When actor Burt Reynolds took to the television talk shows last year to announce that he didn't have AIDS at all, just TMJ, this obscure dental disorder took on new pop status. Clicking jaws, tension headaches and achiness in the neck and shoulders have all been ascribed to TMJ, shorthand for temporamandibular joint dysfunction. But because the symptoms are so vague -- and the victims most often women between 20 and 40 -- some think TMJ is just another trendy disease.

Is TMJ something that has long been with us but that is suddenly being seen more often because of greater awareness and more sophisticated diagnostic techniques? Or is it, as the cynics would have it, merely dentistry's way of boosting sagging practices now that the profession's biggest money maker, the cavity, has been all but conquered?

Estimates of the prevalence of TMJ symptoms in the general population range from 28 percent to 86 percent. The syndrome has been associated with jaw pain, limitation in jaw mobility, clicking or popping sounds when the jaw opens and such non-jaw symptoms as headaches, earaches, neck and shoulder pain, dizziness, sinus problems and even mental disorders.

But the presence of symptoms alone is not enough for a diagnosis of TMJ. "Clicking or popping seems to occur in about 40 percent of the population," says Dr. Daniel Laskin, head of the TMJ and Facial Pain Research Center at the Medical College of Virginia. "But that doesn't mean 40 percent of the population will need treatment." Laskin says some persons with clicking may eventually develop TMJ -- including locking of the jaw and pain in the face, neck and shoulders -- but "a high percentage will have their clicking continue all their lives and never get any worse."

According to Dr. Joseph Marbach, director of the Pain Research Unit at the Columbia University School of Public Health, TMJ only exists when an individual has pain in the TMJ or limited jaw movement or both. "A person without pain or limited jaw movement does not have TMJ syndrome -- regardless of how many other symptoms he or she may have," Marbach says.

The American Dental Association prefers the term TM disorder to remove the emphasis from the joint itself. TMJ usually is not even a joint problem at all. According to Laskin, about 75 to 85 percent of those diagnosed with TMJ really have a muscular problem, most often caused by grinding of the teeth, or bruxism.

The impression persists that TMJ is a good way for dentists to revitalize their practices, now that fluoride treatments and dental sealants have reduced the demand for fillings. Postgraduate courses are offered on TMJ management "to revitalize faltering dental practices," according to an article in the Journal of Dental Education; books tout TMJ as a way to double a dentist's patient load.

"I've actually had people come up to me and say, 'My practice is a bit slow and I'd like to earn some extra income; tell me how you get your TMJ patients," says Dr. Kenneth Clore, a dentist in Silver Spring. "What they don't realize is that this is very tedious work that requires a lot of time with patients. I can't see 20 patients in a day; on a really, really busy day, maybe I'll see eight."

Other specialists are eager to get into the act: dental specialists, such as orthodontists, periodontists (gum specialists) and pedodontists (children's dentists); medical specialists, such as oral surgeons and osteopaths; and others, such as physiotherapists, chiropractors, kinesthesiologists and massage therapists.

"TMJ spells money," wrote Dr. M.A. Pogrel of the University of California at San Francisco in a tongue-in-cheek article in the British Dental Journal, "and the one thing that must not be allowed to happen is that patients are kept waiting, so that the condition cures itself before they have had a chance to have it treated by two or three different specialists."

Pogrel recounts the succession of CT scans, MRI scans, bridges, crowns, braces and surgery that a typical patient might suffer through to seek relief from a clicking jaw. At the end of all this, after a total expenditure of more than $30,000, the patient probably isn't even cured, he writes. "However, as things stand at this moment, we have reached the end of the road, and we know of no other means of legally extracting more money."

The majority of adults have at least one sign or symptom of TMJ -- if you look hard enough. One study of Berkeley undergraduates found that 80 percent had some symptom of TMJ, and nearly 75 percent were said to have limited or abnormal jaw mobility. Clore says he screens all his patients for TMJ and finds at least one symptom in about 60 percent of them.

