Historical sketch.
(from Lat. _dens_, a tooth), a special department of medical
science, embracing the structure, function and therapeutics of the mouth
and its contained organs, specifically the teeth, together with their
surgical and prosthetic treatment. (For the anatomy of the teeth see
TEETH.) As a distinct vocation it is first alluded to by Herodotus (500
B.C.). There are evidences that at an earlier date the Egyptians and
Hindus attempted to replace lost teeth by attaching wood or ivory
substitutes to adjacent sound teeth by means of threads or wires, but
the gold fillings reputed to have been found in the teeth of Egyptian
mummies have upon investigation been shown to be superficial
applications of gold leaf for ornamental purposes. The impetus given to
medical study in the Grecian schools by the followers of Aesculapius and
especially Hippocrates (500 to 400 B.C.) developed among the
practitioners of medicine and surgery considerable knowledge of
dentistry. Galen (A.D. 131) taught that the teeth were true bones
existing before birth, and to him is credited the belief that the upper
canine teeth receive branches from the nerve which supplies the eye, and
hence should be called "eye-teeth." Abulcasis (10th cent. A.D.)
describes the operation by which artificial crowns are attached to
adjacent sound teeth. Vesalius (1514), Ambroise Paré, J. J. Scaliger, T.
Kerckring, M. Malpighi, and lesser anatomists of the same period
contributed dissertations which threw some small amount of light upon
the structure and functions of the teeth. The operation of transplanting
teeth is usually attributed to John Hunter (1728-1793), who practised it
extensively, and gave to it additional prominence by transplanting a
human tooth to the comb of a cock, but the operation was alluded to by
Ambroise Paré (1509-1590), and there is evidence to show that it was
practised even earlier. A. von Leeuwenhoek in 1678 described with much
accuracy the tubular structure of the dentine, thus making the most
important contribution to the subject which had appeared up to that
time. Until the latter part of the 18th century extraction was
practically the only operation for the cure of toothache.
The early contributions of France exerted a controlling influence upon
the development of dental practice. Urbain Hémard, surgeon to the
cardinal Georges of Armagnac, whom Dr Blake (1801) calls an ingenious
surgeon and a great man, published in 1582 his _Researches upon the
Anatomy of the Teeth, their Nature and Properties_. Of Hémard, M.
Fauchard says: "This surgeon had read Greek and Latin authors, whose
writings he has judiciously incorporated in his own works." In 1728
Fauchard, who has been called the father of modern dentistry, published
his celebrated work, entitled _Le Chirurgien Dentiste ou traité des
dents_. The preface contains the following statement as to the existing
status of dental art and science in France, which might have been
applied with equal truth to any other European country:--" The most
celebrated surgeons having abandoned this branch of surgery, or having
but little cultivated it, their negligence gave rise to a class of
persons who, without theoretic knowledge or experience, and without
being qualified, practised it at hazard, having neither principles nor
system. It was only since the year 1700 that the intelligent in Paris
opened their eyes to these abuses, when it was provided that those who
intended practising dental surgery should submit to an examination by
men learned in all the branches of medical science, who should decide
upon their merits." After the publication of Fauchard's work the
practice of dentistry became more specialized and distinctly separated
from medical practice, the best exponents of the art being trained as
apprentices by practitioners of ability, who had acquired their training
in the same way from their predecessors. Fauchard suggested porcelain as
an improvement upon bone and ivory for the manufacture of artificial
teeth, a suggestion which he obtained from R. A. F. de Réaumur, the
French savant and physicist, who was a contributor to the royal
porcelain manufactory at Sévres. Later, Duchateau, an apothecary of St
Germain, made porcelain teeth, and communicated his discovery to the
Academy of Surgery in 1776, but kept the process secret. Du Bois Chémant
carried the art to England, and the process was finally made public by
M. Du Bois Foucou. M. Fonzi improved the art to such an extent that the
Athenaeum of Arts in Paris awarded him a medal and crown (March 14,
1808).
In Great Britain the 19th century brought the dawning of dental science.
