Lower jaw

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The horseshoe-shaped lower jaw (mandible) is the largest facial bone and the only movable bone in the skull. The teeth are embedded in the central, horizontal part of the lower jaw. The mandible and the temporomandibular joint are attached to the temporal bone on the lateral, upwardly curved branches. Read everything you need to know about the lower jaw: anatomy, function and major diseases!

What is the lower jaw

The lower jaw bone consists of a body (corpus mandibulae), the rear ends of which merge into an ascending branch (ramus mandibulae) on both sides at the angle of the jaw (angulus mandibulae). The angle between the body and the branch (angulus mandibulae) varies between 90 and 140 degrees, depending on the strength of the chewing apparatus - in newborns it reaches 150 degrees. It decreases with strong development of the masticatory muscles.

The basis of the mandible is the basal arch, which includes the base, middle part of the branch, and the articular process. The basal arch becomes slimmer towards the top; this is where the alveolar arch sits, which carries the tooth sockets of the lower row of teeth. It is slightly smaller and narrower than the basal arch and jumps back in relation to the chin.

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

The outer surface of the lower jaw body

In the middle line of the lower jaw, on the protrusion of the chin, there is a small bone ridge - the place where the two halves of the bone of the lower jaw have grown together after the embryonic period and ossified in the first year of life. Below that, a bone triangle (Protuberantia mentalis) forms the lower boundary and two small bumps on either side form the lower angles of the triangle - the protruding chin.

At the level of the first to second molar, between the base and the alveolar margin, lies the mental foramen, an exit point for nerves and vessels that lead from the mandible canal 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 use it: one pulls the corners of the mouth down, the other pulls the lower lip down and to the side.

A little below this is a muscle that extends from the neck to the second rib and is counted as part of the mimic muscles. Above this, on the alveolar process and directly under the molars, the muscle attaches, with which the corners of the mouth can be pulled to the side and the lips and cheek pressed against the teeth. It helps with sucking by stiffening the cheeks and forcing the food between the teeth while chewing.

The inner surface of the lower jaw body

Near the bone ridge, where the two lower jaw bones have grown together, there are two small, strong bony protrusions that serve to strengthen and attach two muscles - the muscle that sticks out the tongue and a muscle of the floor of the mouth. Due to this bony reinforcement, the lower jaw always breaks laterally from the chin area in the event of an impact.

Underneath these protruding bones there is a pit for the insertion of the muscle, which is important for opening the mouth. A line (Linea mylohyoidea), to which the oral floor muscle attaches, runs parallel to the course of the outer oblique line on the inside of the lower jaw body. Above and below this line there are depressions in which the sublingual and submaxillary glands lie.

The lower jaw carries the compartments for the tooth roots in the alveolar arch. As with the upper jaw, the individual compartments are separated by bone septa; in the case of teeth with multiple roots, the individual root compartments are further subdivided into bones. The bone of the alveolar processes has a structure of fine trabeculae, which means that the pressure that occurs when chewing is transferred from the teeth to the jaws.

The lower jaw branches

A distinction is made between two protrusions on the branches of the lower jaw: the articular process and the ossified attachment of the temporal muscle.

The articular process (processus condylaris) has a joint head and a neck. The muscle that pulls the lower jaw forward and sideways is attached to the neck in a pit. The joint head forms the temporomandibular joint in a pit in the temporal bone, together with an intervening joint disc (meniscus articularis).

The ossified attachment of the temporal muscle (coronoid process) is the second protrusion on each branch of the lower jaw. The temporal muscle pulls the auricle up and tightens the skull plate. The muscle that enables the mouth to close and the lower jaw to be pushed forward also attaches to the coronoid process. This process is pointed in the adult and curved backwards in old age.

The branches of the lower jaw still have numerous depressions, incisions and roughness, which serve as intersections for nerves and vessels or at the attachment points for muscles.

What is the function of the lower jaw?

The lower jaw is the only movable bone in the skull. Bites of food are chewed and crushed by its movements against the upper jaw. He also helps with the formation of sounds.

Movements of the lower jaw

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

Where is the lower jaw located?

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

What problems can the lower jaw cause?

A lower jaw fracture can be accompanied by fractures of the tooth roots.

Doctors refer to a misaligned jaw as a progeny, in which the lower incisors bite over the upper ones. Those affected have a protruding chin.

With the jaw clamp, the mouth can no longer be opened, with the jaw lock it can no longer be closed. Possible causes are inflammatory processes (as with mumps), a dislocation (dislocation) or a fracture of the temporomandibular joint, scars or tumors.

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

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