Symptoms and Physiological Responses to Prolonged, Repeated, Low-Level Tooth Clenching in Humans

BackgroundThe traditional view contends bruxism, such as tooth grinding/clenching, is part of the etiology of temporomandibular disorders (TMD) including some subtypes of headaches. The purpose of this study is to investigate if a low-level but long-lasting tooth-clenching task initiates TMD symptoms/signs. MethodsEighteen healthy participants (mean ageSD, 24.04.3 years) performed and repeated an experimental 2-hour tooth-clenching task at 10% maximal voluntary occlusal bite force at incisors (11.1 +/- 4.6N) for three consecutive days (Days 1-3). Pain and cardiovascular parameters were estimated during the experiment. ResultsThe task evoked pain in the masseter/temporalis muscles and temporomandibular joint after 40.0 +/- 18.0 minutes with a peak intensity of 1.6 +/- 0.4 on 0-10 numerical rating scale (NRS) after 105.0 +/- 5.0 minutes (Day 1). On Day 2 and Day 3, pain had disappeared but the tasks, again, evoked pain with similar intensities. The onset and peak levels of pain were not different between the experimental days (P=.977). However, the area under the curve of pain NRS in the masseter on Day 2 and Day 3 were smaller than that on Day 1 (P=.006). Cardiovascular parameters changed during the task but not during the days. ConclusionsProlonged, low-level tooth clenching evoked short-lived pain like TMD. This intervention study proposes that tooth clenching alone is insufficient to initiate longer lasting and self-perpetuating symptoms of TMD, which may require other risk factors.