Changes in the masticatory jaw movement following orthodontic traction of an impacted and transposed upper canine and occlusal adjustment

In a 10-year-old female with an impacted and completely transposed upper left canine, posterior temporal muscle activity and jaw movement during mastication were examined before and after orthodontic traction of the canine, alignment of teeth, and occlusal adjustment of the canine. After the orthodontic treatment, but before the occlusal adjustment, esthetic improvement in the static occlusion was achieved. The posterior temporal muscle on the non-chewing side exhibited earlier bursts in the electromyography. Jaw movement trajectory of the jaw-closing phase at a level close to the maximum intercuspation position was more to the medial side on the frontal view, and the jaw-closing velocity in the lateral direction was slower during left-sided chewing. Following occlusal adjustment of the transposed canine, however, the muscle activity and jaw movement patterns were improved to normal patterns. We suggest that it might be advisable to perform occlusal adjustment at an early stage during the retention period in such cases.