The American text-book of prosthetic dentistry : in contributions by eminent authorities

Front matter

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Preface

If the Editor interprets correctly the prevailing opinion of the dental profession as reflected in the utterances of many teachers, the issue of an extended and strictly modern text-book upon the Principles and Practice of Prosthetic Dentistry will answer a need of the times. During the past thirty years the practice of prosthesis has undergone a transformation parallel with that of operative dentistry during the same period. Plans, operations, and methods which, despite the retrospective asseverations of many, were but crude and indefinite, have received a development which has widened this branch of dental practice and greatly increased its utility.

There is contained in the body of the present volume the material which a consensus of opinion declares the best that dental prosthetic art has evolved. It is designed to answer the purposes of a text-book for the under-graduate student, a clear and thorough laboratory manual, and a work of reference for the dental practitioner.

In conformity with these plans, the central object is the exposition of principles and the teaching of their practical application. No eifort has been spared by Editor and collaborators to survey, arrange, and classify the mass of data gleaned from the literature of the past fifty years and from the practice of those who have raised prosthetic dentistry to its present plane.

In arranging this vast accumulation of material so that one case might be correctly placed as representative of a class, matters which are not directly pertinent to the subject of laboratory technology are deliberately excluded from these pages, it being confidently believed that a mastery of the technique and materials presented will give the student a command of the subject throughout its many ramifications. The means employed to this end are lucidity of description and such a wealth of illustration as to render the text as clear as words and pictures can make it. Particularly in the matter of engravings the publishers have been more than liberal, desiring that the book should, above all, fill the gap complained of by teachers — the want of a complete and modern text-book from which obsolete and useless material should be expunged.

10 PREFACE.

It is a prominent purpose of the work to sift from the multitudes of devices and operations which have been advanced, those which have so stood the test of time as to receive the endorsement of continued application by the most skilled and experienced prosthetists, and to describe in detail those principles which are applicable to the greatest number of cases. From the beginning of dental journalism the pages of periodicals have teemed with processes conceived and advanced with the avowed purpose of time-saving. A careful examination and test of such methods has exhibited one strikingly common feature — namely, that economy of time, when made the main purpose, is generally effected at the expense of accuracy. The demand for precision is quite as imperative in dental prosthesis as in any other art, and it is evident, therefore, that the saving of time should be made a subordinate motive. These observations apply with peculiar force to the department of artificial crowns and bridge-work. The past twenty-five years have created in these subjects alone a literature embracing sufficient material to make a volume much larger than this. Such literature has been carefully examined, and is here reduced from its many ramifications into basal principles and their embodiments, wdiich will be found to include all those devices which have merited and found actual and continued clinical use.

Prosthetic Dentistry, it is almost needless to state, is more than a mere mechanical art, for, contrary to the nature of such arts, there are but few entirely constant rules upon wdiich its practice may be based. Rarely is any operation in this art an exact repetition of a preceding one, the resemblance which one case bears to another being more often remote than close. The taste, experience, and judgment required for the proper practice of prosthetic dentistry place it in near kinship with one of the fine arts.

Full credit for sources of information has been accorded by the contributors in their several chapters. In addition to these, the Editor tenders his grateful thanks for favors and courtesies extended by Prof. S. H. Guilford, Dr. John N. Farrar, Dr. Eugene S. Talbot, Prof." E. H. Angle, Dr. Norman W. Kingsley, Prof. E. C. Kirk, and especially to Prof. H. H. Burchard for assistance rendered in the editorial w'ork and in the revision of proofs ; also to Dr. N. S. Essig for his valuable assistance in the preparation and revision of illustrations.

Acknowledgment of obligation and thanks are due and proiFered to the S. S. White Dental Manufacturing Co. ; the Buffalo Dental Manufacturing Co. ; the Wilmington Dental Manufacturing Co. ; and to

Messrs. Johnson & Lund.

CHAKLES J. ESSIG.

Philadelphia, August, 1896.

LIST OF CONTRIBUTORS.

HENKY H. BURCHAED, M. D., D. D. S.,

Special Lecturer on Dental Pathology and Therapeutics, Philadelphia Dental College, Philadelphia.

