1902 Encyclopedia > Dentistry

Dentistry




DENTISTRY. The province of dentistry embraces the art of treating diseases and lesions of teeth, and supplying artificial substitutes in the place of these organs when lost. Disease of the teeth is not always a mere local affection, but may, and very generally does, arise from constitutional causes. With cases of the latter description the dentist, unless qualified as a surgeon or physician, is not in a posi-tion to deal, except in so far as to repair or ameliorate the local affections produced. The morbid conditions of the system leading in some way to disorders of the dental tissues are.various and dissimilar in their nature; and the exact connection between such morbid conditions and their effects upon the teeth is not well understood. In this way the diagnosis, the treatment, and the removal of the cause might be considered more properly the duty of the general practitioner than of the specialist. Up to a very recent date this has been more particularly the case, dentists until lately having in the greater number of instances been educated with a view to proficiency in the mechanical rather than the surgical department of their profession; while what surgical knowledge they, in a few cases, did acquire was confined to certain facts connected exclusively with the organs upon which they were expected to operate. From the Lancet for 3d June 1876 it appears that not much more than fifty of all the numerous body of so-called surgeon-dentists of the United Kingdom then pos-sessed in reality any medical or surgical diploma at all.

A special examination in dentistry now exists in connec-tion with the Eoyal College of Surgeons of England for students training in that profession, a certain amount of in-formation being required in various branches of medicine and surgery. A curriculum of study in these departments has been arranged; and candidates who can produce certificates of attendance on it are admitted for examination, and, if found fit, receive a certificate entitling them to practise as dentists.

In America this special system has for long been adopted and carried to a much greater extent. Colleges of dentistry are established in many of the leading cities there, each with what they designate a faculty of professors in the various departments of the art. In the Denial Cosmos, vol. xvii. No. 11, an American periodical, advertisements appear of seven different dental colleges, with seventy-eight professors, demonstrators, &c. The professorships in these institutions comprehend those of mechanical dentistry, operative dentistry, dental physiology, dental pathology, dental therapeutics, mechanical dentistry and metallurgy, institutes of dentistry, &c. In each a diploma in dentistry —" doctor of dental surgery," or of " dental medicine," as the case may be—is conferred, the general fee for which seems to be $30, on the candidates having fulfilled the curriculum and passed the examination.

In the medical schools and examining boards in Scotland all this is different. No special or partial diploma is there given by the Eoyal College of Surgeons or other licensing body, while diseases of the teeth and adjacent structures are understood to be made subjects of lecture and examina-tion in the same manner as other regional or special diseases occurring in the practice of medicine or surgery ; and great as the improvements certainly are which such arrangements as those of England and America are on the old system, still it is to be hoped, and it is likely, that ere long practitioners devoting themselves to dental surgery will—like oculists, or aurists, or obstetricians, or other physicians or surgeons restricting themselves to or selecting one branch of practice in preference to another— be at the same time fully qualified medical men.

Number of Teeth. —The complement of teeth in the adult human subject amounts to 32—16 in the upper, and 16 in the lower jaw. These are divided into what are termed in-cisors, canines, bicuspids or small grinders, and molars or the large grinding teeth. The order in which these different forms of teeth are placed in each jaw is the following:—_ there are four incisors in front; immediately behind these on each side is placed the canine or eye tooth; next come the bicuspids, two on each side; and behind these again are placed on each side the three molar teeth, the last of which is sometimes termed the wisdom tooth, from its gene-rally appearing so late as from eighteen to twenty-five and in this way to he subordinate to fully qualified practitioners ; and 3d, those who advocated dentists being altogether dissociated from surgeons, and having a college and a diploma of their own. The old tendency, however, of desiring to appear a kind of surgeons here again soemed to predominate, as the idea of the dental college and diploma was abandoned for the prospect of being attached in some way or other to the Eoyal College of Surgeons of England. The difficulties then presented, however, were not few, and many of them are found still to exist. A full medical or surgical education was always deemed desirable by those best able to judge of it, but the obstacle had been the mechanical acquirements which dentistry required and which would have to be added to a surgeon's qualifica-tions, an arrangement entailing a very protracted period of education. The scheme of partial surgical instruction, again, did not give the title to registration as qualified practitioners, and both schemes were held to entail considerable hardships on provincial candidates owing to the prescribed classes and constituted examining board being exclusively confined to London. All these representations were, however, set aside and in 1858 the dental certificate of the College of Surgeons of England noticed above was establishsd.

