Examination of masticatory movement and rhythm before and after surgical orthodontics in skeletal Class III patients with unilateral posterior cross-bite.

PURPOSE

We examined the movement of the mandible in skeletal Class III patients with a unilateral posterior cross-bite to clarify whether the correction of the cross-bite caused conversion of the masticatory movement from a reverse to a grinding pattern.

MATERIALS AND METHODS

We studied 10 adults with mandibular prognathism who had been treated with surgery. The masticatory movement and rhythm (cycle time) during gum chewing were recorded before and after treatment.

RESULTS

The results before treatment demonstrated a high frequency of patterns IV, VI, and VII and a low frequency of patterns I, II, and III on the cross-bite side. After treatment, the masticatory movement on the cross-bite side showed different patterns than from before treatment. The high frequency of pattern VI (reverse pattern) before treatment was significantly reduced, and patterns I and III had significantly increased in frequency after treatment. No significant changes were seen in cycle time, opening phase, occlusal phase, or the closing phase before and after treatment.

CONCLUSIONS

These results suggest that correction of a unilateral posterior cross-bite induces conversion of the masticatory pattern from the reverse pattern to the grinding pattern.