The mandible, commonly known as the lower jawbone, is a singular bone that forms the lower framework of the face. It is the largest and strongest bone in the facial skeleton, providing structure to the chin and lower cheeks. This bone holds the entire lower row of teeth. The mandible is unique among skull bones due to its ability to move freely, which is essential for fundamental human actions.
Anatomical Position in the Skull
The mandible is situated inferiorly in the face, forming the lower boundary of the oral cavity beneath the maxilla (upper jaw). It is the only major bone of the skull, excluding the tiny middle ear ossicles, that possesses significant mobility. This mobility is facilitated by its bilateral articulation with the cranium at a pair of joints on either side of the head. The posterior ends of the mandible connect with the temporal bones of the skull, located just in front of the ears, to form the two temporomandibular joints (TMJ). The curved, superior edge of the bone, known as the alveolar border, contains the sockets that anchor the lower dental arcade.
Key Structural Features
The overall structure of the mandible is a symmetrical, horseshoe shape, consisting of a horizontal body and two vertical rami. The body is the curved anterior portion that holds the teeth and forms the chin. In the adult, the body represents the fused line of the two halves that developed during gestation, marked by a slight ridge at the center called the mandibular symphysis.
Rami and Processes
The two vertical rami project upward from the posterior ends of the body. The junction where the body and each ramus meet is the mandibular angle, which defines the lower corner of the jawline. Each ramus terminates in two distinct upward projections separated by a U-shaped mandibular notch. The anterior projection is the sharp coronoid process, which serves as an attachment point for the large temporalis muscle used in biting. The posterior projection is the condyloid process, featuring a rounded head (condyle). This condyle articulates with the temporal bone to form the TMJ. On the external surface of the body is the mental foramen, a small opening that allows the mental nerve and blood vessels to exit and supply sensation to the lower lip and chin.
Role in Movement and Function
The mandible’s unique ability to move comes from the Temporomandibular Joint (TMJ), a complex joint that permits both rotational and gliding motions. The condyle of the mandible fits into a depression in the temporal bone, separated by an articular disc that acts as a cushion. Since the right and left joints are connected by the single jawbone, they must operate in coordination.
The lower compartment of the TMJ allows for rotational, or hinge-like, movement that facilitates the initial opening and closing of the mouth. The upper compartment allows the condyle and disc to glide forward (translation), which is necessary for wide opening and protrusion of the jaw. The primary muscles of mastication, including the masseter, temporalis, and pterygoid muscles, control these actions with precision.
These complex movements enable the mandible to perform its primary functions: mastication and articulation. Mastication, or chewing, involves elevation (closing), depression (opening), and lateral excursion (side-to-side grinding) to process food. Articulation, or speech, relies on the fine, rapid movements of the jaw to modify the airflow and sounds produced by the vocal cords. The mandible’s mechanical strength and dynamic range are central to both nutrition and verbal communication.