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

Pain has been shown to have an effect on muscle activity even when it does not originate in the muscle itself or in the related joint. The effect of pain from arch wire adjustment on jaw muscle activity is unclear. This study systematically evaluated the effects of orthodontic arch wire adjustment pain on masseter electromyographic (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 TV with no gum (15 minutes). An arch wire adjustment or placebo adjustment was then made. Subjects returned after 48 hours, 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.