The work of Dr Blake in 1801 on the anatomy of the teeth was distinctly
in advance of anything previously written on the subject. Joseph Fox was
one of the first members of the medical profession to devote himself
exclusively to dentistry, and his work is a repository of the best
practice of his time. The processes described, though comparatively
crude, involve principles in use at the present time. Thomas Bell, the
successor of Fox as lecturer on the structure and disease of the teeth
at Guy's Hospital, published his well-known work in 1829. About this
period numerous publications on dentistry made their appearance, notably
those of Koecker, Johnson and Waite, followed somewhat later by the
admirable work of Alexander Nasmyth (1839). By this time Cuvier, Serres,
Rousseau, Bertin, Herissant and others in France had added to the
knowledge of human and comparative dental anatomy, while M. G. Retzius,
of Sweden, and E. H. Weber, J. C. Rosenmüller, Schreger, J. E. von
Purkinje, B. Fraenkel and J. Müller in Germany were carrying forward the
same lines of research. The sympathetic nervous relationships of the
teeth with other parts of the body, and the interaction of diseases of
the teeth with general pathological conditions, were clearly
established. Thus a scientific foundation was laid, and dentistry came
to be practised as a specialty of medicine. Certain minor operations,
however, such as the extraction of teeth and the stopping of caries in
an imperfect way, were still practised by barbers, and the empirical
practice of dentistry, especially of those operations which were almost
wholly mechanical, had developed a considerable body of dental artisans
who, though without medical education in many cases, possessed a high
degree of manipulative skill. Thus there came to be two classes of
practitioners, the first regarding dentistry as a specialty of medicine,
the latter as a distinct and separate calling.
In America representatives of both classes of dentists began to arrive
from England and France about the time of the Revolution. Among these
were John Wooffendale (1766), a student of Robert Berdmore of Liverpool,
surgeon-dentist to George III.; James Gardette (1778), a French
physician and surgeon; and Joseph Lemaire (1781), a French dentist who
went out with the army of Count Rochambeau. During the winter of
1781-1782, while the Continental army was in winter quarters at
Providence, Rhode Island, Lemaire found time and opportunity to practise
his calling, and also to instruct one or two persons, notably Josiah
Flagg, probably the first American dentist. Dental practice was thus
established upon American soil, where it has produced such fertile
results.
Course of training.
Until well into the 19th century apprenticeship afforded the only means
of acquiring a knowledge of dentistry. The profits derived from the
apprenticeship system fostered secrecy and quackery among many of the
early practitioners; but the more liberal minded and better educated of
the craft developed an increasing opposition to these narrow methods. In
1837 a local association of dentists was formed in New York, and in 1840
a national association, The American Society of Dental Surgeons, the
object of which was "to advance the science by free communication and
interchange of sentiments." The first dental periodical in the world,
_The American Journal of Dental Science_, was issued in June 1839, and
in November 1840 was established the Baltimore College of Dental
Surgery, the first college in the world for the systematic education of
dentists. Thus the year 1839-1840 marks the birth of the three factors
essential to professional growth in dentistry. All this, combined with
the refusal of the medical schools to furnish the desired facilities for
dental instruction, placed dentistry for the time being upon a footing
entirely separate from general medicine. Since then the curriculum of
study preparatory to dental practice has been systematically increased
both as to its content and length, until in all fundamental principles
it is practically equal to that required for the training of medical
specialists, and in addition includes the technical subjects peculiar to
dentistry. In England, and to some extent upon the continent, the old
apprenticeship system is retained as an adjunct to the college course,
but it is rapidly dying out, as it has already done in America. Owing to
the regulation by law of the educational requirements, the increase of
institutions devoted to the professional training of dentists has been
rapid in all civilized countries, and during the past twenty years
especially so in the United States. Great Britain possesses upwards of
twelve institutions for dental instruction, France two, Germany and
Switzerland six, all being based upon the conception that dentistry is a
department of general medicine. In the United States there were in 1878
twelve dental schools, with about 700 students; in 1907 there were
fifty-seven schools, with 6919 students. Of these fifty-seven schools,
thirty-seven are departments of universities or of medical institutions,
and there is a growing tendency to regard dentistry from its educational
aspect as a special department of the general medical and surgical
practice.
