Masseter Oxygenation Abnormalities in Individuals With Frequent Wake-time Tooth Clenching

Objectives: Wake-time tooth clenching is a risk factor for muscle pain due to temporomandibular disorders (TMD). It has been reported that the oxygenation of jaw muscles in individuals with painful TMD of muscle origin is impaired, suggesting that abnormalities in blood perfusion and/or muscle metabolism may be responsible for muscle-related TMD. Nonetheless, the oxygenation of jaw muscles in healthy subjects who are at high risk for developing myogenous TMD has been minimally investigated so far.
This study aimed at comparing the oxygenation of the masseter during standardized tasks in TMD-free individuals with frequent wake-time tooth clenching to those with infrequent episodes. It was hypothesized that individuals with frequent tooth clenching episodes have a reduced oxygenation of the jaw muscles.
Methods: The oral behavior checklist (OBC), a validated questionnaire which measures the frequency of wake-time oral behaviors, was filled out by 255 students at University of Toronto. The distribution of an OBC subscore (OBC6) computing the frequency of tooth clenching related oral behaviors was assessed. Fourteen females with high (>80^th percentile of the OBC6 distribution; HP, n=7) vs. low (<20^th percentile of the OBC6 distribution; LP, n=7) frequency of wake-time tooth clenching related oral behaviors were asked to clench at their maximum voluntary contraction (MVC) for 2 min and clench at 10-20% MVC for 20 min. Oxygen tissue saturation (StO₂), oxy- (O₂Hb), deoxy- (HHb) and total hemoglobin (tHb) of the right masseter were measured via near-infrared spectroscopy.
Results: HP individuals had lower O₂Hb, and greater HHb during both the MVC and sustained 10-20% MVC clenching tasks (all P<.001) and experienced greater muscle pain than LP ones after the experiment (P=.035).
Conclusions: Healthy individuals with frequent wake-time tooth clenching episodes have abnormal jaw muscle oxygenation which may favor the early onset of anaerobic metabolism, muscle tissue injury, and jaw muscle pain.