Method: One hundred and ten children (9,1 ± 1.2 yr of age) with unilateral posterior crossbite were selected for the study. Electromyography and kinematics were simultaneously recorded during mastication of a soft bolus and a hard bolus.
Result: The percentage of reverse cycles in the group of patients was 57.0 ± 31.1% (soft bolus) and 68.7 ± 27.9% (hard bolus) when chewing on the crossbite side. When chewing on the non-affected side, the number of reverse cycles was 10.2 ± 21.5% (soft bolus) and 13.2 ± 21.3% (hard bolus). The reverse patterns on the crossbite side were different with respect to the patterns on the non-affected side being narrower and positioned along the vertical axis. Both types of cycles resulted in lower EMG activity of the masseter of the crossbite side than the contralateral masseter, being the activity of the non-affected side larger for reverse than for non-reverse cycles.
Conclusion: It was concluded that when chewing on the crossbite side, the masseter activity is reduced and it is similar or increased on the contralateral side, resulting in a serious asymmetrical masticatory function. The reduction in the percentage of reverse cycles is important for decreasing the altered muscular activity. The functional correction of the chewing cycles should be an important aim of the orthodontic therapy.