Research.
Recent studies have shown that besides being an important part of the
digestive system, the mouth sustains intimate relationship with the
general nervous system, and is important as the portal of entrance for
the majority of the bacteria that cause specific diseases. This fact has
rendered more intimate the relations between dentistry and the general
practice of medicine, and has given a powerful impetus to scientific
studies in dentistry. Through the researches of Sir J. Tomes, Mummery,
Hopewell Smith, Williams and others in England, O. Hertwig, Weil and
Röse in Germany, Andrews, Sudduth and Black in America, the minute
anatomy and embryology of the dental tissues have been worked out with
great fulness and precision. In particular, it has been demonstrated
that certain general systemic diseases have a distinct oral expression.
Through their extensive nervous connexions with the largest of the
cranial nerves and with the sympathetic nervous system, the teeth
frequently cause irritation resulting in profound reflex nervous
phenomena, which are curable only by removal of the local tooth
disorder. Gout, lithaemia, scurvy, rickets, lead and mercurial
poisoning, and certain forms of chronic nephritis, produce dental and
oral lesions which are either pathognomonic or strongly indicative of
their several constitutional causes, and are thus of great importance in
diagnosis. The most important dental research of modern times is that
which was carried out by Professor W. D. Miller of Berlin (1884) upon
the cause of caries of the teeth, a disease said to affect the human
race more extensively than any other. Miller demonstrated that, as
previous observers had suspected, caries is of bacterial origin, and
that acids play an important rôle in the process. The disease is brought
about by a group of bacteria which develop in the mouth, growing
naturally upon the débris of starchy or carbohydrate food, producing
fermentation of the mass, with lactic acid as the end product. The
lactic acid dissolves the mineral constituent of the tooth structure,
calcium phosphate, leaving the organic matrix of the tooth exposed.
Another class of germs, the peptonising and putrefactive bacteria, then
convert the organic matter into liquid or gaseous end products. The
accuracy of the conclusions obtained from his analytic research was
synthetically proved, after the manner of Koch, by producing the disease
artificially. Caries of the teeth has been shown to bear highly
important relation to more remote or systemic diseases. Exposure and
death of the dental pulp furnishes an avenue of entrance for
disease-producing bacteria, by which invasion of the deeper tissues may
readily take place, causing necrosis, tuberculosis, actinomycosis,
phlegmon and other destructive inflammations, certain of which,
affecting the various sinuses of the head, have been found to cause
meningitis, chronic empyema, metastatic abscesses in remote parts of the
body, paralysis, epilepsy and insanity.
Filling or stopping.
_Operative Dentistry._--The art of dentistry is usually divided
arbitrarily into _operative dentistry_, the purpose of which is to
preserve as far as possible the teeth and associated tissues, and
_prosthetic dentistry_, the purpose of which is to supply the loss of
teeth by artificial substitutes. The filling of carious cavities was
probably first performed with lead, suggested apparently by an operation
recorded by Celsus (100 B.C.), who recommended that frail or decayed
teeth be stuffed with lead previous to extraction, in order that they
might not break under the forceps. The use of lead as a filling was
sufficiently prevalent in France during the 17th century to bring into
use the word _plombage_, which is still occasionally applied in that
country to the operation of filling. Gold as a filling material came
into general use about the beginning of the 19th century.[1] The earlier
preparations of gold were so impure as to be virtually without cohesion,
so that they were of use only in cavities which had sound walls for its
retention. In the form of rolls or tape it was forced into the
previously cleaned and prepared cavity, condensed with instruments under
heavy hand pressure, smoothed with files, and finally burnished. Tin
foil was also used to a limited extent and by the same method.