In the infant or milk teeth, or, as they are more pro-perly denominated, the temporary teeth, the number and class of these organs is different. Here only 20 members of the series exist, and are divided into four incisors, two canines, and four molar teeth, similarly placed—ten in each jaw. The four temporary molar teeth represent or rather precede the four bicuspid teeth of the adult set, while the six molars above and below of the adult are not repre-sented in the temporary set at all. In other words, the true permanent molar teeth have no predecessors.

Dentition.—The temporary set appear, or are cut, as follows. The two lower central incisors appear between the sixth and eighth months of infant life—these are generally succeeded in a few weeks by those of the upper jaw; the two lateral incisors of the upper jaw next appear about the eighth or ninth month, and those of the lower jaw quickly follow ; the anterior molars of the lower jaw are cut about the twelfth, fourteenth, or sixteenth month, and those of the upper jaw immediately after ; the canines appear about the seventeenth or eighteenth month, generally those in the upper jaw first; and before the age of two and a half years the second milk molars have usually commenced to appear, thus completing the temporary set of teeth at the age of about three years.

The temporary set of teeth begin to be shed between the sixth and eighth years of life. Previous to this, however, the first permanent molars are cut, generally about the age of seven. These are followed by the central and then by the lateral incisors. Next come the anterior bicuspids about nine years old; the posterior about ten or eleven ; the canines about twelve ; the second molars at thirteen ; and the last molars, or wisdom teeth, from the eighteenth to the twenty-fifth years of life. Deviations from the order and time of appearance of both sets occur, but the above may be regarded as the general rule in the evolution of the temporary and permanent teeth of the human subject.

Structure and Form of Teeth.—The structure of both sets may be said to be the same. The body of each tooth is composed of a dense bony substance termed dentine. This is invested on the crown by a cap of still more dense material termed enamel; while the root, or fang, is coated externally by a layer of a softer substance, closely resemb-ling ordinary bone, and termed cement. In the centre of each fang, and extending into the body of the tooth, is a hollow canal termed the pulp cavity, for the passage of vessels and nerves.
In form the incisors of both jaws are single-fanged, as are also the canines. The bicuspids of the lower jaw are also single-fanged, while those of the upper jaw are occa-sionally double-fanged, or have a single fang bifid at its extremity. The lower molars, both temporary and per-manent, possess two fangs, one behind the other. These two fangs are widely separated in the temporary molars; while, on the other hand, in the posterior molars of the permanent set they are not uncommonly united into one. The upper molars of both sets possess three fangs—two external or cheek fangs placed one behind the other, and a third situated on that side of the tooth next the palate.

No such spaces exist between any of the teeth in the dental arch of man as occur in the lower animals. In this way, where the jaw is small, or where unusually rapid or simultaneous appearance of the members of the second, or persistence of those of the first set occurs, irregularity of the teeth results. This is sometimes increased by the evolution of supernumerary teeth, these being generally out of the line of the others; and occasionally matters are rendered worse by the natural teeth being themselves of unusually large size. Cases also occur in which the number of the teeth is defective, and some rare instances have been recorded where these organs never appeared at all.