CHAELES J. ESSIG, M. D., D. D.S.,

Professor of Mechanical Dentistry and Metallurgy, Department of Dentistry, University of Pennsylvania, Philadelphia.

W. W. EVANS, D. D. S., Washington, D. C.

C. L. GODDARD, A. M., D. D. S.,

Professor of Orthodontia, College of Dentistry, University of California, San Francisco.

GEANT MOLYNEAUX, D. D. S.,

Professor of Prosthetic Dentistry and Metallurgy, Ohio College of Dental Surgery, Cincinnati.

RODEIGUES OTTOLENGUI, M. D. S., New York, Editor of the " Items of Interest."

AMBLEE TEES, Jr., D. D. S.,

Lecturer on the Continuous-gum Method, Department of Dentistry, University of Pennsylvania, Philadelphia.

ALTON HOWAED THOMPSON, D. D. S.,

Professor of Dental Anatomy, Kansas City Dental College, Kansas City, Mo.

By Rodrigues Ottolengui, M. D. S.

PROSTHETIC DENTISTRY.

Chapter I The Mechanical Laboratory, Its Equipment And Arrangement

By Chaeles J. Essig, M. D., D. D. S.

It is highly important that the furniture and equipment of a dental laboratory should be neat, appropriate, and adapted especially to the comfort of the workman and to cleanliness and celerity in his manipulations. In order to correct the want of uniformity in methods and results which is a noticeable feature of the average dental laboratory operations, students should in the very beginning be taught to be systematic in the care of tools and instruments, as well as in all the manipulative stages of their work. They should be required to find suitable places for every article which enters into laboratory work, so that when not in use tools and apparatus should be returned to the places assigned them.

The usual equipment of a dental laboratory consists in a suitable work-bench carefully adapted to the purposes for which it is to be used ; a moulding-box ; plaster-table and sink ; a swaging-block and anvil ; at least two lathes, one designed especially for the grinding and fitting of teeth, the other for finishing and polishing only ; a mechanical blowpipe table, supplied with gas-burner on the Bunsen principle, of sufficient capacity to allow of the soldering of full dentures.

In addition to these permanent articles of laboratory furniture it will be necessary to provide a suitable furnace for the melting of zinc, lead, and alloys commonly used in making dies and counter-dies, and also another and different one to be used for the occasional melting of gold and silver and in the formation of alloys to be used as solders.

The accessories of soldering, moulding rings and flasks, ingot-moulds, rolling-mills, draw-plates, pickling solutions, with the most suitable vessels for holding the same, grinding and polishing materials, fluxes, varnishes, adhesive wax, and bench tools, all necessarily form part of the equipment of the dental laboratory, and will each be separately described in these pages.

The ivork-bench should be constructed of cherry, ash, or well-seasoned oak : it should be provided with not less than two sets of drawers, as

2 17

THE MECHANICAL LABORATORY.

shown in the diagram, the two lower ones (Fig. 1, A) being reserved for the reception respectively of gold and silver scraps and filings, while the upper drawers (Fig. 1, B) will be found convenient for the reception of the ordinary bench tools, such as pliers, shears, plate-punches and cutters, horn mallet, etc. The drawers (A) should be 20 inches long by 15 inches wide, inclusive, and should consist of a frame of cherry or oak 2 inches wide by 1 inch thick and a tray (C) of tin or zinc 1 inch in depth. By this means the workman is provided with a spacious tray Avhich he

Fig. 1.

draws out to cover his lap in a manner to catch the filings and cuttings of the precious metals while he works.

The height of the work-bench should be about 34 inches, and in length, when designed for the convenience of two workmen, about 5 feet 6 inches ; the width may be 24 inches. The top should be 2 inches in thickness, and immediately over the tool-drawers (B) should be arranged a rest for convenience in filing and finishing. These rests are usually made of the same hard wood as the top of the bench, 2 inches wide and about 3 inches long, tapering from 1^ inches in thickness where it is mortised into the table to ^ an inch at its extremity. (See Fig. 1, D.)

