TMJ and Tooth-Grinding: A Surprising Finding

Over the decade researchers studying Temporomandibular Disorders (TMD) have concluded that these conditions are complex in origin. Some combination of genetic, sex, environmental and behavioral factors gives rise to symptoms of jaw pain and dysfunction. But that conclusion contradicts the long held beliefs by many patients and dentists who think that jaw problems are caused by tooth-grinding (bruxism) during sleep. The presumption behind this is that the activity of jaw muscles would stress the muscles and wear on the jaw joint? Wrong!

A definitive study conducted by researchers at New York University (NYU) College of Dentistry, Weill Cornell Medical College, New York and the University of Montreal led by NYU investigator Karen Raphael refutes the idea that bruxism causes TMD.

To begin with, the team noted that the bruxism theory was largely based on patients’ believing that they bruxed in their sleep (often reinforced by dentists telling them so).  For that reason the researchers designed a study using polysomnographic recordings (PSG) of patients and controls in the setting of a sleep laboratory. PSG recordings include audio and video data along with measures of jaw muscle activity to determine how many episodes of sleep bruxism (SB) occur during the night, distinguishing them from other muscle activity such as yawning, talking or chewing. Over two consecutive nights they compared TMD patients with matched controls. Wanting to get the best data, the researchers scheduled the first night of the study to enable the participants to get familiar with the lab setting and instrumentation, thus allowing the experimenters to concentrate on the second night for data analysis. The team recruited 124 women patients diagnosed with myofascial (muscle-based) TMD from NYU’s dental school clinics and compared them with a control group of 46 women who were either acquaintances of the patients or recruited from other NYU clinics and well-matched in age and other demographics. Neither group was initially recruited based on whether they believed that they bruxed or not.

Here’s what the investigators found:

• In follow-up interviews 55.3% of the TMD group said they were told that they were sleep bruxers (SB) compared to 15.2% of controls.
• But actual PSG measurements showed much lower and very similar rates of SB in both groups: patients 9.7%; controls 10.9%.
• Grinding noises (but not meeting SB criteria) were common in both groups: 78.3% for patients; 59.7% for controls.
• Overall, both groups spent an average of less than one minute per night in SB episodes and less than 5 minutes in total activity involving the chewing muscles.
• Within the patient group those found to be bruxers
  reported less pain and less interferences with daily activities
  than the non-bruxing patients. 

The authors conclude: “Our study should lay to rest any remaining beliefs regarding a relationship between SB and the course of myofascial TMD. Although there may be other reasons for treating SB (for example, tooth wear) the treatment decision should not be based on a concern for maintaining or exacerbating a chronic, painful myofascial TMD condition.”

We asked Dr. Raphael to comment on her study. Her response: “When your dentist tells you that your facial pain is somehow ‘your fault’ because you are grinding your teeth, you now know that it is simply not true. Many people grind their teeth a little bit at night, but that activity cannot account for your pain. If anything, people who suffer from the most severe TMD pain are actually the least likely to grind their teeth at night. If you are thinking about getting treatment for sleep grinding to help reduce your pain, think again: It is likely to be a waste of time, energy and money.”