The distinguishing factor of dental training and one which is not required to the same de gree in any other department of the healing art is the manual skill and mechanical train ing needed for the successful practice of the prosthetic or restorative operations which the dentist is constantly called upon to perform. It was the lack of facilities in medical schools for obtaining the necessary training in the me chanical procedures of dental art that led to the establishment of the first dental college and placed dental education upon a basis independent of general medical education. The increase in knowledge of the diseases of the mouth and its contained organs and the growing recognition of the vital relationships of the oral tissues to the body as a whole, have gradually com pelled the broadening of the dental educational curriculum until at present all of the funda mental medical sciences are included in the cur ricula of the best dental colleges, and upon this scientific foundation is erected the superstruc ture of technical education and manual train ing necessary to the art of the dentist. The development of dentistry in America has been phenomenal especially in all that pertains to its art side. The incorporation of the systematic teaching of mechanical dentistry in the college course instead of depending upon the uncertain educational results of the apprenticeship system has had greatly to do with creating a body of American practitioners skilled in their art. It is in fact for his skill as an operative dentist that the American practitioner has been mainly dis tinguished. The art of replacing lost portions of tooth crowns by gold fillings has had its greatest development in America; indeed as we know the operation to-day it may be said to have originated there. As originally practised the ideal gold filling was one which simply acted as a stopper inserted in a cavity produced by decay, for the purpose of excluding moisture and furnishing a surface sufficiently resistant to withstand the wear and tear of mastica tion. The filling was finished on a level with the cavity margins and no attempt was made to restore the lost contour of the tooth in imi tation of its natural configuration. When, how ever, the discovery of the cohesive property of annealed gold foil was made and promulgated by Dr. Robert Arthur, of Baltimore, in 1855, the whole method of filling teeth with gold was revolutionized and complete artistic restoration of the normal configuration of the tooth by building with gold foil became the accepted ideal of practice. In connection with the general use of cohesive gold as a filling material certain in genious and important devices came into exist ence as adjuncts to the operation of tooth filling, having their origin in the necessities of the case. These were the dental engine, the mallet and the rubber coffer-dam. The opera tion of preparing the cavity for the reception of the gold involves the removal of decayed por tions and frail margins, and giving to the cavity a retentive shape, so that the filling when in serted shall be solidly and immovably held in place. The early methods of cavity preparation were laboriously performed by small chisels and cutting instruments manipulated exclusively by the hand. Hand instruments were also exclu sively used for the insertion and condensation of the gold foil in building the filling and sub sequently giving it the required form and sur face finish. The introduction of the dental en gine run by foot-power or by electric motor has not only greatly facilitated the operation of tooth-filling but has made possible more accu rate and perfect results. So manifold has been the improvements made in the dental engine and its equipment of accessory appliances that it may, if the operator so desire, be used for every step of the operation from cavity preparation to the finished filling. As the cohe sive property of gold, upon which its value in restoring the form of the tooth depends, is at once destroyed by contact with moisture, great difficulty was formerly experienced during large filling operations in excluding the gold from contact with saliva; napkins, bibulous paper and various mechanical devices were used for the purpose, but were often insufficient to prevent the destruction of a filling during the progress of its insertion. The device known as the rub ber darn, introduced by Dr. S. C. Barnum of New York, about 1865, solved the problem of effectually excluding moisture from the teeth undergoing filling operation, and made possible more extensive and thorough restorations than had previously been attempted. The discovery of the usefulness of the cohesive property of gold in filling operations soon brought into requisition other means than simply hand pressure or condensing the gold foil into a solid homogeneous mass. It was soon found that greater solidity could be obtained by the per cussive force of a mallet applied to the gold through the plugging instrument, so that the use of the mallet became general for the pur pose, largely through the persistent advocacy of Dr. W. H. Atkinson of New York. The earlier forms of condensing mallets were simply hand mallets with heads made of various materials and different weights to attain desired varia tions in the impact and quality of the blow de livered upon the condensing instrument. Later, automatic mallets, combining a plugging instru ment and mallet, were introduced. In these instruments the blow was produced by a ham mer propelled by the release of a spring com pressed by pressure, the malleting mechanism being contained in a casting connected with the plugging point which was applied to the surface of the filling upon which the impact of the blow was ultimately expended. In 1867 Dr. W. G. A. Bonwill of Philadelphia introduced his electro magnetic mallet, an instrument which involved the principle of the Morse telegraphic recorder so modified that the armature of the electro magnet was effectively utilized as a mallet act ing upon the