Scientists with the University of Maryland Dental School and collaborators at three other major universities reported results from the first three years of the world's largest study yet of a mysterious yet common pain syndrome involving the jaw on May 7 at the annual scientific meeting of the American Pain Society (APS). This year it is being held at the Baltimore Convention Center.
The seven-year, $19 million study of more than 3,400 people is aimed at finally defining the causes and effects of temporomandibular joint disorder (TMJD) and ultimately leading to cures and new treatments, said Joel Greenspan, PhD, MS, professor and chair of the Department of Neural and Pain Sciences at the Dental School.
Doctors often find that people complaining of the disorder show no signs of anything physically wrong and some aspects of the disorder have stymied scientists for decades. However, Greenspan said, "I think we are going to be able to say a lot of things definitively [at the APS meeting]."
For most people the discomfort from the commonly called "TMJ" related disorders will eventually go away with little or no treatment, according to the National Institute of Dental and Craniofacial Research (NIDCR) in Bethesda. But such resolution often takes years, and for many TMJD patients the situation is much worse, said Greenspan.
At the APS meeting, Greenspan and other study leaders reported significance new evidence that people with TMJD have significantly more generalized pain sensitivity. "We see that correlation on a whole variety of measures in the clinic, such as heat and mechanical pain sensitivity, for example," Greenspan said. It is also very clear that people with TMJD have a greater likelihood of suffering from other chronic pain conditions than people without TMJD. ý
Some evidence has surfaced that psycho/social factors contribute to persistence of TMJD, as well as negativity, said Roger Fillingim, PhD, professor, Department of Community Dentistry and Behavioral Science Professor, University of Florida, who explained "lots" of data support the association of psycho/social roles.
The study leaders also expressed some surprise that prevalence of pain associated exclusively with the jaw joint was very rare, that pain is commonly associated also with the jaw muscles.
Second, the size of the study data is significant, said Greenspan. "The fact that we are getting so much information on the patients' demographics, behavior habits, physiology, psychological measures, and genetic variation, gives us the opportunity to look at how all these factors relate to the condition of TMJD."
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.
Researchers at the Dental School, and the dental schools at the universities of Buffalo, North Carolina, and Florida, are collecting data on all the possible causes, e.g., grinding teeth, stress, trauma, psychological factors, and others, ranking the factors and analyzing multiple combinations of the factors.
"Although there have been many smaller studies of individual or a few factors, this is unique because we are looking at all of these variables," said Greenspan. "The volume of data we have is almost mind-boggling."
At the APS meeting, Greenspan and other team leaders will be discussing the features that characterize TMJD patients, which will ultimately lead to identifying the predictive biomarkers of TMJD. ýHe said the approach is being considered by scientists as a tool to use to study other very complicated medical conditions. "Some [researchers] have asked for our manual of operation," said Greenspan.
The study is called Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) and is funded by the NIDCR, part of the National Institutes of Health. It is headed by William Maixner, DDS, PhD, of the Center for Neurosensory Disorders, School of Dentistry, University of North Carolina.
Maixner answered a question about the huge size of the study, "It is prototypical of a pain population because it cuts across so many groups (of people). ýSo, it is a convenient cohort to study certain hypotheses."
Historically, dentists routinely recommended surgery to try to correct TMJD, but surgery is no longer a leading recommendation. Dental treatments include filing down teeth to make them fit better in the bite, or using dental appliances to even out the bite, like a matchbox 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. However, these treatments are not as successful as one would like.
TMJD occurs at least twice as often in women than in men, and often with more severe symptoms in women, perhaps because women are more pain sensitive, he said. 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.