"Usually, it's just a crunching noise when the jaw opens, or the jaw swinging to one side when you open your mouth," he says. "The patient will say, 'Oh, yeah, I've noticed that, but it never really bothered me.' " An unscrupulous dentist might force treatment on all these patients, but Clore says only about one in three of his patients with TMJ symptoms are dysfunctional enough to really need treatment. Treatment for TMJ is as controversial as is its diagnosis. "The best treatment is the one that's most reversible," says Bob Kuska, a spokesman for the National Institute of Dental Research. This usually means pain medication, relaxation techniques and elimination of certain habits that might aggravate jaw strain, such as gum chewing, ice chewing or cradling a telephone receiver on one shoulder.

Next, a dentist might even out the level of the teeth, if jaw muscles are being strained to get around a filling that's too high or a tooth that's too long. This involves either installing crowns or grinding and filing the teeth.

And if the patient is a tooth grinder, that must be stopped. "Chronic teeth clenchers are the ones whose TMJ is likely to get worse," says Larkin. "Even if they go through surgery to correct it, it's likely to come back if they continue clenching." So the clenching itself must be stopped -- either through relaxation techniques, biofeedback, or, in the case of nighttime clenchers, the use of mouth guards that keep the teeth separated.

When Clarke Hutchinson's jaw locked shut last year, she knew it was the result of her lifelong habit of grinding her teeth in her sleep. The 35-year-old Washington woman had been waking up with jaw fatigue, listening to her jaw's clicks and pops, and suffering through episodes of jaw locking for years. "I kept thinking it would go away," she says.

By early last year, the disc in her temporamandibular joint would pop out of place every time she opened her mouth. "I had to send my jaw in one direction to release one side, and send it in the other direction to release the other side," she recalls. "It got so bad it was almost a relief when it finally just locked shut."

Hutchinson had an operation in February at the Medical College of Virginia, in which Laskin tightened up the ligaments in her jaw to keep the disc in the right position. She now wears a mouth guard every night -- it fits around her four front teeth and attaches to wires on her molars -- to keep her jaw muscles relaxed as she sleeps. "I don't think my mouth will ever be great," Hutchinson says. "But I'm certainly feeling fine now."

At one time, doctors thought TMJ was the result of a bad bite. Orthodontists still tend to treat their TMJ patients with braces -- just as physical therapists tend to prescribe exercises, psychologists tend to use stress reduction techniques and oral surgeons tend to operate. But recent studies have shown that misaligned teeth are no more common among TMJ patients than among the population at large.

Wearing braces no doubt helps some TMJ sufferers, but the improvement could be the result of a placebo effect rather than an anatomical correction. Columbia University's Marbach refers to one experiment in which TMJ patients were given a sham bite adjustment. Two thirds of them, he says, "experienced total or near total relief." In addition, Marbach adds, TMJ patients often "get better on their own simply as a matter of time."

Surgery for TMJ generally is viewed with skepticism. Oral surgeons are removing jaw disks and portions of the jawbone, cutting the ligaments of the jaw, sometimes even breaking the jaw and resetting it to correct TMJ abnormalities. New surgical techniques, such as arthroscopy, might make this procedure simpler and less risky. But for now the density of blood vessels around the TMJ means the operation involves a lot of blood loss; it also means that adhesions, or internal scars, form quickly as the surgical wound heals.

"Operating on the TMJ is not like operating on another joint like the knee or elbow," says Clore. "Adhesions mean that surgical {consequences} five years down the road may be worse than the original symptoms."

Experts advise persons who suspect TMJ to see a dentist to rule out other causes of the pain, such as arthritis, migraine headaches, phantom tooth pain, tumors or sinus infections. If the diagnosis is truly TMJ and the symptoms are enough to interfere with daily life, the first attempt at treatment, experts say, should be the least invasive.

Robin Marantz Henig, a Washington free-lance writer, is the author of "How a Woman Ages" and other books.