Definition of TMJ disorders:

Temporomandibular joint and muscle disorders (TMJ disorders) are problems or symptoms of the chewing muscles and joints that connect your lower jaw to your skull.

See also: Facial pain

Causes, incidence, and risk factors:

There are two matching temporomandibular joints -- one on each side of your head, located just in front of your ears. The abbreviation "TMJ" literally refers to the joint but is often used to mean any disorders or symptoms of this region.

Many TMJ-related symptoms are caused by the effects of physical stress on the structures around the joint. These structures include:

• Cartilage disk at the joint
• Muscles of the jaw, face, and neck
• Nearby ligaments, blood vessels, and nerves
• Teeth

For many people with temporomandibular joint disorders, the cause is unknown. Some causes given for this condition are not well proven. These included:

• A bad bite or orthodontic braces
• Stress and tooth grinding. Many people with TMJ problems do not grind their teeth, and many who have been grinding their teeth for a long time do not have problems with their TMJ joint. For some people, the stress associated with this disorder may be caused by the pain as opposed to being the cause of the problem.

Poor posture can also be an important factor in TMJ symptoms. For example, holding the head forward while looking at a computer all day strains the muscles of the face and neck.

Other factors that might make TMJ symptoms worse are stress, poor diet, and lack of sleep.

Many people end up having "trigger points" -- contracted muscles in your jaw, head, and neck. Trigger points can refer pain to other areas, causing a headache, earache, or toothache.

Other possible causes of TMJ-related symptoms include arthritis, fractures, dislocations, and structural problems present since birth.