Temporomandibular Joint Disorder (TMJ) is a condition that may be suffered by more than 30 million Americans. Sometimes called "the Great Imposter" for its ability to masquerade as other conditions, TMJ can result in symptoms as diverse as sleep disorders, facial pain, back pain, tooth pain, ringing in the ears, and tingling or numbness in the extremities.

The temporomandibular joints are located on either side of the head, where the jaw (mandible) meets the skull. In itself it is composed of three parts, the articulating surface on the skull, described as a fossa, the articulating surface on the mandible, described as a condyle, and the disc of cartilage that acts as a cushion between them. TMJ can be caused by a condition in the joint itself, in which case it is described as being intracapsular, or by conditions outside the joint, in which case it is described as being extracapsular.

Intracapsular TMJ

Intracapsular TMJ is the result of some structural change in one of the three components and/or their relationship with one another. They can interfere with the function of the jaw and often produce pain, especially localized pain that is often easily traceable to jaw motion, although the actual diagnosis of TMJ can still be very difficult. There are four commonly recognized types of intracapsular TMJ.

Developmental disorders can lead to an abnormal development of the joint. These often appear in patients of a relatively young age and tend to be highly symptomatic.

Diseases such as degenerative arthritis, rheumatoid arthritis, and neoplasms (pre-cancerous growths) can attack the joint. Although neoplasms can be isolated, arthritic TMJ often develops along with other affected joints. These tend to appear in older patients.

Injuries can often lead to displacement of the joint. Although the trauma does not need to be directly to the jaw, the sudden onset of this type of TMJ makes it easy to trace back to its cause.

Internal derangements are TMJs that set in without any evidence of external influence. Instead, the relationship between the condyle, fossa, and disc is disrupted for no apparent reason.

Extracapsular TMJ

Extracapsular TMJ is caused not by damage to the joint itself, but by conditions outside the joint that exert displacing force on the joint. The most common cause of extracapsular TMJ is malocclusion, when teeth don't fit together properly. Malocclusion can be congenital--related to poor dental development--or it can be the result of tooth loss, poor dental restorations, or dental trauma. Because this kind of extracapsular force places constant strain on the muscles and may displace or adversely affect important nerves in the area, extracapsular TMJ is more likely to create wide-ranging effects, such as headaches, ear pain, facial pain, and tooth wear and pain among other effects.