Improvements in the refining of gold for dental use brought the product
to a fair degree of purity, and, about 1855, led to the invention by Dr
Robert Arthur of Baltimore of a method by which it could be welded
firmly within the cavity. The cohesive properties of the foil were
developed by passing it through an alcohol flame, which dispelled its
surface contaminations. The gold was then welded piece by piece into a
homogeneous mass by plugging instruments with serrated points. In this
process of cold-welding, the mallet, hitherto in only limited use, was
found more efficient than hand pressure, and was rapidly developed. The
primitive mallet of wood, ivory, lead or steel, was supplanted by a
mallet in which a hammer was released automatically by a spring
condensed by pressure of the operator's hand. Then followed mallets
operated by pneumatic pressure, by the dental engine, and finally by the
electro-magnet, as utilized in 1867 by Bonwill. These devices greatly
facilitated the operation, and made possible a partial or entire
restoration of the tooth-crown in conformity with anatomical lines.
The dental engine in its several forms is the outgrowth of the simple
drill worked by the hand of the operator. It is used in removing decayed
structure and for shaping the cavity for inserting the filling. From
time to time its usefulness has been extended, so that it is now used
for finishing fillings and polishing them, for polishing the teeth,
removing deposits from them and changing their shapes. Its latest
development, the _dento-surgical engine_, is of heavier construction and
is adapted to operations upon all of the bones, a recent addition to its
equipment being the spiral osteotome of Cryer, by which, with a minimum
shock to the patient, fenestrae of any size or shape in the brain-case
may be made, from a simple trepanning operation to the more extensive
openings required in intra-cranial operations. The rotary power may be
supplied by the foot of the operator, or by hydraulic or electric
motors. The rubber dam invented by S. C. Barnum of New York (1864)
provided a means for protecting the field of operations from the oral
fluids, and extended the scope of operations even to the entire
restoration of tooth-crowns with cohesive gold foil. Its value has been
found to be even greater than was at first anticipated. In all
operations involving the exposed dental pulp or the pulp-chamber and
root-canals, it is the only efficient method of mechanically protecting
the field of operation from invasion by disease-producing bacteria.
The difficulty and annoyance attending the insertion of gold, its high
thermal conductivity, and its objectionable colour have led to an
increasing use of amalgam, guttapercha, and cements of zinc oxide mixed
with zinc chloride or phosphoric acid. Recently much attention has been
devoted to restorations with porcelain. A piece of platinum foil of .001
inch thickness is burnished and pressed into the cavity, so that a
matrix is produced exactly fitting the cavity. Into this matrix is
placed a mixture of powdered porcelain and water or alcohol, of the
colour to match the tooth. The mass is carefully dried and then fused
until homogeneous. Shrinkage is counteracted by additions of porcelain
powder, which are repeatedly fused until the whole exactly fills the
matrix. After cooling, the matrix is stripped away and the porcelain is
cemented into the cavity. When the cement has hardened, the surface of
the porcelain is ground and polished to proper contour. If successfully
made, porcelain fillings are scarcely noticeable. Their durability
remains to be tested.
Dental therapeutics.
Until recent times the exposure of the dental pulp inevitably led to its
death and disintegration, and, by invasion of bacteria via the pulp
canal, set up an inflammatory process which eventually caused the loss
of the entire tooth. A rational system of therapeutics, in conjunction
with proper antiseptic measures, has made possible both the conservative
treatment of the dental pulp when exposed, and the successful treatment
of pulp-canals when the pulp has been devitalized either by design or
disease. The conservation of the exposed pulp is affected by the
operation of capping. In capping a pulp, irritation is allayed by
antiseptic and sedative treatment, and a metallic cap, lined with a
non-irritant sedative paste, is applied under aseptic conditions
immediately over the point of pulp exposure. A filling of cement is
superimposed, and this, after it has hardened, is covered with a
metallic or other suitable filling. The utility of arsenious acid for
devitalizing the dental pulp was discovered by J. R. Spooner of
Montreal, and first published in 1836 by his brother Shearjashub in his
_Guide to Sound Teeth_. The painful action of arsenic upon the pulp was
avoided by the addition of various sedative drugs,--morphia, atropia,
iodoform, &c.,--and its use soon became universal. Of late years it is
being gradually supplanted by immediate surgical extirpation under the
benumbing effect of cocaine salts. By the use of cocaine also the pain
incident to excavating and shaping of cavities in tooth structure may
be controlled, especially when the cocaine is driven into the dentine by
means of an electric current. To fill the pulp-chamber and canals of
teeth after loss of the pulp, all organic remains of pulp tissue should
be removed by sterilization, and then, in order to prevent the entrance
of bacteria, and consequent infection, the canals should be perfectly
filled. Upon the exclusion of infection depends the future integrity and
comfort of the tooth. Numberless methods have been invented for the
operation. Pulpless teeth are thus preserved through long periods of
usefulness, and even those remains of teeth in which the crowns have
been lost are rendered comfortable and useful as supports for artificial
crowns, and as abutments for assemblages of crowns, known as
bridge-work.
