The human lower jaw (Latin mandibula) is an unpaired movable bone structure of the facial cranial region. It has a well-defined central horizontal part - the body (lat. basis mandibulae) and two processes (branches, lat. ramus mandibulae) extending at an angle upwards, extending along the edges of the body of the bone.
She takes part in the process of chewing food, speech articulation, forms the lower part of the face. Consider how the anatomical structure of the lower jaw correlates with the functions performed by this bone.
General plan of the structure of the mandibular bone
During ontogenesis, the structure of the human lower jaw changes not only in utero, but also postnatally - after birth. In a newborn, the body of the bone consists of two mirror halves connected semi-movably in the center. This middle line is called the mental symphysis (Latin symphysismentalis) and completely ossifies by the time the child reaches one year.
The halves of the lower jaw are arcuately curved, located with a bulge outward. If you outline along the perimeter, the lower border of the body - the base - is smooth, and the upper one has alveolar recesses, it is called the alveolar part. It contains the holes where the roots of the teeth are located.
The branches of the jaw are located by wide bone plates at an angle of over 90 ° C to the plane of the body of the bone. The place of transition of the body to the jaw branch is called the angle of the mandible (along the lower edge).
Relief of the outer surface of the body of the mandibular bone
From the side facing outward, the anatomical structure of the lower jaw is as follows:
- the central, forward-facing part is the chin protrusion of the bone (Latin protuberantia mentalis);
- mental tubercles rise symmetrically on the sides of the center (lat. tuberculi mentali);
- upwards obliquely from the tubercles (at the level of the second pair of premolars) are the mental foramina (Latin forameni mentali), through which the nerve and blood vessels pass;
- behind each hole begins an elongated convex oblique line (Latin linea obliqua), passing into the anterior border of the mandibular branch.
Such features of the structure of the lower jaw, as the size and morphology of the chin protrusion, the degree of curvature of the bone, form the lower part of the face oval. If the tubercles protrude strongly, this creates a characteristic relief of the chin with a dimple incenter.
In the photo: the lower jaw affects the shape of the face and the overall impression of it.
Posterior mandibular surface
From the inside, the relief of the mandibular bone (its body) is mainly due to the fixation of the muscles of the bottom of the oral cavity.
The following areas are distinguished on it:
- Chin spine (lat. spina mentalis) can be solid or bifurcated, located vertically on the central part of the body of the lower jaw. This is where the geniohyoid and genioglossus muscles begin.
- The digastric fossa (Latin fossa digastrica) is located at the lower edge of the mental spine, the place of attachment of the digastric muscle.
- The maxillary-hyoid line (Latin linea mylohyoidea) has the form of a mild roller, runs in the lateral direction from the mental spine to the branches in the middle of the body plate. The maxillary-pharyngeal part of the upper pharyngeal constrictor is fixed on it, and the maxillo-hyoid muscle begins.
- Above this line is an oblong sublingual fossa (lat. fovea sublingualis), and below and laterally - the submandibular fossa (lat. fovea submandibularis). These are traces of adherence of the salivary glands, sublingual and submandibular, respectively.
Alveolar surface
The upper third of the body of the jaw has thin walls that limit the dental alveoli. The border is the alveolar arch, which has elevations in the places of the alveoli.
The number of cavities corresponds to the number of teeth in the lower jawan adult, including the “wisdom teeth” that appear later than all, 8 on each side. The pits are septate, that is, they are separated from each other by thin-walled partitions. In the region of the alveolar arch, the bone forms protrusions corresponding to the expansion of the tooth sockets.
Relief of the surface of the branches of the lower jaw
The anatomy of the bone in the region of the branches is determined by the muscles attached to them and the movable joint connecting it to the temporal bones.
Outside, in the region of the mandibular angle, there is an area with an uneven surface, the so-called chewing tuberosity (Latin tuberositas masseterica), on which the masticatory muscle is fixed. Parallel to it, on the inner surface of the branches, there is a smaller pterygoid tuberosity (Latin tuberositas pterygoidea) - the place of attachment of the pterygoid medial muscle.
The opening of the lower jaw (lat. foramen mandibulae) opens on the central part of the inner surface of the mandibular branch. In front and medially, it is partially protected by an elevation - the mandibular uvula (Latin lingula mandibulae). The hole is connected by a canal passing in the thickness of the cancellous bone with the mental hole on the outside of the mandibular body.
