The teeth are hard white or yellowish-white structures, implanted in the
alveoli of the bones of the jaws—premaxilla, maxilla, and mandible.
Morphologically they are large calcified papillæ. Functionally they are
organs of prehension and mastication, and may serve as weapons of
offense and defense. They are classified according to form and position
as follows:
1. =The incisor teeth= (Dentes incisivi) are situated in front and are
implanted in the premaxilla and mandible.
2. =The canine teeth= (Dentes canini) are situated a little further
back, at or near the premaxillary suture in the upper jaw; in the lower
jaw they are nearer the incisors.
3. =The cheek teeth= (Dentes premolares et molares), the remaining
teeth, occupy the sides of the dental arch. The space between the
incisors and cheek teeth is termed the interdental or interalveolar
space. It is customary to divide the cheek teeth into an anterior
series, termed =premolars=, which appear as temporary, deciduous, or
milk teeth, and are replaced by permanent successors, and a posterior
series, the =molars=, which appear only as permanent teeth without
deciduous predecessors.
As the teeth of the two sides of the jaws are alike in number and
character (in normal cases), the complete dentition may be briefly
indicated by a =dental formula= such as the following:
( 2 1 2 3 )
2 ( I - C - P - M - ) = 32.
( 2 1 2 3 )
In this formula the letters indicate the kinds of teeth, and the figures
above and below the lines give the number of teeth of one side in the
upper and lower jaw respectively in man.
The individual teeth of each group are designated numerically, the
starting-point being the middle line; thus the incisor on either side of
the middle line is the first incisor, and may be conveniently indicated
by the notation I^1. The temporary or deciduous teeth may be designated
in a similar manner, prefixing D (for deciduous) to the letter
indicating the kind of tooth. In addition to the above systematic method
of notation other terms have received the sanction of popular usage.
Thus the first incisors are commonly called “pinchers,” or “nippers”;
the second, intermediate; and the third, corner teeth. The canines, when
highly developed, may be termed tusks or fangs. The vestigial and
inconstant first premolar of the horse is popularly termed the “wolf
tooth.”
Each tooth presents for description a portion coated with enamel, termed
the =crown= (Corona dentis), and a portion covered with cement, termed
the =root= (Radix dentis). The line of union of these parts is the neck
(Collum dentis).[80] In many teeth the neck is distinct and is embraced
by the gum, _e. g._, the teeth of the dog and the temporary incisors of
the horse. In other teeth no constriction is seen, as in the permanent
incisors of the horse. Between these extremes may be noted the molars of
the horse, in which the neck is seen only in advanced age.
The =surface= of a tooth directed toward the lips is termed =labial=;
toward the cheek, =buccal=; and toward the tongue, =lingual= (Facies
labialis, buccalis, lingualis). The surface opposed to a neighboring
tooth of the same dental arch is termed the =contact surface= (Facies
contactus). The grinding or =masticatory= or “table” surface (Facies
masticatoria) is that which comes in contact with a tooth or teeth of
the opposite jaw.
=Structure.=—Teeth are composed of four tissues, which are considered
here from within outward. The =pulp= (Pulpa dentis) is a soft gelatinous
tissue, which occupies a space in the central part of the tooth termed
the =pulp cavity= (Cavum dentis). The pulp is well supplied with
blood-vessels and nerves. It occupies a relatively large space in young
growing teeth, but later the dentine deposited on its surface gradually
encroaches on it until, in advanced age, the cavity is obliterated or
much reduced. The =dentine= (Substantia eburnea) forms the bulk of most
teeth, covering the surface of the pulp. It is very hard, and is
yellowish-white in color. The =enamel= (Substantia adamantina)
constitutes a layer of varying thickness covering the dentine of the
crown of the tooth. It is easily distinguished by its clear bluish-white
appearance and its extreme density. The =cement= (Substantia ossea) is
always the outermost tooth substance. In simple teeth it forms usually a
thin layer on the surface of the dentine of the root only, but in
complex teeth it exists in considerable quantity, tending to fill in the
spaces between the enamel folds of the crown also. Its structure is
practically the same as that of bone without Haversian canals, and even
these occur where the cement forms a very thick layer. The embedded part
of the tooth is attached to the alveolus by a vascular layer of
connective tissue, the =alveolar periosteum= (Periosteum alveolare),
which constitutes the periosteum at once of tooth and alveolus.
The =blood-supply= to the pulp is derived from the alveolar or dental
branches of the internal artery; the =nerve-supply= comes from branches
of the trigeminus.