The temporomandibular joint combines a hinge action with sliding motions. The parts of the bones that interact in the joint are covered with cartilage and are separated by a small shock-absorbing disk, which normally keeps the movement smooth.
Painful TMJ disorders can occur if:
• The disk erodes or moves out of its proper alignment
•The joint's cartilage is damaged by arthritis
•The joint is damaged by a blow or other impact
In many cases, however, the cause of TMJ disorders isn't clear.
Risk factors:
Factors that may increase the risk of developing TMJ disorders include:
•Various types of arthritis, such as rheumatoid arthritis and osteoarthritis
•Jaw injury
•Long-term (chronic) grinding or clenching of teeth
•Certain connective tissue diseases that cause problems that may affect the temporomandibular joint
Courtesy: Mayo Clinic