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