Above the pterygoid tuberosity there is an elongated depression - the maxillo-hyoid groove (Latin sulcus mylohyoideus). In a living person, nerve bundles and blood vessels pass through it. This furrow can becomecanal, then it is partially or completely covered by the bone plate.
Along the front border of the inner side of the branches, starting just below the level of the opening of the lower jaw, descends and continues onto the body of the mandibular ridge (lat. torus mandibularis).
Mandibular bone processes
Two processes are well expressed at the ends of the branches:
- Coronoid process (lat. proc. coronoideus), anterior. On the inside, it has an area with a rough surface, which serves as an attachment site for the temporalis muscle.
- Condylar process (lat. proc. condylaris), posterior. Its upper part, the head of the lower jaw (lat. caput mandibulae) has an elliptical articular surface. Below the head is the neck of the mandible (lat. collum mandibulae), bearing on the inside a pterygoid fossa (lat. fovea pterygoidea), where the pterygoid lateral muscle is attached.
There is a deep recess between the processes - tenderloin (Latin incisura mandibulae).
Mandibular joint
The anatomy of the end sections of the branches of the lower jaw ensures its good mobility and articulation with the bones of the facial skull. Movements are possible not only in the vertical plane, the jaw also shifts back and forth and from side to side.
The temporomandibular joint is formed, respectively, by two bones: the temporal and lower jaw. The structure (anatomy) of this joint allows us to classify it as a complex cylindrical joint.
Mandibular articular fossa of the temporal bonecontacts with the anteroposterior portion of the head of the condylar process of the jaw. It is he who should be considered the true articular surface.
The cartilaginous meniscus inside the joint divides it into two "tiers". Above and below it there are gaps that do not communicate with each other. The main function of the cartilage lining is cushioning when grinding food with teeth.
Temporomandibular joint strengthened by four ligaments:
- temporomandibular (lat. ligatura laterale);
- main-maxillary (lat. ligatura spheno-mandibulare);
- pterygo-jaw (lat. ligatura pterygo-mandibulare);
- awl-jaw (lat. ligatura stylo-mandibulare).
The first of them is the main one, the rest have an auxiliary supporting function, since they do not directly cover the joint capsule.
How do the lower and upper jaws contact?
The anatomical structure of the teeth of the lower jaw is determined by the need for closure and contact with the upper row of teeth. Their specific location and interaction is called bite, which can be:
- normal or physiological;
- abnormal, caused by changes in the development of parts of the oral cavity;
- pathological, when the height of the dentition changes as a result of their abrasion, or the teeth fall out.
Changes in bite negatively affect the process of chewing food, provoke speech defects, deform the contour of the face.
Normally, the structure and relief of the surface of the mandibular row of teeth ensure their tight contact with the same maxillaryteeth. The mandibular incisors and canines are partially overlapped by similar upper teeth. External tubercles on the chewing surface of the lower molars fit into the pits of the upper.
Characteristic injuries
The lower jaw is not monolithic. The presence in it of channels, areas with different density of bone material causes typical injuries in injuries.
Common mandibular fracture sites are:
- The sockets of canines or premolars - small molars.
- The neck of the posterior (articular) process.
- Mandibular angle.
Since the bone is thickened in the region of the mental symphysis, and at the level of the 2nd and 3rd pairs of molars it is reinforced with an internal crest and an external oblique line, the lower jaw breaks in these places extremely rarely.
Another variant of damage, affecting not the bone itself, but the temporomandibular joint, is a dislocation. It can be provoked by a sharp movement to the side (from a blow, for example), an excessive opening of the mouth, or attempts to bite through something hard. In this case, the articular surfaces are displaced, which prevents normal movements in the joint.
The jaw should be set by a specialist traumatologist to prevent excessive stretching of the surrounding ligaments. The danger of this injury is that the dislocation can become habitual and recur with little impact on the jaw.
The mandibular joint experiences constant stress throughout a person's life. It is involved in receivingfood, conversation, is important in facial expressions. His condition can be affected by lifestyle, diet, the presence of a systemic disease of the musculoskeletal system. Prevention of injuries and early diagnosis of joint problems is the key to the normal functioning of the lower jaw throughout a person's life.
