Insights into potential causes of temporomandibular joint disorders

New findings about painful jaw problems that plague millions of Americans are leading to a better understanding of pain disorders.

The results, from the first large-scale clinical study of its kind, provide insights into potential causes of temporomandibular joint disorders, known as TMD.

The findings, published in the November issue of the Journal of Pain, should lead to new methods of diagnosing facial pain conditions, predicting who will be susceptible to them and new treatment approaches.

The new results are from the Orofacial Pain Prospective Evaluation and Risk Assessment study, or OPPERA. Researchers followed 3,200 initially pain-free individuals aged 18 to 44 for three to five years.

Temporomandibular joint disorders produce pain that radiates from the jaw and surrounding muscles, restricting jaw movement and causing considerable suffering. Although the disorders vary in duration and severity, for some people the pain becomes a permanent feature of their lives.

"Previous studies haven't been able to be as conclusive as OPPERA because they've often included fewer participants and didn't follow participants for an extended amount of time," said the study's program director Dr. William Maixner, who is also director of the Center for Neurosensory Disorders at the University of North Carolina at Chapel Hill School of Dentistry. "OPPERA is allowing us to study potential biological, psychological and genetic risk factors over a longer period of time, so we will be able to better evaluate the association of these factors with TMD. This novel study will also allow us to learn more about pain disorders in general, and will improve our ability to diagnose and treat chronic pain conditions across the board."

In the results reported in the journal, the investigative team compared the initially pain-free individuals with 185 people who had long-standing, chronic TMD. They identified a number of demographic, biological, psychological and genetic factors associated with chronic cases of the condition, including:

• Chronic TMD became more frequent with increasing age in women, but not in men. This refutes previous views that the risk was greatest during a woman's early childbearing years and decreased thereafter.
• A wide range of biological and psychological factors appear to contribute to the condition. Compared to pain-free individuals, people with TMD were much more sensitive to mildly painful sensations, they were more aware of body sensations, and they experienced greater heart rate increases during mild physical and psychological stress. The findings provide evidence that chronic TMD is at least partially linked to a person's perception of and ability to suppress pain, which is determined by the body's physiological regulatory systems.
• Researchers also identified new and important genetic factors that appear to be linked to chronic TMD. Several genes, including some known to influence stress response, psychological well-being and inflammation, were identified and may result in new targets for drugs to treat temporomandibular joint disorders and related chronic pain conditions.

The longitudinal study builds on earlier work by members of the multi-university research team, who designed a broad conceptual model to determine the condition's causes. Maixner said the new findings go far towards validating that model, which was first published in 2006.

"The model, like a compass to a traveler, predicts the route ahead in the development of specific persistent pain disorders," Maixner said. "In this case, we predicted that biological and psychological risk determinants, which are modified by both life history and genetic factors, contribute to the onset and persistence of TMD."

The research team will publish additional findings and insights as they continue to analyze the study data.