free end of the gold-plugging in strument. With the automatic interrupter of the current afterward added to it the Bonwill instrument contributed greatly to the improve ment of gold-filling operations both in the solidity of the gold, its more accurate adapta tion to the walls of the cavity and in lessening the fatigue and discomfort of both patient and operator incident to the operation. The blows delivered by the electromagnetic mallet while light are extremely rapid, an advantage which its inventor sought to realize in a later device, to be used in connection with the dental engine, known as the Bonwill engine mallet, an instru ment of high efficiency and the parent device of many subsequent modifications. To further lessen the stress encountered alike by patient and operator in the malleting of gold fillings the cast gold inlay was introduced by Dr. W. H. Taggart in 1905. This method of restoring lost tooth substance consists in the utilization of a contoured gold plug obtained by casting pure gold into a mold made from a wax pattern and which is set into the prepared tooth cavity with a thin layer of cement. The extensive use of gold as a filling material as the perfection to which the technique of its use for that purpose has been developed, especially in America, has recently brought about a reactive tendency against the display of elaborate operations of gold, especially in conspicuous positions in the front teeth, esthetic considerations stimulating the search for some substitute more in harmony with the texture and color of human teeth. Recently through the invention of an improved technique by Dr. C. H. Land of Detroit, Mich., and the further investigations of Dr. N. S. Jenkins, an American dentist formerly residing in Dresden, Germany, the use of porcelain as a restorative material has become practically pos sible and bids fair to supplant gold as a filling at least in conspicuous situations. The dura bility of porcelain restorations as compared with gold fillings remains to be tested by time and experience, but the immediate result is in all respects in favor of porcelain, especially in the matter of appearance, which so harmonizes with the teeth structure in color and texture as to be invisible when the operation is correctly per formed. The filling of cavities is also exten sively done with plastic materials that have the property of becoming hard in the course of time after having been inserted in a soft state. This class of materials includes the amalgams and cements, also gutta-percha. Certain of these materials, the cements for example, serve only a temporary purpose, and their usefulness is therefore of limited duration. Silicate cements which at present are extensively employed as substitutes of gold and porcelain in the restora tion of decayed portions of the anterior teeth must also be classified as limited in duration.
The amalgams, however, while unsightly in ap pearance, are extremely useful ; being quite durable and capable of insertion without great difficulty, they can be used in cases of great loss of tooth structure, thus restoring many cases that could not otherwise be as successfully treated and with less cost than gold filling. Following the researches of Koch in bacterial pathology the role played by micro-organisms in the causation of dental diseases became the subject of study by numerous investigators, notably the late Prof. W. D. Miller, an Ameri can dentist resident in Berlin, through whose researches the cause of tooth decay was ex plained. Similarly the causal relation of disease producing micro-organisms to disorder of the dental pulp and the tissues surrounding the roots of teeth has been clearly made out, with the result that operations upon the pulp chambers and root canals of teeth in which the pulp has been devi talized by disease or design are now among the recognized conservative operations of dentistry.
This advance in the treatment of pulpless teeth has made possible the permanent saving of mul titudes of teeth in a condition of comfort and functional usefulness which were previously in evitably sacrificed or lost. Later investigations in the domain of dental and oral pathology are throwing light upon the causes and improving the modes of treatment of those diseases of the retaining tissues of the teeth which when un checked result in their early loss by destruction of their attachment to the gums and alveolar sockets. The grafting of artificial crowns of porcelain upon healthy natural roots is accom plished in a large variety of ways, the attach ment being by metallic dowels cemented into the properly enlarged pulp canal of the root, this being in most cases reinforced by means of a gold collar or ferrule connected with the porce lain crown, closely encircling the periphery of the root at and slightly under themargin. Perfect adaptation of the crown end is obtained by correctly shaping the exposed por tion of the root and then the properly fitted porcelain crown is attached to this foundation by gold solder and backing plate of gold con necting with the platinum pins of the crown. In certain cases hollow crowns, made entirely of gold plate shaped to the contour of the original natural crown, are used upon the roots of the grinding teeth instead of porcelain crowns, as they possess the advantage of superior dura bility. Aggregations of crown permanently united upon their contiguous surfaces and sup porting crowns in spaces where teeth have been extracted constitute so-called bridge work. No restorative operation in dentistry requires more judgment and skill, nor has any dental pro cedure been more abused in its performance than bridge work. Where the operation is in telligently and skilfully done, it constitutes the most satisfactory result both as to comfort, utility and appearance that prosthetic dentistry has yet attained; otherwise it defeats the very object for which only it should be undertaken, namely, the restoration of the denture to full functional usefulness and esthetic appearance.