Accessories of the Worh-hench. — A good vise is an important adjunct to the work-bench, and is indispensable wdien the draw-plate is used for reducing the size of gold, platinum, or silver wdre.

Rubber slabs of \ an inch in thickness by 6 inches square afford excellent rests, not only for the protection of the top of the bench from injury by contact with dies and counter-dies in the preliminary stage of plate-making, but also as pliant and elastic rests for the metallic or rubber denture during stoning and finishing.

Moulding-box. — This article of laboratory furniture, shown by Fig. 2, demands special attention in its construction, otherwise it will prove a constant annoyance, as no ordinary wooden box will remain tight enough to prevent the moulding sand from falling through its seams upon the floor. The diagram shows the general design of one which has been found practical and convenient. It is 4 feet long, 26 inches wide, and 36 inches high. It is lined icifh sheet zinc, which does not rust by contact with the moist sand, and eifectually prevents the escape of the latter. It is provided with a shelf (A), upon which each completed mould may be placed while others are being prepared or until ready for the casting. It has two drawers (B), 18 inches Avide by 4 inches deep, in which may be kept either plaster or the smaller moulding-flasks, rings, and other acces-

MOULDING-BOX AND ACCESSORIES.

'sories of the moulding operation. It is provided with a lid, and should be kept closed when not in use, so as to exclude all foreign substances which might seriously interfere with casting.

Accessories of the moulding-box consist of the various sizes of the " Bailv moulding-flask," which, with the method of using them, will be described under the head of dies and counter-dies ; one Hawes flask (see page 313) and two or three sections of galvanized iron stove-piping, each having the dimensions of about 6 inches in length by 41 inches in diameter. This simple form of flask is very desirable for many moulding operations of the dental laboratory, its value consisting in the fact that it will accommodate all si2;es of models, and that it is less liable, on account of the greater quantity of moulding sand required by it, to the "bubbling"

Fig. 2.

which often occurs when melted zinc is poured in contact with the scant and tightly-packed sand in the " Baily flask."

It is essential that all moulding operations should be performed upon perfectly level surfaces, and for this purpose two or three " mouldingblocks" of seasoned pine, 8 inches square by 2 inches thick, will be found convenient aids. In order to avoid lumpiness and to secure uniformity of condition in the sand when moistening it preparatory to moulding, a sieve of not less than 12 inches in diameter, with meshes of a minimum size of Jg- of an inch, will be found of value. The sieve should be formed of brass or copper wire, as an ordinary iron-wire sieve will soon become useless from oxidation, which is greatly assisted by contact with the wet moulding sand. A painter's brush, 1^ inches in diameter by 2 inches in length, will be found useful and convenient for the purpose of removing adherent particles of moulding sand from the surface and interstices of the plaster model each time it is drawn from the sand matrix.

Anvil and Swaging-block. — As the laboratory is often situated on an upper floor, the use of the hammer in swaging plates may be the cause of much annoyance from noise and vibration. This, however, can be entirely avoided by interposing rubber between the block and the floor upon which it rests. Fig. 3, A, shows the block of pine or poplar

THE MECHANICAL LABORATORY.

wood, 7-|- inches square by 23^ inches high. B and C represent a sheet of rubber 8|^ inches square by 1 ^ inches thick, securely fastened to the lower end of the block by screws. This block fits into a box made of 1^- inch pine boards, broader below than above (Fig. 4j D), furnished with a loose bottom, made of 2-inch seasoned oak or ash, and provided with four pieces of solid rubber cylinder (Fig. 3, F) 1^ inches in diameter by 2 inches

Fig. 3.

Fig. 4.

Fig. 5.

long, let into it by holes of the same dimensions bored to a depth of 1|- inches. Two thicknesses of rubber are thus interposed between the block upon which the anvil rests and the floor of the laboratory, and so much of the sound due to the percussive force of the hammer is thereby deadened that scarcely any noise or vibration will be observed by persons in other parts of the house.