The remedy in cases of dental irregularity is to remove by extraction such teeth as are in the way, and by mechanical contrivances, known as regulating plates, to apply pressure in such a manner as will move the misplaced tooth or teeth into their normal position, and retain them there for some time afterwards. Such plates are constructed on the same principles, and of the same materials, as the bases of artificial sets, which will come to be treated of afterwards. It not unfrequently happens that nature, if left to herself, effects a wonderful improvement in cases of dental irregularity. This is frequently observable where it is the upper canines which are misplaced. These teeth when appearing, as they often do, outside and much above the necks of the adjoining teeth, occupy a long time in descending, and in certain cases the anterior portion of the maxillary arch seems to enlarge sufficiently to afford space for their almost perfect arrangement during this period. The same thing occurs, but to a less marked extent, in the case of other teeth; in general, however, nature requires to be assisted by art in some way, as has been above indi-cated, where the irregularity exists to any great amount.

Diseases of Teeth.—The teeth being living organisms are, like other structures in the animal body, subject to disease. Some of the diseases bear a close resemblance to mere chemical decomposition, such as occurs in dead or inorganic matter, and at a certain stage of some dental affections a pro-cess of the kind does no doubt occur ; but this is so mixed up with, and accompanied and preceded by vital action, that to consider it as a mere chemical or physical lesion would be pathologically incorrect. Various arguments have been advanced by its advocates in support of the chemical theory of dental caries ; but however ingenious or specious these at first sight appear, they fail to explain many phenomena in the origin, the period of occurrence, and the stages and progress of this disease, unless the vital element in its nature be also taken into account.

Dental caries, or decay of the teeth, may briefly be described as consisting in a previous imperfect development, or in the access of some morbid action interfering with the nutrition or vitality of their tissues, thus rendering them liable to any destructive agencies to which they may be subjected, by which they become disorganized, disintegrated, and broken down, leaving the sensitive pulp exposed, whereby acute pain is occasioned, especially when the destruction of the protective tooth substance has been rapid. Sometimes the process of decay is insidious and unobserved. Its advent is then supposed to have been sudden, and its progress more speedy than has really been the case. This, however, in many instances arises from the condition of matters being overlooked until the enamel, which resists destruction longest, being undermined and falling in, reveals for the first time the cavity existing underneath. Pain, probably also for the first time, is then experienced from exposure and irritation of the dentinal pulp, and toothache, as it is termed, is produced.

Necrosis, or death of a whole tooth, is another lesion to which these organs are liable. This may result from either acute or chronic inflammation in the tissues connecting them with the jaw, or from a blow, or from any other cause leading to their vascular supply being cut off. The necrosis may involve the whole tooth, or it may be partial —as, for example, where it is limited to one fang of a multiple fanged tooth. In these cases there may be no breaking down of texture, but the tooth becomes discoloured, loosened, extruded, and at last detached from its socket, from which after a time, and generally after considerable uneasiness, it drops out.

Exostosis, or a morbidly increased growth of certain parts of a tooth, being in almost every instance confined to the cement substance described as covering the fang or root, is an affection somewhat obscure in its outward symptoms. It is generally a consequence of previous disease of the tooth, leading to chronic inflammation of the textures covering the fang and lining the socket (or alveolus) in which it is implanted. This leads to a deposi-tion of new material in the cement till that substance appears in nodular masses attached to or surrounding the-apex of each fang, and sometimes uniting several of such fangs into one. The presence of this additional and in-creasing bulk of hard tissue within the inclosing socket produces pain of a severe and somewhat anomalous charac-ter by pressure on the adjacent nerves, which is often mis-taken for neuralgia or tic of a less unaccountable origin. It further acts within the unyielding bony socket referred, to as a means of rendering removal of the tooth much more difficult, owing to the bulbous extremity of the enlarged fang acting like a rivet in its fixation. Generally, however, the teeth in which exostosis occurs have been too long the subjects of irritation and decay not to be suspected when obscure pain of a less localized nature exists in their vicinity; and not unfrequently there is found round the necks of teeth or stumps so affected a red and tumified con-dition of the gum, sufficiently indicative of the state of matters below to warrant their extraction.

