Lower jaw

The lower jaw (mandible) is the only movable bone of the skull. Read more about anatomy and function of the lower jaw!

Lower jaw

The horseshoe-shaped lower jaw (Mandible) is the largest facial bone and the only motile bone of the skull. The teeth are embedded in the middle horizontal part of the lower jaw. On the lateral, upwardly bent branches, the mandible sets with the temporomandibular joint on the temporal bone. Read everything important about the lower jaw: anatomy, function and important diseases!

What is the lower jaw?

The lower jaw bone consists of a body (Corpus mandibulae), whose rear ends on both sides in the jaw angle (Angulus mandibulae) in an ascending branch (Ramus mandibulae) go over. The angle between the body and the branch (angulus mandibulae) fluctuates between 90 and 140 degrees, depending on the strength of the masticatory apparatus - it reaches 150 degrees in newborns. It decreases with strong development of the masticatory muscles.

The basis of the mandible is the basal arch, which includes the base, the middle part of the branch and the articular process. The basal arch is slimmer towards the top, here sits on the alveolar arch, which carries the Zahnfรคcher the lower set of teeth. He is a little smaller and narrower than the basal arch and jumps back against the chin.

When teeth are missing, the alveolar arch changes its shape. With complete loss of teeth, it can even disappear completely, because a functionally unstressed bone is destroyed (inactivity atrophy). As a result, the lower jaw body appears narrower and lower, the mouth is "sunken" - if not restored by dentures the shape.

The outer surface of the lower jaw body

In the midline of the lower jaw, at the chin, there is a small bone border - the place where the two halves of the lower jaw are grown together after the embryonic period and ossified in the first year of life. Underneath, a bony triangle (Protuberantia mentalis) forms the lower boundary and two small cusps on either side of it form the lower corners of the triangle - the protruding chin.

At the level of the first to second molars, between the base and the alveolar margin lies the mental foramen, an exit point for nerves and vessels that lead from the canalis mandibulae to the skin.

A small elevation on the outer surface of the lower jaw body, the Linea obliqua, runs obliquely upwards to the Ramus (ascending branch of the lower jaw). Two muscles insert themselves into it: one pulls the corners of the mouth down, the other pulls the lower lip down and to the side.

Somewhat underneath, a muscle has its approach, which extends from the neck to the second rib and is counted among mimic muscles. Above, at the alveolar process and just below the molars, the muscle begins, with the corners of the mouth pulled to the side and lips and cheek pressed against the teeth. He helps suckle by stiffening the cheeks and urges the food between the teeth while chewing.

The inner surface of the lower jaw body

Near the bony ledge, where the two mandibular bones have grown together, are two small, strong bony prominences that serve as a reinforcement and as a point of attachment for two muscles - the muscle that sticks out the tongue and an oral floor muscle. Through this bony reinforcement of the lower jaw breaks in an impact always sideways of the chin area.

Beneath these bony prominences lies a pit for the insertion of the muscle, which is important for opening the mouth. Parallel to the course of the linea obliqua outside runs inside the lower jaw body, a line (linea mylohyoidea), attaches to the floor muscles. Above and below this line there are depressions in which the lower and the lower jaw glands lie.

The lower jaw carries the compartments for the tooth roots in the alveolar arch. The individual compartments are - as in the upper jaw - separated by bone septa, in teeth with multiple roots, the individual root fan bones are further divided. The bone of the alveolar process has a structure of fine trabeculae, which transfers the pressure created during chewing from the teeth to the jaws.

The lower jaw branches

The lower jaw branches are distinguished by two projections: the articular process and the ossified approach of the temporal muscle.

The articular process (condylar process) has a condyle and a neck. At the neck, the muscle sets in a pit, pulling the lower jaw forward and to the side. The condyle forms the temporomandibular joint in a pit of the temporal bone, together with an intervertebral disc (meniscus articularis).

The ossified approach of the temporal muscle (coronoid processus) is the second projection on each lower jaw branch. The temporal muscle pulls up the auricle and tenses the skull plate. Also, the muscle, which allows the oral closure and the advancement of the lower jaw, begins at the coronoid process.This extension is pointed in the adult pointed, curved backward in old age.

The lower jaw branches still have numerous indentations, incisions and roughnesses, which serve as average sites for nerves and vessels or attachment points for muscles.

What is the function of the lower jaw?

The lower jaw is the only movable bone of the skull. Through his movements against the upper jaw food bites are chewed and crushed. He also helps with the sound.

Movements of the lower jaw

The mandible can perform various movements: the mandible can be advanced (protrusion) and retracted (retrusion) in addition to opening and closing the mouth, sideways away from the midline and back to the midline.

Where is the lower jaw?

The lower jaw forms the lower part of the facial skull. Its two lateral branches are connected in the temporomandibular joint to the temporal bone.

What problems can the lower jaw cause?

A mandibular fracture may be accompanied by fractures of the tooth roots.

As a Progenie doctors refer to a jaw malposition in which the lower incisors bite over the upper. Those affected have a protruding chin.

In the case of the jaw clamp, the mouth can no longer be opened, and the jaw lock can no longer be closed. Possible causes include inflammatory processes (as in mumps), dislocation (dislocation) or fracture of the temporomandibular joint, scars or tumors.

The salivary glands in the lower jaw may be inflamed or malformed. In addition, tumors and metastases (secondary tumors of malignant tumors) can form here.

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