The effect of pain from orthodontic adjustment on masseter muscle electromyographic activity arch wire

(EMG) activity and on the swallowing threshold. The EMG recordings were made on 22 subjects (ages 11 to 15) under three conditions: chewing five peanuts (10 seconds), watching TV chewing gum (15 minutes), and watching -rv with no gum (15 minutes). An arch wire adjustment or placebo adjustment was then made. Subjects returned after 48 h0urs, and the EMG measurements were made under the same conditions. After 3 weeks, subjects received arch wire or placebo treatment in a crossover design with identical recording procedures. The EMG levels while chewing peanuts decreased in 18 of 22 subjects after treatment, compared with 9 of 22 subjects after the placebo. While watching TV with gum, the EMG levels of 20 of 22 subjects decreased after treatment, compared with 9 of 22 subjects after the placebo. The number of chewing strokes before swallowing increased significantly after treatment compared with after placebo. The results suggest that orthodontic pain on teeth tend to reduce muscle activity during function. (AM J ORTHOD DENTOFAC ORTHOP 1994;106:365-70.) A common clinical observation is that after the application or adjustment of orthodontic arch wires, a patient will avoid chewing hard foods for a few days? This avoidance could be the result of conditioned, and/or nociceptive reflexes in re: sponse to the pain associated with the initial tooth movement after orthodontic arch wire activation. Ngan et aI? found a significant increase in the levels of discomfort after insertion of either separators or arch wires at 4- and24-hour intervals but n6t at 7 days. Pain receptors exist in the periodontal ligament: Pain is believed to be a result Of the effects of compression or tension of these endings? It has been shown that pain has an effect on muscle activity even When it does not originate in the muscle itself Or in the related joint. High et al. 3 measured maximum biting force and subjective pain levels before and after the extraction of third