Mandible

Mandibula

Also known as: lower jaw, jawbone

The largest and strongest facial bone and the only movable bone of the skull (apart from the ossicles). It carries the lower teeth and articulates with both temporal bones at the temporomandibular joints.

Overview

The mandible consists of a horseshoe-shaped body and two vertical rami meeting it at the angles. The body has an upper alveolar part holding the lower teeth and a lower base. In the midline anteriorly, the mental protuberance marks the former mandibular symphysis (the two halves fuse by the end of the first year). On the internal surface are the mental spines (genial tubercles) for genioglossus and geniohyoid, the digastric fossae, the mylohyoid line (separating the sublingual fossa above from the submandibular fossa below). The mental foramen lies below the second premolar and transmits the mental nerve and vessels.

Each ramus ends above in two processes separated by the mandibular notch: the anterior coronoid process (insertion of temporalis) and the posterior condylar process, comprising the head (condyle), which articulates with the temporal bone, and the neck, whose pterygoid fovea receives the lateral pterygoid. On the medial surface of the ramus, the mandibular foramen, guarded by the lingula (attachment of the sphenomandibular ligament), leads into the mandibular canal carrying the inferior alveolar nerve and vessels to the teeth. Masseter and medial pterygoid insert on the outer and inner aspects of the angle respectively, forming a muscular sling.

Location

Lower face; forms the lower jaw and chin.

Parts & subdivisions

Body

Horizontal part with the alveolar process and the base.

Ramus

Vertical part on each side; masseter laterally, medial pterygoid medially.

Angle (gonion)

Junction of body and ramus — a common fracture site.

Condylar process

Head articulates with the mandibular fossa; neck receives the lateral pterygoid.

Coronoid process

Insertion of temporalis.

Mandibular foramen and lingula

Entry of the inferior alveolar nerve (V3) and vessels; target for the inferior alveolar nerve block.

Mental foramen

Below the 2nd premolar; mental nerve and vessels to the chin and lower lip.

Mylohyoid line

Origin of mylohyoid (floor of the mouth).

Mental spines (genial tubercles)

Origins of genioglossus (upper) and geniohyoid (lower).

Alveolar part

Sockets for the 16 lower permanent teeth.

Anatomy

Innervation

Inferior alveolar nerve (V3) to bone and lower teeth; mental nerve to the skin of the chin and lower lip.

Arterial supply

Inferior alveolar artery (from the maxillary artery) and periosteal branches of the facial artery.

Articulations

Temporal bones at the temporomandibular joints (bilateral synovial joints); teeth in sockets (gomphoses).

Ligaments

Lateral (temporomandibular) ligament, sphenomandibular ligament (to the lingula), stylomandibular ligament (to the angle).

Ossification

Mostly intramembranous, beginning ≈week 6–7 lateral to Meckel cartilage (1st pharyngeal arch); secondary cartilages form the condyle (a growth site until early adulthood) and coronoid process.

Clinical significance

Mandibular fractures

Because the mandible and cranial base form a ring, fractures are often bilateral — e.g. a blow to the chin fracturing the parasymphysis plus the contralateral condylar neck. Common sites: condyle, angle (especially through an impacted third molar), body. Damage to the inferior alveolar nerve causes lower-lip numbness.

TMJ dislocation

Anterior dislocation when the condyle slides in front of the articular tubercle on wide yawning; reduced by pressing down and back on the molars.