Abstract: Objective: To investigate the correlation between unilateral posterior scissors-bite, joint clicking symptoms, and surface electromyography of masticatory muscle. Methods: The samples were from Xinjiang Medical University undergraduates and received examination of temporomandibular joint and occlusion, which included 40 people with unilateral posterior scissors-bite, 40 people with unilateral joint clicking, and 40 people with normal occlusion no joint clicking. The surface electromyography of bilateral temporal anterior muscles and masseter muscles in mandibular postural position (MMP) and intercuspal position (ICP) for all groups were recorded. The asymmetry index was counted for further comparison. Results: The scissors-bite in unilateral posterior scissors-bite side revealed a lower SEMG of the TA and MM compared with normal occlusion in MMP (P<0.05), the non-scissors-bite revealed no significance. The SEMG value of TA and MM were significantly lower than the group with normal occlusion and the non-sicssors-bite when biting ICP. Group of scissors-bite revealed a significance of a higher masticatory asymmetry index than group of normal occlusion. A higher asymmetry index was showed in single molar scissors-bite compared with a single premolar scissors-bite. There was no significance between the group of bilateral joint clicking with the group of normal occlusion about SEMG in MMP and ICP. Conclusion: Scissors-bite was related to the SEMG of masticatory muscles instead of the joint clicking.

Key words: Scissors-bite, Temporal muscle, Masseter muscle, Electromyography, Joint clicking