The teeth are an integral part of the chewing and speech apparatus. Teeth take part in chewing, breathing, voice, and speech formation.
The root of the tooth is located in a special recess in the jaw - the alveolus. The main function of the root is to attach the tooth to the jaw using a powerful ligamentous apparatus. It is customary to divide the root horizontally into the buccal, middle, and apical parts. Vertically divided into distal, medial, middle thirds. In the medial norm, they are divided into vestibular, middle, and lingual (oral) parts.
The neck of the tooth is located between the root and the crown and is closely connected with the gingival mucosa. At the neck of the tooth, there is an important transitional element - the gingival groove. Trauma to this part of the tooth leads to the gingival recession with the opening of the transitional dentin of the enamel border, which in turn leads to further destruction of the unprotected area of the tooth.
The crown of the tooth normally protrudes above the edge of the gum. The crown is covered with enamel - the hardest, chewing part of the tooth. In the crown of the tooth is the cavity of the tooth, which passes into the tooth canal. Loose tissue is located in the tooth cavity - dental pulp, which fills the coronal and root parts of the dental cavity. Vessels and nerves pass through the pulp.
The ligamentous apparatus of the tooth consists of strong connective tissue fibers connecting the neck and root of the tooth with the bone plate located in the alveolus of the jaw. In the area of the neck, these bundles of fibers have a horizontal direction and, together with the gum and periosteum, form a circular tooth ligament, which separates the root part from the environment. The ligamentous apparatus fixes and cushions the tooth during chewing; when chewing, the load on the molar can reach 100 kg, and without such shock absorbers, trauma to the bottom of the alveoli can occur. All the ligaments, vessels, and nerves of the tooth are collectively called the periodontium.
Histologically, a tooth consists of several types of tissue. The bulk of the tooth is represented by dentin. The crown of the itch is covered with enamel, and the root of the tooth is covered with cement.
Dentin is a collagen that is highly saturated with mineral salts, mainly phosphate lime. This gives dentin extra strength with minimal brittleness. Dentin is permeated with a huge number of the finest tubules - up to 50 thousand per square millimeter of the surface. They work and ensure the growth, development, and vitality of the tooth cells - odontoblasts. The metabolism takes place in it quite intensively.
Enamel in the bulk consists of an inorganic substance. It is represented by enamel prisms, which are responsible for its special strength, and interprismatic substance. Enamel protects teeth from wear and tear. After damage, it does not recover. The defeat of the enamel is observed in dental caries, fluorosis.
The pulp is represented by blood vessels, lymphatic vessels, nerves, cells - odontoblasts. Odontoblasts form a layer on the surface of the dental cavity and with their numerous processes penetrate all dentin tubules, metabolism in the tooth is carried out. The pulp performs many functions, including trophic (nutritional), protective, regenerative, and regulatory. The abundance of blood vessels and nerves during the development of inflammation quickly leads to severe pain syndrome.
The cement covers the root of the tooth and is responsible for attaching the ligamentous apparatus to the tooth. Histologically, there are two types of cement: cellular (secondary) cement and acellular (primary). Cellular cement in composition and structure resembles a coarse-fibrous bone, contains cementocytes. It is usually located in the apical part of the root and the area of the root bifurcation. The acellular cement covers the rest of the root. It contains cementocytes and is composed of collagen fibers and an amorphous adhesive.
The blood supply to the tooth is carried out by branches extending from the external carotid artery. The most significant branches are the maxillary and lower alveolar arteries. The venous system follows the arterial system. The venous system of the teeth is closely related to the cerebral venous sinuses, therefore, dental diseases can cause complications in the form of vein thrombosis of the dura mater.
The innervation of the teeth is carried out mainly by the trigeminal nerve. The trigeminal nerve comes from three branches of this nerve - the maxillary, mandibular and ocular. Sympathetic and parasympathetic nerve fibers regulate blood circulation: when sympathetic nerve fibers release norepinephrine, vascular contraction occurs, and when acetylcholine is released by parasympathetic nerves, they expand.
The lymphatic vessels of the tooth ensure the outflow of lymph through the nearest lymph nodes, some of which are available for palpation, with the help of their examination it is possible to indirectly judge the presence of inflammatory diseases. For a more detailed diagnosis, methods of X-ray contrast studies of the lymphatic system are used.
There are temporary, replaceable, and permanent bites.
The temporary bite is represented by 20 milk teeth, which are fully manifested by 2 years. A changeable bite contains both milk and permanent teeth. The formation of the temporary ends with the eruption of the last milk tooth. During this period up to 6 years, when milk teeth begin to be replaced by permanent teeth, you should carefully monitor whether the child has bad habits (thumb sucking), whether breathing is disturbed, speech, whether the first milk teeth have fallen out too early. In the future, this can negatively affect the permanent bite.
The permanent bite includes 32 permanent teeth. Periods of an eruption of permanent teeth: central incisors 7-8 years, lateral incisors 8-9 years, canines 10-13 years, first premolars 9-10 years, second premolars 12-13 years, first molars 5-6 years, second molars 12- 13 years old, third molars 20-25 years old. A permanent bite is more stable, but it can still change as a result of abrasion of crowns, after the loss of individual teeth, or due to bad habits. Even in adulthood, they can lead to a change in the dentition, and, as a result, to a change in the permanent bite.
4 groups of teeth are distinguished by shape and function:
- Incisors are anterior teeth, four on each jaw. Their function is to bite off food. The root of the incisors is single, conical in shape. The root is longer than the crown.
- Fangs, two on each jaw, are needed to tear off food. The root of the canines is single. The root of the lower canine is shorter than that of the upper. There may be a bifurcation at the top, sometimes turning into a double root.
- There are four premolars on each jaw in a permanent bite, in the milk once they are absent. Serve for crushing, coarse grinding of food. They have one root, in some cases root bifurcation takes place. The crown is prismatic in the upper premolars, and the vestibular surface is convex in the lower ones.
- Molars with six teeth on each jaw in a permanent bite and four in a milk one. Designed for chopping and grinding food. They have two or three roots and a chewing surface, forming three, four, or five tubercles.
To describe the relief of the teeth and the localization of pathological processes, the following surfaces of the tooth crown are distinguished:
- The vestibular surface of the tooth, which faces the vestibule of the oral cavity (for the front teeth, this is the labial surface, for the back teeth, the buccal surface);
- The lingual surface of the tooth, facing the oral cavity (oral);
- The contact surface of the tooth (proximal), facing the adjacent teeth. The proximal surfaces of the teeth facing the center of the dentition (along the dental arch) are called medial (middle), and on the front teeth - medial, or medial. Surfaces directed in the opposite direction from the center of the dentition are called distal.
- The chewing surface of the tooth (in molars and premolars) is the surface of the tooth facing the opposite row of teeth or the incisal edge for incisors and canines. This surface is also called occlusal, or occlusal surface.