The normal TMJ

The temporomandibular joint (TMJ) is the articulation, or joint between the cup- shaped depression in the temporal bone of the skull (called the articular fossa) and knob-like projection of the lower jaw called the condylar head.  The two bones are separated by a fibrous disc called the meniscus. The disc is normally held in position by the anterior (forward) band and a posterior band tissue attachments. This joint complex is surrounded by a joint capsule that is lined with special tissue called synovial membrane.

Normal TMJ function

The right and left TMJ’s work “independently together” to allow the u-shaped lower jaw to function in a wide range of motions. The jaw joints have a hinge function, where the jaw opens and the condylar heads rotate and stay in the articular fossae.  For wider jaw opening or wide side to side motions, the right and left condylar heads of the mandibles can slide together or independently down the ramp shaped portion of the joint called the articular eminence. The disc normally will remain between the two bones and acts as a cushion between them as the lower jaw moves. The lower jaw bone is movement is controlled by muscles of the head and face called the “muscles of mastication”

Does your jaw click and pop and hurt when you chew or yawn? Does your jaw ever get stuck?

This could mean that the meniscus, or disc is slipping, usually forward, as the condylar head starts to rotate in the fossa or slides along the articular eminences. This causes the condylar head to press on the posterior band attachment. Often the disc will resume its position when the jaw closes. This is called anterior displacement with reduction. When the disc slips out of position, this can result in joint noises, inflammation and pain, and difficulty chewing and opening the jaw.

Sometimes the disc is displaced forward and does not return into a normal position. This is called anterior displacement without reduction. Patients with anterior displacement without reduction often are unable to open the mouth fully, or need to move the jaw side to side to get it “unstuck” before being able to fully open. This can lead to pain, inflammation and discomfort.

There are other conditions that can cause TMJ pain too

Sometimes there is a tear in the meniscus, and a patient will note a grinding sound when they move their jaw. Osteoarthritis, the so-called “wear and tear arthritis”, and rheumatoid arthritis can affect the TMJ’s. These are typically painful conditions and can lead to degeneration of the bony parts of the TMJ and loss of function, and changes in the patient’s bite.

Oral habits, such as tooth grinding, jaw muscle clenching, nail biting, and so on can create TMJ pain or make TMJ pain worse. Sometimes these habits can cause  spasm and pain in the muscles of mastication