The discoloration of the pulpless tooth through putrefactive changes in
its organic matter were first overcome by bleaching it with chlorine.
Small quantities of calcium hypochlorite are packed into the
pulp-chamber and moistened with dilute acetic acid; the decomposition of
the calcium salt liberates chlorine _in situ_, which restores the tooth
to normal colour in a short time. The cavity is afterwards washed out,
carefully dried, lined with a light-coloured cement and filled. More
efficient bleaching agents of recent introduction are hydrogen dioxide
in a 25% solution or a saturated solution of sodium peroxide; they are
less irritating and much more convenient in application. Unlike
chlorine, these do not form soluble metallic salts which may
subsequently discolour the tooth. Hydrogen dioxide may be carried into
the tooth structure by the electric current. In which case a current of
not less than forty volts controlled by a suitable graduated resistance
is applied with the patient in circuit, the anode being a
platinum-pointed electrode in contact with the dioxide solution in the
tooth cavity, and the cathode a sponge or plate electrode in contact
with the hand or arm of the patient. The current is gradually turned on
until two or three milliamperes are indicated by a suitable ammeter. The
operation requires usually twenty to thirty minutes.
Malposed teeth are not only unsightly but prone to disease, and may be
the cause of disease in other teeth, or of the associated tissues. The
impairment of function which their abnormal position causes has been
found to be the primary cause of disturbances of the general bodily
health; for example, enlarged tonsils, chronic pharyngitis and nasal
catarrh, indigestion and malnutrition. By the use of springs, screws,
vulcanized caoutchouc bands, elastic ligatures, &c., as the case may
require, practically all forms of dental irregularity may be corrected,
even such protrusions and retrusions of the front teeth as cause great
disfigurement of the facial contour.
Extraction.
The extraction of teeth, an operation which until quite recent times was
one of the crudest procedures in minor surgery, has been reduced to
exactitude by improved instruments, designed with reference to the
anatomical relations of the teeth and their alveoli, and therefore
adapted to the several classes of teeth. The operation has been rendered
painless by the use of anaesthetics. The anaesthetic generally employed
is nitrous oxide, or laughing-gas, the use of which was discovered in
1844 by Horace Wells, a dentist of Hartford, Conn., U.S.A. Chloroform
and ether, as well as other general anaesthetics, have been employed in
extensive operations because of their more prolonged effect; but
chloroform, especially, is dangerous, owing to its effect upon the
heart, which in many instances has suddenly failed during the operation.
Ether, while less manageable than nitrous oxide, has been found to be
practically devoid of danger. The local injection of solutions of
cocaine and allied anaesthetics into the gum-tissue is extensively
practised; but is attended with danger, from the toxic effects of an
overdose upon the heart, and the local poisonous effect upon the
tissues, which lead in numerous cases to necrosis and extensive
sloughing.
Artificial teeth.
