Jaw pain is the most common kind of musculoskeletal pain after low back pain, affecting about 20 million Americans. Fittingly, it has a jaw-breaking name: temporomandibular disorder (TMD).

The jaw hinge connects the lower jaw (mandible) to the temporal bone on each side of the head. Sometimes this joint hurts, clicks and/or locks painfully. Jaw muscles may become sore, making it hard to chew. Pain may radiate to the facial and neck muscles, the head, ears and teeth; it may persist around the clock.

Causes and controversies of TMD

There are many theories about the causes of TMD. Some of the obvious ones are injury to the jaw or arthritis in the joint. Genetic factors may play a role. Some dentists blame grinding or clenching the teeth (bruxism), especially at night, or dislocation of the disk that cushions the jaw joint. Emotional stress is often cited as a cause of both teeth grinding and TMD. Gum chewing, nail biting and eating chewy foods or crunchy candies might also contribute, as may bad posture, particularly thrusting the chin forward, which can strain the neck and jaw muscles. TMD is hard to diagnose and treat, probably because it may be a lot of different problems that vary from person to person.

First step: self-care

• Try over-the-counter pain relievers; apply hot or cold compresses to the jaw. Massage your jaw muscles and temples.

• Eat soft foods; take small bites. Give up hard and chewy foods, like bagels and dried fruit, for a while. Don’t chew gum.

• Do gentle jaw stretches. Slowly open and close your mouth. Let your jaw hang slightly when you are not chewing, swallowing or speaking.

Next step: professional care

• If the pain persists, consult your dentist. In the past, correcting malocclusion (teeth that don’t fit together properly) by grinding down a few tooth surfaces was regarded as a good treatment, but more recent research suggests it may not help TMD much. Though its benefits for TMD are also questioned, mouth splints (worn while sleeping) may help stabilize the bite and eliminate nocturnal tooth grinding. If you try a splint, a low-cost athletic mouth guard may work as well as a custom device.

• If stress is contributing to your TMD, professional counseling may help. TMD may respond well to relaxation training, biofeedback and distraction therapy. Small but well-designed studies have found that acupuncture can be useful, too, at least in the short term.

• TMD may improve with time and go away on its own. If it does not, a referral to an orofacial pain management clinic or TMD center affiliated with a hospital or university may be the next best step.