To study the oromaxillofacial electromyography characteristic of patients with bimaxillary protrusion and to provide reference to orthodontic treatment.

Eighteen patients with bimaxillary protrusion and eighteen persons with individual normal occlusion were included. Average electromyography data of oromaxillofacial muscles at different situations was recorded by using the Bio EMG Ⅲ surface electromyogram measuring equipment. The average electromyography data was analyzed by SPSS 20.0 software. The data of normal distribution was performed with Independent sample t Test and the one of asymmetrical distribution was performed with Wilcoxon Test.

During voluntary clenching position, the electromyography activities of anterior temporalis and masseter muscles of bimaxillary protrusion group were (55.45 ± 8.73) and (49.53 ± 6.62) μV respectively, and those of individual normal occlusion group were (80.46 ± 61.46) and (72.15 ± 6.99) μV respectively (t= 2.393, P= 0.025; t= 2.3253, P= 0.029) . During lips in contact, the electromyography activities of upper orbicularis and mentalis muscles of bimaxillary protrusion group were (21.27 ± 3.96) and (23.23 ± 3.97) μV respectively, and those of individual normal occlusion group were (7.29 ± 0.98) and (12.34 ± 2.12) μV respectively (t=-3.726, P= 0.004; t=-2.419, P= 0.019) .

There were difference of the oromaxillofacial electromyography under various functional situations between bimaxillary protrusion group and individual normal occlusion group. The electromyography activities of temporal anterior, masseter muscles weakened during voluntary clenching position. While the electromyography activities of upper orbicularis and mentalis muscles enhanced during lips in contact.