You need it for talking, chewing, smiling, yawning, laughing and singing.  It’s the jaw joint—technically known as the temporomandibular joint (TMJ)—one of the hardest working and most complex joints in your body.  You usually don’t give it a second thought, and you usually don’t need to.  But if something goes wrong, your TMJ can cause nagging pain and limit the flexibility of your jaw.  In extreme cases, the pain can be long-lasting and debilitating. 

More than 10 million Americans have TMJ disorders, according to some estimates.  They’re usually first noticed as a pain in the chewing muscles or jaw joint.  Other symptoms may include stiffness or locking of the jaw; painful clicking, popping or grating in the jaw joint; or a change in the way the upper and lower teeth fit together.  The symptoms usually go away by themselves.  But occasionally, the pain and limited jaw movement may persist for a long time. 

Jaw injuries sometimes cause TMJ disorders.  But usually the underlying trigger is unknown.  Many people believe that stress and tooth grinding are major causes of the condition.  However, the research is still unclear.  Some studies even suggest that TMJ disorders themselves lead to stress, rather than the other way around.  Research also disputes the common belief that a bad bite or orthodontic braces can lead to TMJ disorders.  And there’s no scientific proof that clicking sounds in the jaw joint cause serious TMJ problems. 

With so much uncertainty about the causes, there’s also little certainty about treatment.  The most widely used therapy is a plastic guard—sometimes called a stabilization splint or bite guard—that fits over the upper or lower teeth.  But studies of its ability to relieve TMJ pain have been inconclusive.

To get some definitive answers about the cause of TMJ disorders, NIH is now funding the largest study of its kind.  Researchers are following more than 3,000 healthy adults for 3-5 years to see who will develop the disorders.  This study will hopefully allow scientists to tease out the factors that can cause the TMJ to malfunction.  Their preliminary findings suggest that genes can play a role.  They found that people with certain genes are less sensitive to pain and much less likely to develop TMJ disorders.

As researchers learn more about what causes TMJ problems, they’ll also find better ways to diagnose, treat and prevent the condition.  But until that happens, experts recommend taking simple steps to relieve pain and avoiding procedures, like surgery, that can permanently change your bite or jaw.