What is it?
Temporomandibular Joint Dysfunction, or TMD, is a classification of mechanical dysfunction involving the Temporomandibular Joint (TMJ). The TMJ is the joint that allows for open and closing of the jaw. The temporal bone is a part of the skull and remains stationary in this joint complex. The mandible bone, or the jawbone, does all the moving in this joint complex. The motion of this joint is rather unique in that it occurs in two stages: a rotary phase and a translative. The rotary phase is responsible for the first 20mm of mouth opening. In this phase, the condyle (end of the jaw bone) remains in the fossa (indent) of the temporal bone with no forward motion. To further open the mouth the condyle must slide forward out of the fossa.
How Does it Happen?
The most common cause for this limited or altered range of motion of this joint is due to the position of what is known as the articular disc. The articular disc is a piece or connective tissue that functions to allow for smooth motion of the mandible on the temporal bone particularly during the translation phase. The front of the disc is attached to a muscle that is in the mouth known as the lateral pterygoid. The back of the disc is attached to the retrodiscal tissue. If the disc is out of position it may momentarily or fully block the forward translation of condyle out of the fossa. Without this full forward translation, the mouth cannot open fully. Most people experience a click or pop as they open their mouth that may or may not cause pain.
This misalignment of the disc is most commonly caused by overuse or trauma. Foods that require a lot of heavy chewing place a lot of stress on the joint and the disc itself and should be avoided for those suffering from this condition. When the forward slide or translation is blocked there may be painful or pain-free clicking along with limited range of motion.
Physical therapists are in a unique position to help treat the condition. Typical treatment for this condition involves releasing restriction in cervical spine and masticatory musculature, mobilization of the TMJ, strengthening and stretching appropriate muscle groups, and education regarding the proper mechanics of the joints.