Definition of TMJ disorders:

Temporomandibular joint disorders (TMJ disorders) are problems or symptoms of the 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 and emotional 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 example, daily stress can lead you to clench and grind your teeth, both during the day and at night while you sleep. Clenching means you tightly clamp your top and bottom teeth together, especially the back teeth. The stressful force of clenching causes pressure on the muscles, tissues, and other structures around your jaw.

Many people who clench also grind their teeth. Grinding is when you slide your teeth over each other, generally in a sideways, back-and-forth movement. This action may wear down your teeth and can be noisy enough at night to bother sleeping partners.

Poor posture can also be an important factor in TMJ. 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.

All of these stresses can result in "trigger points" -- contracted muscles and pinched nerves 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.