Experimental Chewing in Myofascial Pain Patients

Aims: To evaluate the potential capacity of a chewing exercise to differentiate chronic myofascial pain (MFP) patients from healthy controls and to test whether there are distinct pain response differences among MFP patients. Methods: Eighty-nine subjects participated in the study; 49 were diagnosed as belonging to the MFP subgroup of temporomandibular disorders (TMD) and had suffered from MFP for at least 6 months, and 40 healthy age- and gender-matched subjects comprised the control group. After completion of a clinical examination, all subjects performed a chewing exercise. Subjects chewed on half a leaf of green casting wax for 9 minutes and then held their jaw at rest for another 9 minutes. They indicated the intensity of the pain experience on a visual analog scale (VAS) every 3 minutes from the beginning (P0) to the end (P18) of the chewing exercise. Only changes in pain report of more than 5 mm on the VAS were considered. Analysis of covariance with repeated measures was used to analyze fluctuations in pain levels during the test, with the pain level at baseline (P0) as a covariant. Results: Statistical analysis revealed a significant main effect for group (MFP versus control); a significant main effect for activity (chewing versus rest); an interaction between activity and time; and an interaction between activity, time, and group. The latter revealed the significant effect of the chewing activity on pain levels in both groups along the axis of time and its recovery at rest. In the MFP patients, pain had increased by 32 mm at P9 in 84% of the patients and recovered to almost the initial pain levels by P18; 6% reported a decrease in pain sensation and 10% reported no change in pain. In the controls, pain had increased 4.9 mm by P9, a value within the recording error range of the scale. Conclusion: (1) A strenuous chewing exercise is a potentially beneficial tool in the diagnostic process of myofascial pain patients and, if validated, could be incorporated into clinical examinations. (2) The increase in pain intensity following the chewing exercise is typical of most of the MFP group. (3) The phenomenon of pain decrease in a small percentage of MFP patients should be further investigated. Keywords: chewing test, myofascial pain, temporomandibular disorders