By Joan Wilentz, TMJA Board Member and Science Writer
The esophagus is a roughly ten-inch hollow tube that descends from your throat through the diaphragm into the stomach. Normally, it is a one-way street transporting food you swallow to the stomach for digestion. But in GERD— Gastroesophageal Reflux Disease— the flow can reverse so that stomach contents (including gastric acids) are regurgitated upwards to cause a burning sensation (heartburn), nausea, pain and other distressing symptoms. Now, American and Chinese investigators who conducted a study in two hospitals in China, have concluded that having GERD is a risk factor for temporomandibular disorders (TMD), so if you have GERD the odds are greater that you will have TMD and vice versa: if you have GERD, the odds are better than even that you will have TMD.
We paid attention to this study, published in the Canadian Medical Association Journal (http://www.cmaj.ca/content/191/33/E909.long) because it is a large one, rigorously conducted, and uses the classic case-control method to compare two groups: one with chronic TMD; the other a control group without TMD, but otherwise matched by age, sex, and other variables. The investigators’ aim was to discover if there were significant differences between the TMD group and controls who also had a diagnosis of GERD.
The Rigor: The TMD group consisted of 1,522 consecutive patients between the ages of 18 and 70 diagnosed with chronic TMD who were seen at two sites in China, one an academic (research-and- professional training-oriented) hospital, the other a non-academic hospital. The control group were 1,522 non-TMD individuals seeking dental services at the two hospitals. Dentists used the same criteria to diagnose chronic TMD in the Chinese patients as was used in the U.S.-based OPPERA (Orofacial Pain Prospective Evaluation and Risk Assessment) study that we have reported on in previous TMJ News Bites. (Criteria include at least 6 months duration of joint or masticatory muscle pain for selected numbers of hours per month). The diagnosis of GERD was made by trained gastroenterologists using a standard protocol and blinded as to whether they were examining a TMD patient or a control subject. The researchers found GERD in 132 TMD patients and 61 controls, a significant difference interpreted as an increase in the odds of having TMD if you have GERD—and vice versa: if you have TMD, you are at increased risk of having GERD.
WHY? It’s not clear why these two diseases are connected, and certainly in a case-control association study of this kind it is not possible to say that one condition like GERD causes TMD or vice versa, but the investigators also explored data from a number of psychological questionnaires and interviews with participants and came up with some overlapping issues. Patients with GERD and patients with TMD both reported disturbed sleep; both also reported higher degrees of anxiety and some measure of “somatization,” in which psychological feelings like anxiety or depression are projected into physical symptoms, affecting a body part or system. So they have added to their conclusions that anxiety, undermined sleep and somatization may “moderately mediate the relation”’ between GERD and TMD.
It seems to us that those psychological issues may be present in a number of chronic illnesses, especially ones involving pain, so we question how important they may be in mediating the connection between GERD and TMD. We wonder if changes in diet by TMD patients caused by problems with chewing and swallowing may be a factor in creating gastrointestinal problems. On the other hand, as the authors point out, the presence of GERD and frequent regurgitation of acidic stomach contents may act as an irritant sensitizing the central nervous system and pain pathways resulting in a decline in pain thresholds in the oral region. As with most scientific research, results of one study often lead to more questions to be answered. In any case, the real messages of the study are for patients and caregivers to be aware of the gastrointestinal implications for patients with TMD—and vice versa and the evidence of the complexity of TMD and the need for multidisciplinary research and treatment in TMD.