Alveolar abscess, or gum boil, as it is popularly denominated, is a localized inflammation going on to suppuration, and generally confined to the tissues surrounding the apex of a tooth fang. The pain usually commences with a feel-ing of tenderness and enlargement or lengthening of the whole tooth. The gum becomes swollen and tender over the whole depth of the root, generally to a greater extent on the outer side of the jaw. The face also becomes swollen, and the glands in the neighbourhood of the jaw feel enlarged and tender. The pain is not commonly con-tinuous, but rather remitting in its character, sometimes ceasing altogether—only, however, to be followed by an in-creased attack, while its repeated exacerbations night and day lead in many cases to very considerable constitutional disturbance. After a time the purulent matter secreted makes its way to the surface, sometimes finding an escape alongside of or through the pulp cavity of the fang, and very frequently, as the name given to the disease indicates, by pointing and discharging itself through the gum.

Occasionally, instead of pointing on the surface of the gum, the matter takes a more indirect course and points on the surface of the cheek, bursting and leaving an open sore there which seldom closes until the tooth or stump has been extracted. At an early stage of this disease fomenta-tions and other modes of relieving inflammatory action do good, but evacuating the matter by means of incisions or extraction of the offending tooth are the only reliable remedies at a later period.

Teething.—What is termed dentition, although in its widest sense properly including the development of the teeth within, as well as their subsequent appearance through, the superimposed tissues, is generally restricted in ita application to the latter division of this process, more especially as it occurs in connection with the temporary or milk set, during the period of early infancy. The genesis, increment,,and evolution of these organs involve so-much of what is purely physiological, and would entail the discussion of so many points of a histological nature, that only the latter stages of evolution or cutting of the teeth can be referred to here. Eegarding this occurrence, the most vague and contradictory opinions have been entertained. Erroneous notions of its nature, and of the exact manner in which to account for many of its phenomena, have been and still are promulgated. A number of morbid affections incident during infancy are set down as clearly attributable to the tooth's penetration of its inclosing tissues, and considered by many authorities as of every day occurrence; while the views advanced with reference to the pathology and treatment of such cases, suppositional or otherwise, are equally various and conflicting. The pro-bable solution of the difficulty seems to be that, while evil consequences may in certain instances be traceable to dentition, the frequency and importance of such cases is very much exaggerated.

Extraction.—-This constitutes the most important opera-tion of a surgical nature falling under the care of the dentist, and is chiefly called for where the condition of the tooth, from disease or injury, precludes the possibility of saving it by stopping or other means. The operation is also frequently resorted to where the teeth are too crowded in the jaw, or where they are irremediably misplaced, or where super-numerary members of the series exist and occasion incon-venience. In order to extract any tooth successfully, there is demanded a knowledge of what its configuration normally ought to be, and of the proper instrument to use ; and, along with these, the condition to which decay or other disease may have reduced the tooth must be kept in mind while proceeding with the operation.

In seizing a tooth in order to its extraction the part upon which the hold is taken should be sufficiently sound and strong to withstand the force necessary for dislodging the fangs; and to obtain such a hold it is necessary to thrust the grasp of the instrument as far as possible beyond the spot affected by decay. It should then be detached from the walls of its socket in that direction where least resistance is likely to be met. This must be judged of according to circumstances, but in general is indicated by an acquaintance with the anatomy of the structures concerned. After being thus loosened it has merely to be lifted from the jaw to complete the operation. Sometimes a tooth is so firmly secured in the jaw that its own tissue will give way before it will separate from the alveolar cavity in which it is fixed. This is particularly the case in friable teeth; and frequently even in the strongest teeth the root or fangs may be malformed or bent, or secured in such a manner as renders their extrac-tion extremely difficult or altogether impossible by any ordinary means.

