Temporomandibular joint connects your lower jaw to the temporal bones of your skull, which are in front of each ear. It facilitates movement of your jaw, so you can talk, chew, and yawn. Temporomandibular joint and muscle disorders, commonly called "TMJ," are a group of conditions that cause pain and dysfunction in the jaw joint and the muscles that control jaw movement. The exact reason for TMJ is not known. Dentists believe symptoms arise from problems with the muscles of your jaw or with the parts of the joint itself.