The temporomandibular joint (TMJ), also known as the gynglymoarthrodial joint (diarthrosis - freely movable joint), is paired joint between the squamous part of the temporal bone and the ramus of the mandible. Therefore it is a connection between the lower jaw and the skull. As the TMJ is involved in the wide range of movements of the lower jaw and, therefore, participates in the digestion process, it is also associated with teeth.

The joint is located on the lateral part of the face - anterior to the auricle and tragus of the ear.

Several structures articulate in the joint, and they are:

• Condyle (head of the mandible)

• Mandibular (glenoid) fossa of the temporal bone

• Articular eminence (tubercle) of the temporal bone

• Articular disc

This joint is unique as the articulating structures actually do not articulate because they are separated by an articular disc.

The articular disc is a biconcave plate located within the joint cavity between the articular surfaces of both articulating anatomical structures (mandibular condyle and temporal bone). Its outer border is fused with the joint capsule, and it divides the joint cavity into two smaller joint cavities known as the floors or compartments (superior and inferior). Therefore the TMJ is a compound joint.

The articular disc is made of dense fibrous connective tissue and contains three discrete zones, named the anterior, posterior, and intermediate zones. The center of the disc is avascular and also does not contain any nerve tissue. But instead the disc receives neurovascular supply from the periphery, more precisely from the area known as the retrodiscal pad. The retrodiscal pad or bilaminar zone contains loose connective tissue rich in blood vessels and nerve tissue. This area binds the articular disc to the condyle of the mandible and temporal bone by fibers known as the superior and inferior lamina. The retrodiscal pad helps to prevent posterior dislocation of the joint.

The superior floor of the TMJ is limited by the temporal bone and the articular disc (disco-temporal), while the inferior floor is limited by the articular disc and mandible (disco-mandibular).

The inferior compartment is slightly smaller than the superior one. Both contain synovial fluid. The articular surfaces are covered by fibrocartilage, not hyaline cartilage, like it is in other joints.

The upper floor is a plain-gliding joint responsible for translational movements, while the lower is a hinge joint for rotational movements discussed later in the next slides.