Jaw Muscle Pain Effect on Jaw Muscle Activity in Catastrophizers

Objectives: To study the effects of muscle pain on jaw muscle activity during chewing in catastrophizers. Methods: Mandibular movement was tracked and muscle electromyographic (EMG) activity was recorded from bilateral masseter, anterior temporalis, anterior digastric, and sternocleidomastoid muscles in 21 asymptomatic subjects during empty chewing for two conditions: moderate pain [continuous infusion into right masseter of 4.5% hypertonic saline to achieve a 4-6 rating for pain and unpleasantness on 0-10 numeric rating scale], and no pain [isotonic saline infusion to control for volume effects of infusion). The sequence of hypertonic and isotonic saline was randomized. Subjects completed the Pain Catastrophizing Scale and were divided into lower catastrophizers (<15/52, n=12) and higher catastrophizers (≥15/52, n=9). Average EMG root-mean-square values at 0.5 mm increments of mid-incisor-point displacement in catastrophizers were analyzed (independent t-test; P < 0.05). Results: With induced pain, pain intensity (P=0.02) and unpleasantness (P=0.005) were significantly higher in higher catastrophizers than lower catastrophizers. In comparison with no pain, there were no significant effects of induced pain on jaw muscle activity during open and close jaw movements except that the left temporalis muscle activity was significantly less in the jaw closing movement (P<0.01, paired t-test). In the higher catastrophizers group, compared with no pain, induced pain resulted in significant decrease in EMG activity in the left digastric muscle (P<0.05) during opening, and right masseter (P<0.05) and left temporalis muscles (P < 0.01) during closing. There was no significant change for lower catastrophizers. Conclusions: The data suggest that during an empty chewing task, higher catastrophizers, exhibited reduced agonist muscle activity in pain in comparison with no pain. Pain catastrophizing may influence the effect of pain on jaw muscle activity. Supported by the NHMRC of Australia, and Australian Dental Research Foundation, Inc.