Epidemiological Investigation Of Temporomandibular Joint Disorders And Study On Surface Electromyography Of Scissors-bite

Objective: To investigate the correlation between posterior scissors-bite and TMD and analyze the EMG characteristics of the masticatory muscle on the unilateral posterior scissors-bite.Methods: 700 undergraduates were from Xinjiang Medical University and accepted examination of temporomandibular joint and occlusion.the posterior scissors-bite factors associated with the disease were identified by logistic regression analysis with SPSS20.0 software package.Three groups were divided which all from upper undergraduates included 40 people with unilateral posterior scissors-bite,40 people with unilateral joint clicking,40 people with normal occlusion no joint clicking.We recorded the surface electromyography(SEMG)of bilateral temporal anterior muscles and masseter muscles in mandibular postural position(MMP)and intercuspal position(ICP)for all groups.The rest groups were compared with normal occlusion no joint clicking and analyzed with one-way anovo variance analysis.Results: Posterior scissors-bite was a risk factor which increased the occurrence of TMD.the scissors-bite in unilateral posterior scissorsbite 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-sicssorsbite when biting ICP.Group of scissors-bite revealed a significance of a higer masticatory asymmetry index than group of nomal occlusion.A higher asymmetry index was showed in single molar scissors-bite comepared with a single premolar scissors-bite.There was no signifancance between the group of bilateral joint clicking with the group of normal occlusion about SEMG in MMP and ICP.Conclusion: Posterior scissors-bite was a risk factor which increased the occurrence of TMD,scissors-bite was related to the SEMG of masticatory muscles.