There is a cartilaginous disc between the two bones to act as a bearing. This disc has no blood supply and so is nourished by the slick synovial fluid which aids in the smooth movement. The back of the disc is tethered to the back of the joint with a soft band of retro-discal tissue that has blood and nerve supply. The front part of the disc is connected to a small muscle (called Lateral Pterygoid muscle) that pulls it forward during opening of the jaw. The discal ligaments hold the disc tied down to the head of the condyle.
If there is trauma (either acutely from a blow or chronically from clenching) to the discal ligament that leads to a tear, then the disc would slip out from between the two bones. This dislocation is usually Anterior (to the front). As the jaw is opened to a certain amount, the tether holding it to the back of the joint makes the disc jump on to the top of the condyle – where it belongs. This leads to a clicking or popping noise.
In rare cases, the disc would stay in front of the condyle and so would not allow the jaw to be opened very far. Such a condition is called a closed lock of the TM Joint.
But as the jaw closes, the disc slips out – usually without much noise. So the joint now has the soft retro-discal tissue between the bones instead of the disc. Since this tissue has blood supply, it can lead to inflammation. If this tissue is perforated, then there is bone to bone contact during function. The joint surfaces get rough leading to a grinding noise. Arthritis of the TM Joint can lead to destruction of the bony surfaces.
It is easier to tolerate and minimize the use of other joints in the body afflicted by arthritis. But the TM Joints are in use every time we eat, speak and swallow 2000 to 3000 times a day. So arthritis of TM Joints really impacts the quality of one’s life.
A clicking and popping TM Joint may lead to irreversible damage to the joints. It is best to correct them at an earlier stage than later.