齒顎矯正疼痛對咬肌活動性之影響－齒顎矯正初期平齊化過程咬肌活動性變化與矯正疼痛之關係

Changes in masseter muscle activity during orthodontic treatment are probably due to discomfort or pain, or alterations in the occlusal relationship produced by tooth movement. This study was conducted to investigate changes in masseter muscle activity and their correlations with orthodontic pain produced by tooth movement during orthodontic treatment. Six volunteers participated in this study. Data were collected using a portable electromyogram system. Bursts of bilateral masseter muscle activity were counted over a 12-hour period 1 day before the orthodontic treatment; the same procedures were also carried out to assess muscle activity on the first to sixth, 15th, 29th days after the orthodontic wire was activated. The pain intensity was assessed using a visual analogue scale (VAS) in order to investigate the influence of orthodontic pain on masseter muscle activity. The results showed that orthodontic pain commenced and increased 4 hours after initial placement of the archwire. It peaked nocturnally on the second day, and gradually tailed off during the fifth and sixth days. Overall a diurnal variation was found with a tendency of the pain to be the worst at night on the second day, with the intensity of VAS values of 22:00＞18:00＞14:00＞10:00. However, the pain response was found to be highly and consistently subjective, and the pain threshold and persistence time both showed great individual variations. In addition, the results tested by the Spearman rank correlation showed a negative correlation between masseter muscle activity and orthodontic pain. This indicated that masseter muscle activity decreases when orthodontic pain increases, and following relief of the pain, masseter muscle activity gradually recovered. It was concluded that pain produced by orthodontic treatment reduces the masseter muscle activity.