Neuropathic Oro-Facial Pain and Jaw Muscle activity during Free-Chewing

Objective: To determine the effect of neuropathic orofacial pain (NOP) on jaw muscle electromyographic activity during gum chewing. Introduction: Chronic NOP affects up to 11% of the population. We hypothesised that a history of NOP will cause enduring brain changes resulting in sensorimotor function alterations. Specifically, jaw muscle EMG activity changes will outlast the duration of the pain complaint. Methods: Thirteen subjects with NOP (mean age 63.6±9.5 yrs) and 15 healthy pain-free control subjects (62.2±6.9 yrs) were recruited. The subjects in the NOP group had a history of pain for 3-36 yrs but were not in pain during the experimental recording session. In each subject, muscle activity was assessed with surface electrodes placed bilaterally over the anterior temporalis, anterior masseter and the right anterior digastric muscles. Jaw movements (JAWS3D) were recorded during two 15 s trials of free chewing of gum on the right side. The root mean square muscle activity was calculated at each 0.5 mm of jaw displacement in the opening and each closing phases of the chewing movement. The activity of each recorded jaw muscle was compared between control and NOP groups with linear mixed effects statistical analysis. Results: Comparison demonstrated a significant (p<0.05) group*displacement interaction for the right masseter muscle (NOP group) during the closing phase and the right temporalis (NOP group) for the opening phase of chewing. There were no other significant interactions. Conclusion: Results suggest that there is a long-term effect of NOP on jaw muscle activity. These effects may reflect the significant changes, in comparison with controls, in brain anatomy and biochemistry in the brains of NOP patients (Gustin et al. J. Neurosci. 31; 5956-5964, 2011). Acknowledgement: Support: Australian NHMRC Australia, Australian Dental Research Foundation, ADA (NSW Branch), Hamdard University, Pakistan.