_Dental Prosthesis._--The fastening of natural teeth or carved
substitutes to adjoining sound teeth by means of thread or wire preceded
their attachment to base-plates of carved wood, bone or ivory, which
latter method was practised until the introduction of swaged metallic
plates. Where the crown only of a tooth or those of several teeth were
lost, the restoration was effected by engrafting upon the prepared root
a suitable crown by means of a wooden or metallic pivot. When possible,
the new crown was that of a corresponding sound tooth taken from the
mouth of another individual; otherwise an artificial crown carved from
bone or ivory, or sometimes from the tooth of an ox, was used. To
replace entire dentures a base-plate of carved hippopotamus ivory was
constructed, upon which were mounted the crowns of natural teeth, or
later those of porcelain. The manufacture of a denture of this character
was tedious and uncertain, and required much skill. The denture was kept
in place by spiral springs attached to the buccal sides of the appliance
above and below, which caused pressure upon both jaws, necessitating a
constant effort upon the part of the unfortunate wearer to keep it in
place. Metallic swaged plates were introduced in the latter part of the
18th century. An impression of the gums was taken in wax, from which a
cast was made in plaster of Paris. With this as a model, a metallic die
of brass or zinc was prepared, upon which the plate of gold or silver
was formed, and then swaged into contact with the die by means of a
female die or counter-die of lead. The process is essentially the same
to-day, with the addition of numerous improvements in detail, which have
brought it to a high degree of perfection. The discovery, by Gardette of
Philadelphia in 1800, of the utility of atmospheric pressure in keeping
artificial dentures in place led to the abandonment of spiral springs. A
later device for enhancing the stability is the vacuum chamber, a
central depression in the upper surface of the plate, which, when
exhausted of air by the wearer, materially increases the adhesion. The
metallic base-plate is used also for supporting one or more artificial
teeth, being kept in place by metallic clasps fitting to, and partially
surrounding, adjacent sound natural teeth, the plate merely covering the
edentulous portion of the alveolar ridge. It may also be kept in place
by atmospheric adhesion, in which case the palatal vault is included,
and the vacuum chamber is utilized in the palatal portion to increase
the adhesion.
In the construction usually practised, porcelain teeth are attached to a
gold base-plate by means of stay-pieces of gold, perforated to receive
the platinum pins baked in the body of the tooth. The stay-pieces or
backings are then soldered to the pins and to the plate by means of
high-fusing gold solder. The teeth used may be single or in sections,
and may be with or without an extension designed in form and colour to
imitate the gum of the alveolar border. Even when skillfully executed,
the process is imperfect in that the jointing of the teeth to each
other, and their adaptation to the base-plate, leaves crevices and
recesses, in which food débris and oral secretions accumulate. To
obviate these defects the enamelled platinum denture was devised.
Porcelain teeth are first attached to a swaged base-plate of pure
platinum by a stay-piece of the same metal soldered with pure gold,
after which the interstices between the teeth are filled, and the entire
surface of the plate, excepting that in contact with the palate and
alveolar border, is covered with a porcelain paste called the body,
which is modelled to the normal contour of the gums, and baked in a
muffle furnace until vitrified. It is then enamelled with a vitreous
enamel coloured in imitation of the colour of the natural gum, which is
applied and fired as before, the result being the most artistic and
hygienic denture known. This is commonly known as the continuous gum
method. Originating in France in the early part of the 19th century, and
variously improved by several experimenters, it was brought to its
present perfection by Dr John Allen of New York about 1846-1847.
Dentures supported upon cast bases of metallic alloys and of aluminium
have been employed as substitutes for the more expensive dentures of
gold and platinum, but have had only a limited use, and are less
satisfactory.
Metallic bases were used exclusively as supports for artificial dentures
until in 1855-1856 Charles Goodyear, jun., patented in England a process
for constructing a denture upon vulcanized caoutchouc as a base. Several
modifications followed, each the subject of patented improvements.
Though the cheapness and simplicity of the vulcanite base has led to its
abuse in incompetent hands, it has on the whole been productive of much
benefit. It has been used with great success as a means of attaching
porcelain teeth to metallic bases of gold, silver and aluminium. It is
extensively used also in correcting irregular positions of the teeth,
and for making interdental splints in the treatment of fractures of the
jaws. For the mechanical correction of palatal defects causing
imperfection of deglutition and speech, which comes distinctly within
the province of the prosthetic dentist, the vulcanite base produces the
best-known apparatus. Two classes of palatal mechanism are
recognized--the obturator, a palatal plate, the function of which is to
close perforations or clefts in the hard palate, and the artificial
velum, a movable attachment to the obturator or palatal plate, which
closes the opening in the divided natural velum and, moving with it,
enables the wearer to close off the nasopharynx from the oral cavity in
the production of the guttural sounds. Vulcanite is also used for
extensive restorations of the jaws after surgical operations or loss by
disease, and in the majority of instances wholly corrects the deformity.
