Teeth

Teeth (dentes) are important anatomical formations located in the dental alveoli of the jaws. Depending on the features of the structure, position and function, several groups of teeth are distinguished: incisors, canines, small molars, or premolars, and large molar molars.

The incisors are intended mainly for grasping food and biting, canines for crushing, root teeth for grinding, grinding food. Despite the subdivision of the teeth into different groups, all the teeth have a common plan of the structure. The tooth is divided into a crown, a neck and a root.

The crown of the tooth (corona dentis), the most massive part protruding above the gum, has several surfaces. The tongue surface (facies lingualis) of the crown faces the tongue, the facies (facies vestibularis, seu facialis) - towards the mouth, the contact surface (facies contactus) - to the adjacent tooth. Females masticatoria, or facies occlusiatus, similar teeth of the upper and lower jaws face each other.

Inside the crown is the cavity of the crown (cavitas coronalis), containing pulp and continuing into the canal of the root of the tooth.

The root of the tooth (radix dentes) is in the dental alveolus, with the walls of which it is connected by a special kind of synarthrosis - vkolachivaniem. Each tooth has from one (incisors, canines) to two or three (molars) roots. Inside each root there is a canal of the tooth (canalis radicis dentis), also filled with pulp. The root of the tooth ends with apex (apex radicis dentis), which has an opening through which the artery, nerve, and vein enter the cavity of the tooth.

Between the crown and the root is the neck of the tooth (cervix dentis), which covers the mucous membrane of the gum.

The pulpa of the tooth (pulpa dentis) is formed by a loose fibrous connective tissue, in which the blood vessels and nerve branch.

The main mass of the tooth forms dentin (dentinum). In the area of the crown, dentin is covered with enamel, in the region of the neck of the tooth and its root - with cement.

Enamel (enamelum) is a very strong substance. It is built of enamel prisms 3-5 microns thick, separated from each other by an interprismatic component. This component has a lower electron density than enamel. The free surface of the enamel is covered with a thin cuticle. In general, the enamel consists of inorganic salts (96-97%), among which calcium phosphate and calcium carbonate predominate. In enamel contains almost 4% of calcium fluoride. In dentine there are about 28% of organic substances (mainly collagen) and 72% of inorganic substances. Among inorganic compounds, calcium phosphate, magnesium phosphate and calcium fluoride are predominant.

Cement in its structure resembles bone tissue. It is formed by conventionalized plates, between which there are multistep cementocytes, located in lacunae. In the cement penetrate the collagen (Sharpeyev) fibers, which tightly bind the root of the tooth with periodontium. In the region of the neck of the tooth, cement is depleted, deprived of cells (cell-free cement). The composition of cement includes 29.6% of organic substances and 70.4% of inorganic compounds (mainly calcium phosphate and calcium carbonate).

Distinguished milk and permanent teeth.

Milk teeth (dentes decidui) in the amount of 20 appear in the child after birth, starting from 5-7 months of life. At the age of 5-7 years, the baby's teeth fall out and are replaced by permanent teeth (dentes permanentes), the number of which in an adult reaches 32. Milk teeth, as compared to permanent teeth, have relatively wider and short crowns and short roots. The child has 2 incisors, 1 canine, 2 large molars on each maxillary bone and half of the lower jaw. Small molar teeth are absent (0).

Timing of eruption of dairy and permanent teeth

Tooth	Jaw	Terms of teething
		Milk, months	Permanent, years
Medial cutter	Upper Lower	7-8 5-7	7-8 6-7
Lateral cutter	Upper Lower	8-9 7-8	8-9 7-8
Fang	Upper Lower	18-20 16-18	11-12 9-10
First small molar tooth (premolar)	Upper Lower	- -	10-11 10-12
Second small molar tooth (premolar)	Upper Lower	- -	10-12 11-12
The first large molar (molar)	Upper Lower	14-15 12-13	6-7 6-7
The second large molar (molar)	Upper Lower	21-24 20-22	12-13 11-13
The third large molar tooth (molar)	Upper Lower	- -	17-21 12-26

In numerical terms, the formula of infant teeth is as follows:

2012	2102
2012	2102

In this formula, the upper row indicates the upper teeth, the lower row indicates the lower teeth. The vertical line separates the teeth of the right side from the teeth of the left side. Each digit indicates the number of teeth of a certain shape.

Before the eruption of the permanent tooth, the corresponding milk tooth falls out. Erection of permanent teeth begins at 6-7 years and lasts up to 13-15 years. The first are the lower large molars, then the medial incisors and the first upper molars, the lateral incisors after them. Later the first molars appear, after them the fangs, then the second small molars, and after them the second large molars. The last (aged 22-26 years) erupts third large molars, or wisdom teeth. On each half of the upper jaw and each half of the lower jaw there are 8 permanent teeth: 2 incisors, 1 canine, 2 small molars and 3 large molars.

The tooth formula of permanent teeth is as follows:

3212	2123
3212	2123

Incisors (dentes incisivi) have a flattened wide crown with a cutting surface. Crown of upper incisors wider than lower ones. The root of the incisors is single, conical; the root of the lower incisor is compressed laterally. Depending on the location with respect to the median plane, the lateral and medial incisors are distinguished.

Fangs (dentes canini) have a crown conical, pointed. The root is single, long, squeezed from the sides. The root of the lower canines is shorter than the upper ones. Sometimes the root of the lower canines is bifurcated.

Small molars (premolars - dentes premolares) are behind the canine. The crown of premolars on the side of the chewing surface is round or oval, and has two chewing tubercles. The height of the crown is smaller than that of the fangs. The root of premolars is single, conical in shape, sometimes it is bifurcated at the upper premolar.

Large molars (molars - dentes molares) are located behind the premolars. The crown of large molars is usually cubic in shape, on the masticatory surface there are 3-5 tubercles. Large molars of the upper jaw have 3, the lower - 2 roots. Dimensions of molars decrease from front to back. The third molar (wisdom tooth - dens serotinus) is the smallest in size.