The anvil (Fig. 5), which should weigh not less than 40 pounds, may be securely fastened to the block upon which it rests by strong iron

staples (G), and the box or outside covering of the block reinforced by iron bands, as shown in H. A swaging block so constructed may be looked upon as a permanent piece of laboratory furniture, and one that will not be likely to get out of order. Two swaging hammers are required — one, weighing about 2 pounds, is of much use in starting the plate. The heavier one, which should weigh 5|^ or 6 pounds, is used with greater force after the plate has been made to partially conform to the zinc die when there is no longer danger of its pleating or folding.

Plaster-table and Sink (Fig. 6). — The working of plaster, which forms so important a part of the operations of the dental laboratory, is entitled to much more care and attention than it usually receives at the hands of the mechanical dentist. It may be employed with neatness and precision, when its results become truly artistic, or, as is too often the case, it may be handled in so slovenly and untidy a manner as to greatly lower the

PLASTER-TABLE AND ACCESSORIES.

standard of results, and, unless kept carefully within the precincts assigned it, cause the laboratory to become a most unattractive place. It is of importance, therefore, that a suitable table be provided upon which the casting and subsequent trimming of plaster models and other parts of the laboratory work depending upon the employment of plaster may be performed. The plaster-table should also be supplied with a sink and receptacle for the cuttings and refuse fragments. The accompanying diagram shows such a table and sink which the author has found to be practical and convenient. It has been designed especially to protect the floor and other parts of the laboratory from contact with plaster. It is 31 inches high, 23 inches wide, and 27 inches long, and has an opening (A) 8 inches by 8 inches square, under which rests a

Fig. 6.

Fig. 7.

portable box (C), 12 by 12 inches square, intended to receive all cuttings and refuse plaster.

The table is provided with a small rest (B) for convenience in resting the model while trimming to proper dimensions. It is also provided with a drawer for the reception of plaster knives, spatulas, and camel'shair brushes used in mixing plaster and in casting and trimming models.

The accessories of the plaster-table, named in the order in which they are used, consist, first, of two short broad-necked bottles, for sandarac and shellac varnish, two or more flexible rubber plaster bowls, the same number of bone, ivory, or steel spatulas for mixing, one or more " plaster knives," such as are sold at the dental depots for the purpose of reducing the size of plaster models, or a bench-knife, as shown in Figs. 7, 8, will be found very effective in cutting down hard plaster in preparing the model for flasking in rubber or celluloid work, and a number of different sizes of camel's-hair brushes, which are indispensable in carrying the plaster into the deeper parts when running or casting impressions for partial dentures, and indeed all impressions having deep and more or less inaccessible points, which might not be perfectly reached by the gravitation of the plaster unassisted by some such means as is suggested by the use of the camel's-hair pencils or brushes.

Two kinds of varnish are usually employed in the preparation of the surfaces of impressions for running out the models^ so as to prevent too close adhesion of one to the other. One is transparent and dries upon the plaster without color. The other is of the color of burnt sienna, and imparts a dark-yellow stain to the plaster. The first is made by dissolving 5 ounces of gum sandarac in a quart of alcohol. The latter is formed of gum shellac and alcohol in the same proportions. Gum sandarac dissolves rather slowly, and requires a good quality of alcohol free from a very considerable percentage of water ; otherwise it will have a milky appearance and will not afford a perfectly glazed surface when applied to the plaster impression. These two varnishes are employed for totally different purposes. In running out an impression the object should be to obtain a perfect surface to the model, one that is free from air-bells or roughness of any kind, as such imperfections will be represented on rubber or celluloid dentures by multitudes of minute globules which are highly irritating to the mucous membrane of the mouth. The shellac varnish should be applied first, as it penetrates the plaster and discolors it sufficiently to serve as a guide in removing impressions from models, and thus prevents the workman from injuring the teeth or prominent parts of the model. After the shellac varnish has been allowed to dry the sandarac should be applied with a camel's-hair brush until the surface is glazed. It should be laid on of a uniform thickness, but not in such quantity as to fill up deep places or to injure the correctness of the fac-simile of the mouth.

