Temporo-Mandibular Articulation

This joint (Articulatio mandibularis) is the only diarthrosis formed between bones of the skull.

The articular surfaces are dissimilar in form and size. That on the squamous temporal bone is concavo-convex, and the long axis is directed outward and somewhat forward; it consists of a glenoid cavity, which is continued upon the postglenoid process behind, and a condyle in front. The mandible presents a transversely elongated condyle.

The articular disc is placed between the joint surfaces, which it renders congruent. Its upper and lower surfaces are molded upon the temporal and mandibular surfaces respectively, and its circumference is attached to the joint capsule; thus it divides the joint cavity into upper and lower compartments, the former being the more roomy.

The joint capsule is strong and tight. It is reinforced by two ligaments. The external ligament (Ligamentum laterale) extends obliquely across the anterior part of the outer surface of the capsule, from which it is not distinctly separable. The posterior ligament (Ligamentum posterius) is an elastic band which is attached above to the postglenoid process, and below to a line on the posterior face of the neck of the mandible.

Movements.—The chief movements take place around a transverse axis passing through both joints. Associated with this hinge-like action is slight gliding movement, as in opening and shutting the mouth. When the mouth is shut, the condyle lies under the glenoid cavity. When the mandible is depressed, the condyle moves forward under the articular eminence of the temporal bone, carrying the disc with it. In protrusion and retraction of the lower jaw the gliding movement just described occurs without the hinge-like rotation of the condyle. These movements are similar in both joints. In the lateral movements (as usually performed in mastication) the action consists of rotation of the condyles around a vertical axis, while the disc glides forward on one side and backward on the other.