The mandibular bone, commonly known as the lower jaw, is the largest and strongest bone within the facial skeleton. It is also the only freely movable bone of the skull, aside from the tiny bones in the middle ear. This bone features a characteristic U-shape, providing the lower face and chin with their defining structure.
Anatomy of the Mandible
The mandible consists of a horizontal body and two vertical rami that project upwards. The body forms the curved front portion, supporting the lower arch of teeth. Small openings on the front of the body, mental foramina, allow nerves and blood vessels to pass through, supplying sensation to the lower lip and chin.
Two vertical rami extend upward from the back of the body, connecting at the mandibular angle. Each ramus features two upper projections: the condylar process, a rounded knob forming part of the temporomandibular joint, and the coronoid process, a triangular projection serving as an attachment point for a major chewing muscle.
Primary Functions
The mandible’s primary function is mastication, or chewing food. Its controlled movements efficiently break down food particles, preparing them for swallowing through up-and-down and side-to-side motions against the upper teeth.
Movement of the lower jaw also contributes to speech and articulation, helping form various sounds for clear communication. Beyond these roles, the mandible provides structural support, housing the lower set of teeth.
The Temporomandibular Joint
The temporomandibular joint (TMJ) is a complex synovial joint that connects the condylar process of the mandible to the temporal bone of the skull on each side of the head. This articulation allows for hinge-like and sliding movements, enabling the jaw to open, close, move side to side, and shift forward and backward.
Muscles of mastication, such as the masseter and temporalis, attach to the mandible, powering its movements. The temporalis muscle attaches to the coronoid process, while the masseter muscle connects to the ramus. These muscles provide the force and control for jaw function.
Common Mandibular Conditions
The mandible, despite its strength, is susceptible to various conditions. Fractures are common, often from trauma, with the condyle being a frequently affected area. A dislocation occurs when the condylar process slips out of its socket in the temporal bone, preventing the mouth from closing.
Temporomandibular Disorders (TMD) cause pain and dysfunction in the jaw joint and its associated muscles. Symptoms include jaw tenderness, facial pain, headaches, and restricted jaw mobility. Bone resorption, a process of bone loss, can occur in the jaw after teeth are extracted, particularly due to the lack of supporting structures.