The mandible is the lower jawbone, the largest and strongest bone of the human face. As the only mobile bone in the skull, aside from the small bones of the middle ear, its movement is necessary for daily activities. It forms the foundation of the lower face, holds the lower teeth, and works in opposition to the fixed upper jaw, or maxilla.
Anatomy of the Mandible
The mandible has a distinctive U-shape formed by a horizontal body and two vertical extensions called rami. The body of the mandible is the curved, horizontal portion that anchors the lower set of teeth. On the external surface of the body, near the midline, is a faint ridge known as the mandibular symphysis, which marks the fusion of the two halves of the bone that occurs shortly after birth.
Each ramus ascends from the posterior aspect of the body, creating the mandibular angle where the body and ramus meet. At the top of each ramus, there are two projections. The posterior one is the condylar process, a rounded knob that fits into a fossa of the temporal bone of the skull to form the temporomandibular joint (TMJ), which allows the jaw to move.
Anterior to the condylar process is the coronoid process, a triangular projection. This site serves as an attachment point for the temporalis muscle, a muscle involved in chewing. The mental foramen is a small opening on the external surface of the body, below the second premolar tooth. This foramen allows nerves and blood vessels to pass from within the jaw to supply the tissues of the lower lip and chin.
Functions of the Mandible
The primary role of the mandible is mastication, or the chewing of food. Powerful muscles, including the masseter and temporalis, attach to the mandible and enable it to move up, down, and side-to-side. This range of motion allows for the effective grinding and crushing of food between the upper and lower teeth, preparing it for digestion.
Beyond chewing, the mandible is also involved in speech articulation. The movement of the lower jaw helps to change the size and shape of the oral cavity. These adjustments produce the sounds required for communication.
The mandible also serves a structural purpose for the lower face. The bone’s shape defines the contour of the chin and lower face.
Common Mandibular Conditions
Due to its prominent position and function, the mandible is susceptible to several conditions. Fractures are a common injury, often resulting from direct trauma to the face from accidents or violence. The condylar process is one of the most frequent sites for such breaks.
Mandibular dislocation can occur when the condylar process slips out of its joint with the temporal bone. This can happen from opening the mouth too wide, such as during yawning, or from an impact. The jaw becomes “locked” in an open position, causing discomfort and requiring medical intervention to reposition.
Temporomandibular joint (TMJ) disorders cause pain and dysfunction in the jaw joint and its associated muscles. These conditions can arise from factors like arthritis, injury, or inflammation of the muscles and ligaments. Symptoms often include jaw pain, headaches, earaches, and difficulty with jaw movement.