For millions of people with mysterious pain of the jaw region, there may be help on the way.
Researchers at the University of Maryland Dental School hope their new seven-year, $17 million study of 3,400 study subjects will finally identify the cause and effect, and point to possible cures for temporomandibular joint and muscle disorders (TMJD).
For most people, the discomfort from the commonly called "TMJ" group of disorders will eventually go away with little or no treatment says the National Institute of Dental and Craniofacial Research (NIDCR) in Bethesda. However, many TMJD patients develop significant, long-term problems that cause chronic pain and dysfunction in the jaw joint and muscles that control jaw movement.
As much as 2 percent of the U.S. population suffers from TMJD, with more women than men appearing to have the condition, but doctors and scientists know little about the causes, and so there are few effective treatments.
Joel Greenspan, PhD, a professor and chair of the Department of Neural and Pain Sciences at the Dental School, says that most people know someone with the disorder or have heard their doctor suggest that a pain may be TMJD. "But, there is often little or nothing physically wrong that can be identified. And, frequently the pain is not specifically focused or limited to the jaw," he says.
Common characteristics of TMJD include pain, limitations in mobility and function, and jaw joint noises - clicks, pops, catches, or locks when the mouth is opened. TMJD is the second leading cause of pain for people who report facial or head pain.
Greenspan is one of the principle investigators in the $17 million "Orofacial Pain: Prospective Evaluation and Risk Assessment" (OPPERA) study, funded by the, NIDCR, which is part of the National Institutes of Health. OPPERA is being conducted at four sites, the University of Maryland Dental School, and the universities of Buffalo, North Carolina, and Florida dental schools. It is headed by William Maixner, DDS, PhD, Center for Neurosensory Disorders, School of Dentistry, University of North Carolina.
In some cases, the disorder can be brought on by trauma. Greenspan said some dental procedures can bring it on, but that is uncommon. It can also be brought on by misalignment of teeth, which is most often hereditary. Overuse of the jaw is another possible cause. Excessive gum chewing, nail biting, and gnawing on items like plastic straws can overtax the muscles of this joint.
"The main purpose of our OPPERA study is to identify the precursors in a prospective way, thus allowing us to more formally determine cause and effect, rather than just associations", said Greenspan. He said there have been very few studies that address the cause of the disorder in a prospective manner, and none of the size and comprehension of OPPERA. Almost all of the clinical literature studies on TMJD are either observations on TMJD patients, or case-control studies.
Historically, doctors routinely recommended surgery to try to correct TMJD, but surgery is no longer a leading recommendation. Dental treatments include filing teeth down to make them fit better in the bite, or using dental appliances to even out the bite, like a match box under a table leg. "But, sometimes grinding makes things worse and may not be the answer. Noninvasive techniques are better recommended, such as appliances or reduced stress through exercise," said Greenspan.
TMJD occurs at least two times more frequently in women than in men, and often with more severe symptoms in women, perhaps because women are more pain sensitive, he said. "Several studies conducted here and elsewhere have shown that under controlled test conditions, women report standard test stimuli as more painful than men. Recent testing we have completed indicates that the brain's processing of pain is amplified more in women than men, and even more so in women suffering with TMJD."
In an NIDCR survey of 42,370 adults, (ages 18 to 75 and older) over a six-month period prior to Dec. 20, 2008, 3.5 percent of males and 6.9 percent of females reported pain in the jaw joint or in front of the ear more than once. The average for participants ages 75 and older of both sexes combined was 3.9 percent, but the average for those in the 18 to 34 year old group was 6.5 percent.
One mystery of the disorder is that the pain is not necessarily directly focused on the jaw, while another is that the pain is not related to the extent of tissue injury. This doesn't surprise Greenspan because, he says, pain is the result of multiple system changes. "This is a complex area," he says, involving the three factors underlying pain: genetics, psychology, and physiology.