After the last coat of varnish has been allowed to dry, if the glazing of the surface is satisfactory, the plaster impression merely requires to be dipped in water to ensure saturation and to further harden the varnish, when it is ready for running the model. Careful attention to these details will produce a model possessing hardness of surface and with the glazed appearance which is noticed when plaster is poured and allowed to set upon glass. This result, however, cannot be obtained when oil or solutions of soap have been used : such substances should never be applied to plaster impressions, as they do not afford surfaces sufficiently smooth or hard upon which to form rubber or celluloid dentures. To get the best results in the handling of plaster, the latter in mixing should be slowly dropped into water until it becomes saturated and settles to the bottom of the bowl, so as to expel the air. The surplus of water is then poured off and the plaster well stirred, when it should be carried to the surface of the impression and into the deep parts with a camel's-hair brush, and the balance built up with the spatula.

Plaster of Paris (calcium sulphate, CaSOJ is prepared from a native calcium sulphate, containing two molecules of w^ater of crystallization (CaSOi+ 2H2O), called gypsum when found in opaque masses, alabaster when it presents a semi-opaque appearance, and selenite when it occurs in transparent prisms. The first is the common source of plaster of Paris. It is prepared by heating the mineral in an oven where the heat does not exceed 127° C. (261° F.), by which the water of crystallization is expelled. It is afterward reduced to a fine powder, and when mixed with water it solidifies after a short time from the re-formation of the same hydrate ; but this effect does not happen if the gypsum has been overheated and its affinity for water destroyed. In setting there is always a slight evolution of heat and more or less expansion.

For dental purposes there should be two kinds of plaster provided.

THE CARE OF METALS. 23

For taking impression of the mouth, a finely-ground plaster is required, which sets quickly, but does not become hard enough to demand a very considerable exhibition of force in its fracture, which is nearly always unavoidable in removing impressions of mouths containing natural teeth and perhaps several dovetailed interdental spaces.

A different quality of plaster is demanded for running models and in vulcanite and celluloid work, which need not necessarily possess the quick-setting property, but in which greater hardness and strength are indispensable requirements. (See page 298.) Plaster when not being used should be kept covered to shield it from occasional dampness of the atmosphere and to protect it from water and foreign substances which might accidentally fall into it. The tin cans in which plaster is furnished by the dental depots are admirably suited for this purpose, and no improvement over them need be looked for.

Care of Metals used in the Formation of Dies and Counter-dies. — Zinc and lead are the metals most frequently employed for this purpose, but there are also several alloys which have found favor with some of our most skilful and experienced mechanical dentists. The composition, fusing-points, and physical properties of all of these will be described in another chapter. There are other alloys used in crown- and bridge-work, and these demand special care in their storage and handling. First, it is important that they be kept strictly apart and that separate melting-pots or ladles be provided for each. This is especially true with regard to zinc and lead, two metals which resemble each other so closely that it may easily happen that a zinc die be remelted in a pot already partly full of lead. The necessity for carefully keeping these two metals separate in all moulding operations will readily be appreciated when it is remembered that zinc and lead combine with each other to a very limited extent, and that when melted together and allowed to cool they separate in two layers, the upper, and consequently the lighter one, zinc, retaining 1.2 per cent, of the lead, while the lower layer consists of lead alloyed with 1.6 per cent, of zinc. If by accident lead becomes mixed with zinc used for dies, the lead by its greater specific gravity settles to the bottom and fills up the deeper portions of the sand matrix representing the alveolar ridge, the most prominent part of the die. This may not be discovered until an attempt to swage is made, when the die will be found to be totally unfit for the purpose. In such cases the mixed metal should be discarded and new zinc substituted. Lead belongs to a small class of metals which are so soft that they can be scratched by the finger-nail, while zinc is so much harder that no impression can be made upon it by that means. This simple test is therefore an excellent way of deciding between lead and zinc as they appear in the pot or ladle after having been previously melted.

In casting metals of the class to which zinc and lead belong their fusing-point should be borne in mind, so that they may not be subjected to temperatures greatly in excess of that which is sufficient to melt them; otherwise partial oxidation will occur, which greatly impairs the working qualities of the metals by rendering them viscid and difficult to pour when fused, and so brittle after casting as to be unfit to bear the blows of the swaging hammer without breaking.