The department of dentistry technically known as mechanical pr prosthetic dentistry comprises all those operations and the labora tory manipulation of the materials involved in the construction of substitutes for lost dental organs and parts of the oral tissues. Where lost teeth are to be replaced by means other than those described as crown and bridge work, it is done by mounting the porcelain crowns upon a base-plate adapted to the surface of the palatal vault as well. An impression of the alveolar arch is taken in an impression tray containing a plastic material which will subsequently harden, usually plaster of Paris or a modeling compound consisting of gum kauri, stearin and talc ; bees wax or beeswax and gutta-percha have been used, but are now practically abandoned for this purpose. Into the matrix formed by the im pression a batter of plaster of Paris is poured, which after it has hardened forms the cast upon which the base-plate to support the artificial teeth in the mouth is constructed. The base plate may be of vulcanite or of metal, and in the former case the porcelain teeth are adjusted to the cast by means of wax, and a wax plate is constructed which is the counterpart of the pro jected finished vulcanite plate. When the ar rangement of the teeth to the wax trial plate has been found to be satisfactory by actual trial in the mouth of the patient, it is returned to the cast and the whole embedded in plaster of Paris contained in a sectional iron founder. The upper and lower sections of the flask are sepa rated after the investing plaster of Paris has fully hardened, and the wax is completely re moved by a stream of boiling water, leaving a facsimile matrix in the plaster, which is then packed full of vulcanizable caoutchouc; the flask is then closed and after being firmly bolted together is subjected to the action of the heat from superheated steam for about an hour at 320° F. in a vulcanizer. The case is allowed to cool and when removed from the matrix the now thoroughly hardened plate is finished with a fine polish and is ready for insertion in the mouth. Metallic plates serving as the base of support of artificial teeth are constructed by stamping or swaging the flat plate cut approxi mately to the desired pattern between male and female dies, made from zinc and lead, respec tively, which have been obtained by casting the molten zinc into a sand matrix made from the plaster of Paris model of the alveolar arches. This furnishes a zinc model or male die upon which a female die or counter-die of lead is cast, and between these the metallic base-plate is struck up to the form of the alveolar arch upon which it is intended to rest. Upon this base plate porcelain teeth are fitted and attached by a metallic connection between the platinum pins (which for the purpose are baked in the porce lain texture of the artificial teeth) and the base plate, union being made by soldering. Dentures upon an enameled platinum base-plate consti tutes a form of work known as continuous gum work, in which, after the teeth by means of their pins have been united to the plate by soldering with pure gold, porcelain paste or as it is technically called, is packed around the roots and between the teeth; then carved into form until the natural contour is reproduced. The piece is then subjected to high heat in a muffle until vitrified, after the man ner of firing or baking china or pottery. It is next given a coating of enamel in imitation of the natural gum color, and after this has been fused in the muffle and the piece finally finished it constitutes the most artistic, hygienic and anatomically perfect denture of which dental art is capable. The prosthetic department includes, besides the restoration of lost teeth, the con struction of mechanism for the correction of palatal defects whereby imperfect speech and deglutition are restored to practically normal conditions; it includes also the construction of splints in the treatment of fractures of the jaws and the restoration of parts of the jaws lost by accident or disease; construction of mechanism for the correction of irregular positions of the teeth and for the restoration of facial deformi ties due to irregular or imperfect development of the jaws and bones of the nasal or facial regions. The correction of irregularities in the position of the teeth has developed such im portance and covers such a wide field of study and work as to constitute a distinct specialty of modern dental practice. This department of dentistry is termed orthodontics; its importance is due not only to the cosmetic value of its results, but because of the direct bearing which irregular positions of the teeth and deformities of the dental arches exert upon the bodily health. The whole field of dental and oral pathology has been so far developed by study and research as to place modern dental practice distinctly among the recognized specialties of the healing art. Most of the bacteria causing general bodily disease find access to the system through the mouth, which is also the habitat of many bacteria, benign and disease-produc ing as well. Hence the hygienic care of the mouth as a protection against disease invasion is of the utmost importance. Late researches have shown that the mouth, its tissues and its secretions, and the teeth themselves, furnish important indications of certain bodily diseases, malnutrition, etc., which are extremely valu able as diagnostic means. The training of the dental practitioner has therefore been enlarged so that in the foundation elements it is now co-• extensive with that of the practitioner of gen eral medicine, but specialized with reference to its particular field of inquiry.