Temporomandibular Joints (TMJ)

Temporomandibular Joints

Each temporomandibular joint (TMJ) in the jaw is a modified hinge joint. Lying just anterior to the ear, the condylar process of the mandible is articulated with the inferior surface of the squamous area of the temporal bone. The condylar process is shaped like an egg. The articular sur-face of the temporal­ bone, however, has a more complicated shape. ­Anteriorly, it forms the dense

knoblike structure­ known as the articular tubercle. Posteriorly, it forms the concave-shaped mandib-ular fossa. The lateral­ aspect of the loose articular ­capsule encloses the TMJ and thickens to form the lateral­ ligament. Inside the capsule,­ the articular disc divides the synovial cavity into superior and inferiorsections.

The (TMJ) allows two types of movement. Its concave inferior disc surface receives the mandible’s condylar process. This allows the hinge-like move-ment of depressing and elevating the mandible as the mouth is opened and closed. The second type of movement occurs as the superior disc surface glides anteriorly with the condylar process as the mouth is widely opened. This anterior movement braces the condylar process against the articular tubercle. Therefore, the mandible cannot move through the thin “roof ” of the mandibular fossa when biting is required of hard foods. The superior section allows the joint to glide from side to side. When grinding motions occur, the posterior teeth are drawn into occlusion, and the mandible moves side to side, a movement known as lateral excursion. This lateral movement of the jaw only occurs in humans and other mammals.