The instruments employed in extraction may be divided into those which grasp the tooth between their blades and literally extract or draw it out, such as forceps, and those which apply the dislodging force by acting as a lever in the manner of a crow bar, such instruments being termed elevators. The key, an instrument of great power, but now very properly almost disused, partakes in a measure of the properties of both these instruments, but that in a very imperfect and disadvantageous manner. In some rare cases, however, it may be found of much service when used with circumspection. It is impossible here to enter into detail regarding the different forms of forceps, elevators, and other instruments required in dental surgery; but one great principle may be laid down with respect to all of them, which applies especially to forceps, and that is that their form should be as simple as possible consistently with fitting and grasping securely the particular tooth they are intended to remove, and with conveniently reaching that part of the mouth in which it is situated.

Regulation of Teeth.—In the extraction of teeth for the purpose of affording space in cases of dental irregularity from overcrowding, it often becomes necessary to remove a healthy organ, and before doing so among the permanent teeth certain questions present themselves for consideration. Unless there be a fair probability of such a step being sue cessful it endangers the loss of two teeth should the originally misplaced one be so objectionable and so unyield-ing to treatment as to require this. In the temporary set the principal disadvantage connected with the removal of any of their number is when to make room for one per-manent tooth two or more temporary ones would require extraction,—as of course space is thus provided at the expense of the second permanent tooth, for which one of the two temporary ones was keeping a place. In this set, however, the objection to removal of any of its series is greatly obviated by the fact that, while the teeth are very soon to be lost at all events, the jaw is increasing in size and progressively affording more and more room itself for the incoming second set. Along with extraction, in the great majority of instances pressure requires to be applied to the misplaced teeth in order to effect their regulation. This has generally to be continuously kept up for a con-siderable period, and in many cases requires to be main-tained after the teeth have been restored to their natural position in order to keep them there until they seem settled in the new locality. Various forms of what are called regulating plates are used for the purpose of applying pres-sure in this manner, and may be said generally to consist of a framework fitted and fixed to the adjoining teeth something in the same manner as an artificial set, and cal-culated to afford a fixed point or fulcrum from which to act' on the tooth to be moved.

In disease of the dental tissues it is not always necessary to remove the affected organ ; such an extreme measure as this is only called for when other remedial means have failed, or appear hopeless. The chief of all dental diseases demanding the dentist's care is, as has been already stated, that known as caries, or decay. It is this affection directly or indirectly that leads to by far the larger number of ex-tractions performed; but it by no means follows that extraction is the only remedy at our command. Many teeth are extracted which might be saved, and the principal method by which this can be effected is by what is termed stopping, or plugging, or filling the teeth.

Stopping.—The operation of stopping a decayed tooth consists in cleaning out the carious cavity and removing all the softened or disintegrated tissue, and shaping and trim-ming it so as to reduce it to a form fit for receiving and retaining the material with which it is to be filled up. Along with these proceedings it in general becomes necessary to diminish the sensitive condition in which the interior surface of the prepared cavity is left, to remove or destroy any of the vascular and highly nervous pulp which may be protruding into it, and to subdue any inflammation and arrest any discharge which may have been going on in the fang. Various applications and other remedial measures are resorted to for these purposes, the most common being the applying for a time some of the more convenient escharotics on a plug inserted into and left within the cleaned-out cavity till this end is achieved. When thus prepared, the cavity is ready to be filled with whatever substance has been selected to replace the lost tissue, and as nearly as possible to restore the contour of the tooth. The substances employed as permanent stop-pings are generally metallic. Gold in the form of foil, or in that condition known as sponge gold, tin in the form of foil, and amalgams, composed of various metals either in a simple or compound condition combined with mercury, are the principal materials in use as stoppings. The oxychlorides, from their being capable of insertion in a plastic state, and quickly acquiring a density and hardness approaching that of tooth bone, are also favourites with many as serviceable fillings ; and various preparations of gutta-percha, gum resins, sulphur, and other matters have long been known as valuable, though not very durable, when employed in certain cases.

