Figure 1. Temporomandibular Joint.
The temporalis and the masseter muscles are the primary muscles used when eating or clenching the teeth and are the strongest among the muscles of mastication. TMD pain is primarily associated with pain in these muscles. The medial pterygoid muscles is also used to close the mandible, while the lateral pterygoid muscle pulls the mandible forward.
As is true for other muscles, the characteristics of jaw muscles can change in response to how they are used or overused. Exercise or lack of exercise and changes in patterns of use will affect the structure of these muscles as well as influence whether they perform their functions smoothly and whether these functions are accompanied by pain and discomfort. Jaw muscles that are overused (for example, through excessive muscle tension, clenching and bruxism) may feel tender, achy or “tight.” On the other hand, stretching and strengthening the muscles through controlled exercise can lead to increased flexibility and decreased discomfort.
TMJ and Associated Structures
The TMJ is like a sliding “ball and socket” joint that allows smooth movement of the mandible during function. As the jaw opens, the condyle (the “ball”) rotates and glides along the glenoid fossa (the joint “socket”), and then slides back to its original position when the mouth closes.
To keep the jaw opening and closing motions smooth, a soft articular disc composed of cartilage lies between the condyle and the fossa. The articular disc acts as a pad or cushion for the TMJ during chewing and other movements. The joint contains synovial fluid, that keeps the TMJ well lubricated and nourished. The bony surfaces of the TMJ are covered by fibrocartilage that can repair or regenerate even after it has been damaged by disease or jaw injury. Sensory innervation comes from the mandibular branch of the trigeminal nerve.