Every time you talk, chew, yawn, or laugh, you exercise your temporomandibular joint. This critical joint connects the upper jaw to the lower jaw. People who have temporomandibular joint disorder (TMJ) may experience stiffness, headaches, ear pain, or grinding and clicking noises in their jaw. In some cases, the jaws may even lock. About half of TMJ cases are caused by irritation of the joint itself. The other half is due to myofascial pain in the surrounding muscles.

TMJ affects more than 10 million people in the United States, most of them women in their childbearing years. Research suggests that hormones may be the culprit. A study done in 1997 by researchers at the University of Washington in Seattle found that women on hormone replacement were more than 70 percent more likely to seek treatment for TMJ than those not on hormone therapy. Similarly, women who take oral contraceptives were 20 percent more likely to have TMJ than those who did not.

TMJ typically occurs when you grind and clench your teeth at night, a condition called bruxism. The grinding and clenching is believed to the result of daytime stress.