The mandible

The mandible articulates through its head with the articular process of the temporal bone. The bone is flattened as the ramus and changes direction at the angle. On its inside surface the mandible has a foramen for the inferior alveolar nerve and vessels. The mandibular foramen is partly covered over by a spike of bone, the lingula. As the inferior alveolar nerve enters the mandibular foramen it gives off a motor nerve to mylohyoid and the anterior belly of digastric. This nerve lies in a shallow groove in the bone. Anteriorly on the external surface lies the mental foramen. The terminal branches of the inferior alveolar nerve emerge to supply the skin as the mental nerve.

TMJ and movement

The mandible articulates with the temporal bone at the temporomandibular joint (TMJ). Movements possible at this joint include depression and elevation of the mandible, protraction and retraction, and side to side movements. The joint has an intra-articular disc. As the jaw is opened the head of the mandible and the disc are pulled forwards onto the articular tubercle.

The mandible can be dislocated or fractured. The mandible is most commonly dislocated in an anterior direction, with the head of the mandible passing over the articular tubercle. The mandible may be fractured anterior to the masseter muscle. Fracture will result in injury to the inferior alveolar nerve and vessels. Normal action of the mandible in chewing is produced by the muscles of mastication. The temporalis muscle fills the temporal fossa on the side of the skull and inserts onto the coronoid process and anterior edge of the ramus of the mandible. It elevates and retracts the mandible. The masseter muscle arises from the inside of the zygomatic arch and inserts into the lower edge of the body of the mandible at the angle. It elevates the jaw. The medial pterygoid muscles arises from the medial side of the lateral pterygoid plate to insert on the medial side of the angle of the mandible, forming a sling together with masseter. The lateral pterygoid muscle arises from the lateral side of the pterygoid plate and neighbouring maxilla to insert into the capsule and disc of the TMJ and the neck of the mandible. It protracts the jaw, and unilaterally moves the jaw from side to side. The mandibular division of the trigeminal nerve supplies all these muscles.