Temporomandibular joint dysfunction: a theory based upon electromyographic studies of the lateral pterygoid muscle.

Electromyographic investigations into the function of the two individual heads of the lateral pterygoid muscle in normal persons are compared with patients suffering the pain of temporomandibular joint dysfunction and those with painless clicks. The results indicate that the lower head of the lateral pterygoid muscle, normally active only when depressing, protruding and deviating the mandible, becomes active on closing and clenching in patients suffering pain. Patients with painless clicks behave as normals. These results are discussed and a theory is presented which suggests that temporomandibular joint dysfunction has a simple pathological basis.