etc. Dis- eases of the Spine, Ear, Eye, Bladder, Tes- ticles, Anus, and other Surgical Diseases. ByORViLLE Horwitz, a.m., m.d., Demon strator of Anatomy, Jefferson Medica! College. Second Edition. Revised and Enlarged. With 62 Illustrations. " Will prove very useful, both to the student and practitioner."—Valentine Mott, m.d., Ass't to the Prof, of Surgery, Bellevue Hospital, New York. No. 10. Organic Chemistry. Including Medical Chemistry, Urine Analysis, and the Analysis of Water and Food, etc. By Henrv Leffmann, m.d., Demonstrator of Chemis- try in Jef^jj^usaTtnistvCoUege; Prof, of Chemistry in>*Pract^ollege of Denta! Surgery- Philadelpff£(j-/ " It is a «eful and valuable addition to the series 01 Quiz-Compends."—College and Clinical Record. No. n. Pharmacy. Based upon "Rem- ington's Text-Book of Pharmacy." By F. E. Stewart, m.d., ph.g., Quiz-Master at Philadelphia College of Pharmacy. Bound in Cloth, each $1.00. Interleaved, for the Addition of Notes, $1.23. • These books are constantly revised to keep up with the latest teachings and discoveries. P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. FOR 1887. The Physician's Visiting List. (LINDSAY & BLAKISTON'S.) PUBLISHED ANNUALLY; NOW LN LTS THIRTY-SIXTH YEAR. CONTENTS. CALENDAR FOR 1887 and 1888. 1 LIST OF NEW REMEDIES. Prepared by Sam'l TABLE OF SIGNS ^. L- P°TTER> MD- MARSHALL HALL'S READY METHOD IN j SYLVESTER'SI METHOD FOR ARTIFICIAL ASPHYXIA RESPIRATION. Illustrated. POISONS AND ANTIDOTES. | DIAGRAM OF THE CHEST. A DESCRIPTION OF THE METRIC OR FRENCH ^DECIMAL SYSTEM OF WEIGHTS BLANK LEAVES, for Visiting List. " " " Monthly Memoranda. AND MEASURES. DOSE TABLE, rewritten in accordance with the new (sixth) Revision of the U. S. Pharmacopoeia. DISINFECTANTS AND DISINFECTING. EXAMINATION OF URINE, prepared by Dr. Judson Daland, based upon Prof. Jas. Tyson's "Handbook for Practical Examination of Urine." LIST OF STANDARD REFERENCE BOOKS. INCOMPATIBILITY. A NEW COMPLETE TABLE FOR CALCU- LATING THE PERIOD OF UTERO-GESTA- TION. Addresses of Patients and others. Addresses of Nurses, their references, etc. Accounts asked for. Memoranda of Wants. Obstetric and Vaccination En- gagements. Record of Births and Deaths. Cash Account, etc. NEW FEATURES.—A glance at the above contents will show several new features that have been suggested by our experience, or by those who have used the Visiting List for many years, as being practical and useful. These additions have been made, however, without increasing the size of the book and without altering its character or general arrangement in any way. SIZES AND PRICES. For 25 Patients weekly. Tucks, pockets and Pencil, $1.00 50 " " " " " 1.25 75 " " " " 1.50 100 " " " " " 2.00 5° << ~ \t ^ f Jan. to June ) ,, ,, ,, „ .„ 2Vols- 1 July to Dec. j 2-5° 100 « » 2 Vols. j|TrJnn 1 ...... 3-oo ( July to Dec. J J INTERLEAVED EDITION. For 25 Patients weekly. Interleaved, tucks and Pencil, 1.25 50 " " " " " 1.50 .< .. ^ T7- i f Jan. to June ) ,, ,( 5° 2Vols- {July to Dec.} 3-oo PERPETUAL EDITION, without Dates. S^'Can be commenced at any'timet and used until full. Similar in style, con- tents and arrangement to the regular edition. No. 1. Containing space for over 1300 names, with blank page opposite each Visiting List page. Bound in Red Leather cover, with Pocket and Pencil, $1.25 No. 2. Containing space for 2600 names, with blank page opposite each Visiting List ' ^/ nd like No. 1, with Pocket and Pencil, . . . . 1.50 '" These lists, v \ dates, are particularly useful to young physicians unable to estimate the numt -/of patient they may have during the first years of Practice, and to physicians in localities where* epidemics occur frequently. " For completeness, compactness, and simplicity of arrangement it is excelled Dv norle ;n the market "—N. Y Medical R tcord. y " The book is convenient in form, not too bulky, and in every respect the very best Visiting List published."— Canada Itedtcad and Surgical fournal. " After all the trials made, there are none superior to it."—Gaillard's Medical Journal. ^ It has become Standard."—Southern Clinic. ", ^:e.2ular as the seasons comes this old favorite."