A new way for TMJ

In the 1970s and '80s, many people were told that their jaw ached because of a problem with their temporomandibular joint (TMJ), the hinge-like connection on either side of the head that allows the lower jawbone to move up and down. Physicians and dentists believed that the joint needed to be fixed to get rid of the pain — and, furthermore, that a bad bite (the medical term is malocclusion) was often the reason the joint didn't work properly, in much the same way that an ill-fitting shoe might throw an ankle, knee, or hip out of whack. As a result, jaws were operated on and all sorts of dental work — braces, crowns, the grinding down of teeth — was done to fix bad bites.

But since the late 1990s, the thinking about TMJ disorders has changed. Clinicians aren't nearly so quick to point a finger at a malocclusion or a faulty temporomandibular joint. There's more attention paid to sorting out the myriad sources of jaw and facial pain, which can range from a dental problem to migraine headaches to clenching the teeth because of anxiety and stress.

Dr. Jeffrey Shaefer, a TMJ disorder expert at the Harvard School of Dental Medicine, says it's often best to tackle several problems at once because the pain may have several interrelated sources. And, for the most part, the kind of dental work done in the past is now low on the list of interventions.

Insurance coverage remains iffy, so people who are about to get treated for a TMJ disorder should look into exactly what their policies cover. It's not unusual for dental insurers to classify some treatments as medical and therefore not their responsibility, and, similarly, for medical insurers to classify some treatments as dental. Moreover, some insurers may also restrict coverage to care provided by certain dentists or doctors.

Clever engineering

The temporo- in temporomandibular refers to the temporal bones that form the sides of the skull, and –mandibular refers to the mandible, the medical term for the lower jawbone. Each temporal bone has a notch in it just in front of the ear. The two ends of the horseshoe-shaped mandible fit into those notches (see illustration) to form the TMJ joints. The ends of the mandible, or condyles, are wrapped in layers of tough but pliable fibrous cartilage that withstand shearing. Ligaments hold everything in place.

Despite the unwieldy name, the temporomandibular joint is another example of just how cleverly our bodies are put together. When you open your mouth a little, the condyles of the mandible rotate. In that limited range of motion, the joint works like a fixed hinge. But open wider, and the condyles rotate forward in the notches. This second, rolling kind of motion is called translation, and it allows the lower jaw to swing open without interfering with breathing or swallowing. You can get a firsthand feel for these movements by placing your fingertips on the sides of your head near the openings of your ears while opening and closing your mouth several times.

It takes a surprisingly large number of muscle groups, relaxing and contracting in a coordinated fashion, to operate this elegant joint. It's pretty obvious from even a cursory look at the anatomy that the masseter muscles are instrumental: they form a thick band that connects the mandible to the cheekbone on both sides of the face (masseter comes from the Greek word maseter, for chewer). It's not so obvious, though, that many other muscle groups are involved, including some on the sides of the head (the temporalis muscles), in other parts of the face (the pterygoid muscles), and several in the neck. Part of the reason that TMJ problems are sometimes difficult to pin down is because the joint has connections to several muscle groups.

Noisy is not a problem

The classic TMJ symptom is a dull ache on one side of the face that gets worse with chewing. The pain may radiate, spreading to the area around the ear, the side of the head, and the back of the neck. Some people also get headaches. The jaw sometimes clicks or produces a cracking, grinding sound (crepitus) because the cartilage in the joint is out of place. It may sound bad, but unless it's painful, a noisy jaw by itself usually isn't cause for concern or treatment.

Some TMJ problems do originate in the joint itself. Conditions like rheumatoid arthritis and osteoarthritis that affect other joints also affect the TMJ. Some people have an overall problem with loose joints, including the TMJ. Worn or misshapen cartilage doesn't always cause pain, but it can.

Often, though, the main problem is muscle pain, which occasionally can be traced back to a faulty TMJ but more commonly comes from other sources. For example, many people with a TMJ disorder grind their teeth at night. One study found evidence of grinding (bruxism) in 78% of TMJ patients. Besides being bad for the teeth, all that extra motion can overwork the masseters and the other jaw-related muscles.

TMJ symptoms frequently occur when people are under stress because they're clenching their teeth all the time without being aware of it, and clenching also puts a strain on jaw and facial muscles. Taut head and face muscles can lead to headaches.