While the metals used in the formation of dies and counter-dies are

THE MECHANICAL LABORATORY.

melting they should be watched, and, when the last solid portion becomes fluid, removed from the furnace and allowed to stand for a few moments until the fused metals are observed to crystallize at the edges, when they are in the proper condition for casting ; for when zinc or lead are poured at a temperature greatly in excess of their fusing-points the shrinkage of the die is not only greater, but the amount of vapor generated by contact with the moist moulding sand is very likely to cause " bubbling," which is nearly always fatal to the die.

The Precious Metals. — Scraps and filings of the precious metals, such as gold, platinum, and silver, shoidd be kept free from contamination with particles of zinc, lead, or tin, which metals are constantly being used about the work-bench, while at the same time admixture with each must be avoided. Small pieces of pattern tin or fragments cut from dies and counter-dies, when overlooked and melted with either gold, silver, or platinum, reduce their fusing-points, lessen or destroy ductility and malleability, and greatly modify color. With the utmost care it is almost impossible to maintain the standard of these metals, and a remelting of scraps and filings of gold taken from the drawer of the workbench will always be found to be below the grade of the plate from which they were cut : this is partly due to impurities such as have been referred to, fragments of steel from the files used, and the solder employed in the construction of the plate, more or less of which invariably finds its way into the gold drawer in reducing the plate to its proper dimensions. When it becomes necessary to remelt scraps for the construction of backings, for instance, filings should be excluded altogether, and only clean scraps, free from solder, should be selected.

Modes of Melting Metals. — The means employed for this purpose will depend upon the character of the metal or alloy to be fused. The fusing-point of such alloys as are used for dies and counter-dies in crown- and bridge- work, which melt at temperatures ranging from 1 58° F. to 236° F. — and there are no less than six of these alloys now in use — may be accomplished by simply placing a sample of any one of them in a small iron ladle provided with a suitable handle, and holding it over a gas-jet or the flame of an alcohol or oil lamp, or, in the case of zinc,

lead, or Babbitt's metal, in an ordinary stove Fig. 9. or furnace, or, better still, when gas is avail-

able, by one of the gas-furnaces devised by Mr. Fletcher of Warrington, England, for melting zinc and lead for dies and counter-dies and for the fusion of all alloys which may be melted in an iron ladle at or below red heat.

MODES OF MELTING METAL.

Figs. 9 and 10 show an improved form of furnace with ladle for melting zinc, lead, and other metals for dies and counter-dies, which is believed to be a better furnace for that purpose than any other yet made. It works equally well with any gas-supply available ; the speed of working is, however, proportionate to the supply of gas. The burner can be removed from the casing and used for other purposes if desired.

When gas is not available, the gasoline furnaces used by plumbers for melting solder have no superiors in point of convenience and rapidity, while the cost of the fuel is very slight. Fig. 11 gives an illustration of this furnace. The lower portion is a galvanized reservoir which holds the gasoline. In the top of the reservoir Is a stopcock with a short rubber tube attached, through which air is forcibly blown for a moment until pressure is made upon the surface of the gasoline, which forces it out through a tube continuous with the supply-tube of the burner reaching from the bottom of the tank, and conveys it to the burner, the supply to which is regulated by a valve. The burner is so constructed that the flame from the burning jet of gasoline is projected upon a recurved portion of the supply-tube, which is heated thereby to a temperature sufficient to vaporize the gasoline before it makes its exit at the jet. The result is a large volume of gasoline vapor under high pressure, burning with an intensely hot flame, without any disagreeable odor, and with more than ample heating power for the requirements of the case. When once started the action is perfectly automatic. The cast-iron shell around the burner directs the heat toward the sides of the melting-ladle, which stands within it and upon a support immediately above the flame. A gauze packing in the exit-tube interposed between the burner and the gasoline reservoir prevents any danger of ignition of the fluid in the latter while the furnace is in action. The form of this furnace, made by C. Gefrorer, Philadelphia, is admirably adapted for use with the Baily melting-pots commonly used in the dental laboratory.