Dexterity in the insertion of a gold or other foil filling is a matter which can be acquired by experience alone. The general principles are that, the cavity being prepared and shaped as already described, the gold plug should be secured and consolidated piece by piece, until there is built up a mass filling every part of the vacant space with a uniform consistency of metal which, when finished, ought to present the feeling of being as hard as a piece of solid gold.

The other fillings are more easily dealt with. The same careful preparatory steps are requisite in all fillings, but the insertion of the plug in amalgam and other stoppings being performed while the material is in a plastic condition, the process is rendered much more simple. The cavity should be completely filled, but not over-filled, and the amalgams ought to be used with as little mercury as is at all possible. A number of instruments are necessary for effecting all these various manipulations, but to describe them here would be as unintelligible as it appears unnecessary. Excavators, enamel cutters, burr head drills, points, pluggers, burnishers, &c, are only some of those required; while their modes of use are either by the hand or by mechanical-apparatus, such as what are termed burring-engines, &c. Stopping may be regarded as one of the most valuable operations in modern dentistry; and although itds no guarantee that the tooth stopped is ever after safe from the renewed attack of caries any more than its unstopped neighbours are from its original attack, yet it is surprising how few well-filled teeth are lost by caries recommencing in the stopped cavity.

Besides those already mentioned, the teeth and jaws are subject to a number of disorders and lesions which it would be out of place here to do more than enumerate. Fracture and dislocation of the teeth, ulceration and absorption of the gum, necrosis and exfoliation of the jaw, alteration in the secretions of the mouth, the deposit of tartar or salivary calculus on the teeth or in the salivary ducts, the effect of various medicines and poisonous agents on the teeth, jaws, and mouth generally,—these and the like matters are all of much interest, and more or less connected with dentistry proper. But for information in regard to them the reader must be referred to the various excellent publications treat-ing of them, which have appeared in considerable numbers since dental surgery has occupied more notice and taken a place as one of the recognized specialities of medicine.

Mechanical dentistry, properly so called, consists in the construction of artificial substitutes to supply the place of lost teeth. Stopping and such like operations might also be classed with mechanical dentistry as contrasted with purely surgical treatment ; as yet, however, these matters are not quite decided; and the day when the dental surgeon and the mechanical dentist—like the ophthalmic surgeon and the optician—should each occupy a separate sphere has not arrived. All that can here be given is a mere outline of the principles involved in mechanical dentistry. The subject is one comprehending a knowledge of many depart-ments of mechanical science; and to do more than indicate the nature of the various modes of construction, and the processes carried on in the manufacture of artificial teeth, would be useless and inexpedient.

The removal of roots and stumps as a preparatory step in the fitting of artificial teeth is a matter to be decided by the circumstances of the case. The length of time which can be afforded for cicatrization and absorption of the alveolar walls and gum ; the presence of adjoining teeth to be left standing, especially front teeth; the fitness of the patient for the operation of extraction,—these and other ocircumstances must determine what amount of surgical preparation is to precede the supplying of false teeth. As a general rule, the clearer the gums are of stumps and decayed teeth the better ; but at the same time certain ad-vantages, transitory as they may be, are in some instances to be derived from their retention.

The jaw, gum, and teeth being then considered as in a suitable condition, the first step in the process is to obtain a plaster cast of the parts,—" the model," as it is termed. This is done by pressing softened beeswax or some similarly plastic composition against them until they are imbedded and leave an impression in it, giving an exact mould of the gums, remaining teeth, and all other parts on its removal. Plaster of Paris is now run into the mould so obtained, and when this is set and hardened a perfect facsimile of the structures to be fitted is the result.

