Lower jaw (mandibula) - mobile unpaired horseshoe-shaped bone. It consists of two symmetrical halves, each of which has a body and branch. The body of the mandible is presented ground and alveolar part. Body height in the jaw incisors more in the third molars - is considerably less. Its thickness is greatest in the area of molars, the lowest - at the level of small teeth. In the anterior region of the outer surface of the body has a chin mound. Accordingly, the tops of the molars are small chin holes are places where mandibular canal. From the front edge of the branches to the level of the sixth to fifth tooth is vestibular bone shaft - a slash line (linia obligna). On the inside the chin department is bone protrusion - chin beard, below from her and lateral - digastric fossa. On the inner side of the body of the mandible is mandibulohyoid line - the same name by attaching the muscles, the superior constrictor of the pharynx, chin-hyoid muscles. Below this line and parallel to it is the same name furrow for vessels and nerves.
Alveolar part of the body of the mandible has to 8 lunochek teeth on each side. The wells are separated from each other mezhalveolyarnymi partitions. On the outer surface of the alveolar part of the lune correspond alveolar eminence. The shape, depth and width lunochek, their wall thickness for different groups of teeth are different. More profound is the lune canine and second premolar. The third molars lingual part of the lune is much thinner than the vestibular. Behind him is pozadimolyarnaya fossa. The body of the mandible consists of outer and inner compact discs and concluded between the spongy substance. The thickness of compact discs in the base is slightly lower than in the alveolar part, where the spongy substance and more. In the area of the base thickness of the outer compact disc is less than the thickness of the inner. In the alveolar part of these relationships are inverse: the outer compact disc thicker than the inner. Most thickened lower edge of the zone of the central incisors.
In the thicker body of the mandible passes mandibular canal, which are nizhnealveolyarny nerve, artery, and Vienna. It begins mandibular opening on the inside of the branches and ends chin hole on the outer surface of the body of the mandible. The channel closest to the bottom of the third molars lune (1,5-2,5 mm) and more distant from the bottom of the sixth alveola tooth (7-8 mm), ie He has an arched shape, convexity downwards. Often, the channel passes through the hole of the third molar. In the zone of large molars channel is located closer to the inner compact disc, and in the premolars closer adjoins to the outside of a compact plate. Sometimes the spongy substance between the inner and outer compact disc at the level of the channel for it. In this case, the walls of his concern of compact discs.
In the branches of the lower jaw distinguish between outer and inner surfaces, front and rear edge, coronal and condylar processes. The front edge of the branches of lateral moves in a diagonal line, medial spread to lune third molars, limiting pozadimolyarnuyu hole. Up the front edge turns into coronary process, which is attached to the temporalis muscle. Backward from its location condylar processus. These processes form a clipping of the mandible. Condylar processus has a ground neck and head to the articular surface, which is flattened. On the inner side of the condylar neck of the appendix has webbed fossa; are attached webbed outer muscle. On the outer surface of the branch is chewing tuberosity, which extends to the outer surface of the angle of the jaw. To it is attached masseter. The inner surface of the branches and the angle of the mandible is webbed tuberosity, to which is attached medial webbed muscle. In the middle of the inner surface of the mandibular branch has a hole, covered front and top of the bone projection (tongue). Above and in front of the uvula situated mandibular ridge - a place of attachment of jaw-jaw and pterygium-stnoklinovidnoy ligaments. Outer branch of the compact disc inside the jaw is thinner all over. Spongy substance in larger amounts contained in the head, neck in condylar process and in the transition region of the body in the branch; little spongy substance in the coronoid process.
The smallest cross-sectional area of the mandible, in the middle of the condylar neck of the appendix, the angle of the branches of the mandible, the first premolar. Compact discs of the lower jaw can withstand the compressive load on the attachment of chewing muscles more than 5 kg/mm2, the temporalis muscle - more than 10 kg/mm2, in places, free from attachment of muscles - more than 16 kg/mm2. At the bottom of the body of the mandible bone plate holes are directed away from the teeth to the bottom of the jaw with an inclination toward the corner. Bone beams bent on body height with convexity facing anteriorly. As part of the alveolar bone is dominated by direct beam having a direction along the length of the jaw. The thickness of the condylar neck of the appendix in the anteroposterior direction is much smaller than in the lateral direction. In the base condylar sprouts its thickness in the anteroposterior direction is much greater than in the side. It is these relationships would result from typical arrangement places the fracture when struck on the chin or lateral parts of the body of the mandible.
To attach the lower jaw muscles, raising (posterior group) and let it drop (front group). The function of these muscles largely determines the nature of the displacement of fragments of lower jaw when it's turn.