Modern methods.
For a time vulcanite almost supplanted gold and silver as a base for
artificial denture, and developed a generation of practitioners
deficient in that high degree of skill necessary to the construction of
dentures upon metallic bases. The recent development of crown-and-bridge
work has brought about a renaissance, so that a thorough training is
more than ever necessary to successful practice in mechanical dentistry.
The simplest crown is of porcelain, and is engrafted upon a sound
natural tooth-root by means of a metallic pin of gold or platinum,
extending into the previously enlarged root-canal and cemented in place.
In another type of crown the point between the root-end and the abutting
crown-surface is encircled with a metallic collar or band, which gives
additional security to the attachment and protects the joints from
fluids or bacteria. Crowns of this character are constructed with a
porcelain facing attached by a stay-piece or backing of gold to a plate
and collar, which has been previously fitted to the root-end like a
ferrule, and soldered to a pin which projects through the ferrule into
the root-canal. The contour of the lingual surface of the crown is made
of gold, which is shaped to conform to the anatomical lines of the
tooth. The shell-crown consists of a reproduction of the crown entirely
of gold plate, filled with cement, and driven over the root-end, which
it closely encircles. The two latter kinds of crowns may be used as
abutments for the support of intervening crowns in constructing
bridge-work. When artificial crowns are supported not by natural
tooth-roots but by soldering them to abutments, they are termed dummies.
The number of dummies which may be supported upon a given number of
roots depends upon the position and character of the abutments, the
character of the alveolar tissues, the age, sex and health of the
patient, the character of the occlusion or bite, and the force exerted
in mastication. In some cases a root will not properly support more than
one additional crown; in others an entire bridge denture has been
successfully supported upon four well-placed roots. Two general classes
of bridge-work are recognized, namely, the fixed and the removable.
Removable bridge-work, though more difficult to construct, is
preferable, as it can be more thoroughly and easily cleansed. When
properly made and applied to judiciously selected cases, the bridge
denture is the most artistic and functionally perfect restoration of
prosthetic dentistry.
The entire development of modern dentistry dates from the 19th century,
and mainly from its latter half. Beginning with a few practitioners and
no organized professional basis, educational system or literature, its
practitioners are to be found in all civilized communities, those in
Great Britain numbering about 5000; in the United States, 27,000;
France, 1600, of whom 376 are graduates; German Empire, qualified
practitioners (_Zahnärzte_), 1400; practitioners without official
qualification, 4100. Its educational institutions are numerous and well
equipped. It possesses a large periodical and standard literature in all
languages. Its practice is regulated by legislative enactment in all
countries the same as is medical practice. The business of manufacturing
and selling dentists' supplies represents an enormous industry, in
which millions of capital are invested.
AUTHORITIES.--W. F. Litch, _American System of Dentistry_; Julius
Scheff, jun., _Handbuch der Zahnheilkunde_; Charles J. Essig,
_American Text-Book of Prosthetic Dentistry_; Tomes, _Dental Anatomy_
and _Dental Surgery_; W. D. Miller, _Microörganisms of the Human
Mouth_; Hopewell Smith, _Dental Microscopy_; H. H. Burchard, _Dental
Pathology, Therapeutics and Pharmacology_; F. J. S. Gorgas, _Dental
Medicine_; E. H. Angle, _Treatment of Malocclusion of the Teeth and
Fractures of the Maxillae_; G. Evans, _A Practical Treatise on
Artificial Crown-and-Bridge Work and Porcelain Dental Art_; C. N.
Johnson, _Principles and Practice of Filling Teeth, American
Text-Book of Operative Dentistry_ (3rd ed., 1905); Edward C. Kirk,
_Principles and Practice of Operative Dentistry_ (2nd ed., 1905); J.
S. Marshall, _American Text-Book of Prosthetic Dentistry_ (edited by
C. R. Turner; 3rd ed., 1907). (E. C. K.)