—Michigan Medical News. << ^ruS qulte convenient for the pocket, and possesses every desirable quality."—Medical Herald. .. w um°St P°Pular Visiting List extant."—Buffalo Medical and Surgical Journal: We have used it for years, and do not hesitate to pronounce it equal, if not superior, to any."—Southern Clinic. " This Visiting List is too well known to require either description or commendation from us."—Cincinnati Medical News. P. BLAKISTON, SON & CO., Publishers, 1012 Walnut Street, Philadelphia. Holden's Anatomy. Fifth Edition. 208 Illustrations. In Oil-cloth Binding, $4.50. A Manual of Dissection of the Human Body. By Luther Holden, m.d., f.r.c.s., Eng. Fifth Edition, re- vised and enlarged, and witji* new illustrations. Edited by John Langton, m.d., Surgeon to, and Lecturer on Anatomy at, St. Bartholomew's Hospital, London, etc.; with 208 illustrations. 8vo. Oil-cloth Binding, $4.50; Cloth, $5.00 ; Leather, $6.00. " *#* This edition of Holden's Anatomy is eminently a Student's book, without as well as within. As a text-book it has become so well known that it is unnecessary to speak of its contents. The printing and binding of this new edition, however, should be explained. It has been printed on very handsome paper, so that the minutiae of each wood cut is clearly brought out; and the student will meet with no difficulty in tracing each muscle, nerve, artery, vein or organ in the illustrations. Many of the cuts have the explanations printed on them; a very great advantage, enabling the reference to be made quickly, and fixing the fact more surely. Marginal references have been inserted throughout the text, to catch the eye, at each important paragraph. The binding has been put on so that the book will LAY OPEN AT ANY page. It being used so largely in the dissection room suggested to the publishers the binding of it in Oil-cloth. The advan tages of this binding are, that it will not retain the odors of the dissecting table, does not soil easily, it may be washed without damage, and while quite as durable, allows of our making a lower price for the book than in either cloth or leather binding. It is, therefore, particularly well suited for the dissecting room, operating table or students' use generally. May be ordered through any bookseller, or from the publishers. P. BLAKISTON, SON & CO., Medical Booksellers, 1012 WALNUT STREET, PHILADELPHIA. HOLDEN'S ANATOMY. Octavo. 208 Illustrations. Cloth, $5.00; Leather, $6.00. IN OIL-CLOTH BINDING, $4.50. A Fifth Edition. Revised, Enlarged and with new Illustrations. Orbicularis oris . Pterygo-maxil- \ lary ligamentj Glosso-pharyngeal n. ----- Stylo-pharyngeus. Mylo-hyoideus . Os hyoides . . Thyro-hyoid ) ligament j Pomum Adami . Cricoid cartilage Trachea . . . Superior laryngeal n. and a. External laryngeal n. Crico-thyroideus. Inferior laryngeal n. CEsophagus. Fig. 15. Holden's Anatomy. Muscles of the Pharynx. This is eminently a student's book. Its great popularity as a dis- sector suggested to the Publishers binding it in Oil-Cloth. The ad- vantages of this binding are that it does not soil easily, does not retain odors; it may be washed, and while quite as durable, and as handsome in appearance as either cloth or leather, it admits of its be- ing sold at a lower price. This edition has been very carefully printed and bound, and lays open flat at any page. P. BLAKISTON, SON & CO., 1012 Walnut St., Philadelphia. * NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICO 3NOIQ3W jo Aavaan tvnouvn 3NiDia3w jo Aava8ii national library of medicine national library of MEDICINE 3NI3I03W jo Aavaan tvnouvn 3NOia3w jo Aavaan ivnouvn 3NIDI03W jo Aava c > NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY 3Nma3w jo Aavaan tvnouvn snidiosw jo Aavaan tvnouvn NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY < 3NiDi03w jo Aavaan tvnouvn snidiqsw jo Aavaan tvnouvn 3NIDI03W jo Aavat NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE •a NATIONAL LIBRARY C 3NOIQ3W jo Aavaan tvnouvn snqiosw jo Aavaan tvnouvn 3NIDI03W jo Aavas NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY OF MEDICINE NATIONAL LIBRARY < y\ NLM041427368