Any further proceedings now depend upon the mode and material in which the future artificial set is to be con-structed. Every set of artificial teeth consists of represen-tatives of the lost organs, modelled in a species of porcelain, and mounted upon a base adjusted to the gum and remain-ing natural teeth. This base is manufactured in a variety of materials, the principal of which are—(1) metal plate, of gold, platinum, silver, or different alloys; (2) vulcanized caoutchouc, or vulcanite, as it is called; and (3) celluloid base, a composition of collodion and camphor, which has not been long enough tested as yet to rank with the other substances ; while (4) the teeth may be mounted merely with as much extraneous material as will support a pin or pivot by which they may be attached as new crowns to a root in which such pivot is firmly inserted. When it is intended that the base shall be of gold or other plate, a metal die and counter have to be made from the plaster model, between which dies the plate is embossed, and the requisite form obtained. The die and counter die are generally made the one in zinc or gun metal, the other in lead or tin; and—unlike the dies from which jewellery patterns, &c, are embossed, and which may serve for thousands of times—the dental dies, having served to emboss the plate for one patient, are of no further use for any other case. The plate being thus far advanced next requires to be adjusted to the mode in which the patient closes the opposing jaw or teeth against it in shutting the mouth—in other words, the "bite" has to be taken, and the artificial teeth, which are to be mounted on the plate, arranged accordingly. Any fastenings supporting or steady-ing the set have also to be adjusted; and after this, if every-thing has gone well, the false set should be ready for placing in its destined locality and for use by the wearer.

Should it be proposed to make the base of vulcanite, celluloid base, or a similar material, a different mode of procedure must be adopted. These materials necessitate a greater bulk of substance occupying the mouth than is the case where metal plate is employed. This, however, is in some cases an advantage—since, for instance, where the gum has been greatly diminished in size through absorption, it requires some bulk of material to restore the parts to their normal size, and to give the former natural expression to the features. In preparing a vulcanite base no metal die is necessary. The base is built up in wax directly on the plaster model, and the porcelain teeth adjusted in their places, the bite and attachments being carefully attended to, as described in speaking of plate cases. The set thus made up, and presenting the exact counterpart of what the finished work is intended to be, is now, after testing it and finding it correct and perfect in the mouth, imbedded in Paris plaster as follows. A small box, or " flask," as it is denominated, of iron or other metal, like one saucer inverted on the top of another, is opened and the model with the wax-built set on it is placed in the lower saucer, which is then filled up with plaster to the level of the wax set. This being allowed to harden is soaped or oiled all over its surface, and the lid of the flask, or what corres-ponds to the upper saucer, is now placed upon the under portion of the flask. An opening in this covering portion enables plaster to be next poured into it till the inclosed wax-mounted set is shut up like a fossil in the heart of its stohy covering. On the two halves of the flask being separated, the set of course remains firmly secured in the lower portion. Boiling water is now poured over it, and the wax thus melted out, leaving the porcelain teeth undis-turbed and in situ. A cavity is thus left when the two sides of the flask are again closed, representing exactly the form of the wax removed. Baw vulcanite, or whatever other material of the kind is to be used, is now introduced with care into the space thus left by the removal of the wax. The two sides of the flask are next brought together and maintained there by the pressure of a clamp and sccew. The whole is then placed in a vessel termed a vulcanizer, where it is subjected, for the space of from an hour and a quarter to two hours or more, to the action of steam at a temperature ranging up to 320° Fahr., at the end of which time the piece will be found hard and ready for finishing and polishing as may be desirable. In firing and manipulating the celluloid base some modification of this process is required, but as yet the substance is com-paratively little used, and would scarcely justify further remark in this place.

What is termed a pivot tooth, again, is an artificial tooth having a metal or sometimes a wooden pin firmly attached to it; and this being inserted into the opened pulp cavity of a healthy fang, the artificial forms a secure and very perfect substitute for the original crown when destroyed by caries, broken off, or otherwise lost.

The use of artificial teeth, especially by those previously unaccustomed to them, requires considerable practice and no small amount of perseverance. The larger the artificial set,—that is, the greater the number of teeth replaced,— the greater the difficulties and the more the discomfort ex perienced. Time, however, works wonders here as in many other instances. It is not an uncommon thing to find a set which never has fitted well, or one which owing to many years of use does not fit well, being felt so com-fortable, through mere habit of wearing it, that on a new and perfectly fitting set being made, the old one, with all its faults, is preferred to the other. A few days' wear, however, of the new one generally brings all the short-comings of the old glaringly out on its being again attempted to be worn. And in the same manner, a week or two's perseverance generally enables any ordinary set to be worn and used with comfort and facility even by patients who are for the first time under the dentist's care. Various modes of fixation are adopted for the retaining of artificial teeth in their proper situation. Atmospheric pressure, or " suction," as it is termed, is the simplest of all, being merely the hold established between the palate and the set in the same way as occurs between a wet leather " sucker " and the stone it lifts. Another method is by what are termed " spiral springs," a mode only applicable, however, where both an upper and lower set are worn at the same time. And a third style of fixation is where the set is supported upon certain natural teeth among those remaining in the patient's jaw. Each mode has its own advantages, and sometimes one or other method is the only one at all possible to be adopted. This, however, is seldom a difficult matter to decide by any one who has had much experience of either the operating room or the dental work-shop.

The art of dentistry is difficult to acquire, and com-prehends in itself processes appertaining to several separate branches of manufacture. It is, however, an art which is an extremely useful one, and has done valuable service, since it is not too much to say that in all probability many lives have been saved and a still greater number prolonged through the instrumentality of the aid afforded by the use of artificial teeth.

Literature of the subject and authorities on Dental Surgery.— Goodsir, Edinburgh Medical Journal, 1838 ; Heath, On Diseases of the Jaws, 1868 ; Owen, On the Skeleton and Teeth, 1855 ; Tome's Dental Surgery, 1873 ; Taft's Operative Dentistry, 1877; Salter's Dental Pathology, 1874 ; Smith's Dental Anatomy and Surgery, 1864, and various papers in Edinburgh Medical Journal, Proceedings of Royal Society of Edinburgh, &c, from 1852 ; Cole's Dental Mechanics, 1876 ; Waldeyer, in Strieker's Handbuch, 1870 ;
Turner's Human Anatomy, 1877 ; Richardson's Mechanical Dentistry, 1860; Wedl's Pathology of the Teeth, 1860 ; various papers, by Kolliker, Arnold, Boll, Robin and Magitot, Huxley, 4c., in British and Continental journals. (J. S.*l




Footnotes

Indeed it is comparatively of late years that dentistry has occupied anything like a properly recognized position among the different departments of minor surgery ; for long it was practised to a large extent as a superadded means of livelihood by persons engaged in some other pursuit, and without any professional education whatever. The blacksmith, barber, watchmaker, and others of the same class were the dentists of every village and country town ;' while even in some of our larger cities dentists of the kind were till lately to be found practising under the very shadow of universities and medical schools. The explanation of this seems to have been that mere tooth-drawing constituted the surgical dentistry of these days ; and as the operation is one demanding muscular strength and manual dexterity more than anatomical knowledge or surgical skill, and was performed as successfully in many cases by the irregular as by the regular practitioners, it had not many attractions for medical men. It was accordingly consigned to the uneducated and the charlatan, who did not fail with proverbial unscrupulousness to parade their specialty as sufficient to confer a surgical status on those performing it, and entitle them to the designation of surgeon dentist,—a designation which has ever since been applied without discrimination or distinction to qualified or unqualified practitioners in this particular branch. In 1840 or 1841 this state of matters seems to have attracted the atten-tion of the profession, since, after much consideration, some anxiety was manifested by its more respectable members to be recognized in. the new Medical Act of 1843, then being introduced by Sir James Graham. Both then and later, however, the fully qualified medical men objected to the fractionally qualified being made to appear as on an equal footing with themselves. The profession may at this time be said to have divided itself into three sections—1st, those who desired to see all dentists fully qualified surgeons ; 2d, those who wished them to have only a certain amount of surgical knowledge.


For anatomy of the dental system see p 232 of the present volume.






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