Influence Of Unilateral Mandibular First Molar Loss On The Activities Of Masticatory Muscles

Objective To investigate the electromyographic characteristics in the anterior temporal and masseter muscles of patients with long-term unilateral mandibular first molar loss. This study aimed to find the changes of elctromyography and the function of masticatory system in patients with long-term loss of unilateral mandibular first molar.Methods Eighteen patients between 20 and 26 years of age with one-year or more than one-year loss of unilateral mandibular first molar were selected as experimental group, and eighteen volunteers from similar places,have similar dietary habits in the same age and gender with normal occlusion were participated as control group. Surface electromyography was used to record the electrical activities of bilateral anterior temporal and masseter muscles in mandibular postural position(MPP),maximal clenching in intercuspal position(ICP) and masticating situations. Calculate the asymmetry index of anterior temporal muscles and masseter muscles in MPP and maximal clenching situations and measure the value of masticating cycle,active phase and intermittent phase. The data were analyzed using SPSS 17.0 software package to compare the differences among groups.Results(1)The average electrical activities of anterior temporal and masseter muscles in MPP of experimental group were significantly higher than the contral group,and the missing side was higher than the non-missing side(P<0.05).(2)The average electrical activities of anterior temporal and masseter muscles in maximal clenching and masticating were significantly lower than the control group,especially in the masticating situation(P<0.05).(3)The asymmetry index of anterior temporal muscles and masseter muscles in MPP and maximal clenching were significantly different(P<0.05).(4)In masticating situation,the value of masticating cycle in both missing side and non-missing side were longer than the control group,and the missing side was longer than the non-missing side(P<0.05).(5)In masticating situation,the value of active phase and intermittent phase in both missing side and non-missing side of the experimental group were longer than the control group(P<0.05),the ratio of active phase and intermittent phase in the missing side of the experimental group was higher than the non-missing side and the control group(P<0.05).Conclusion Long-term loss of unilateral mandibular first molar can affect the electrical activities of bilateral anterior temporal muscles and masseter muscles and the function of masticatory system in the experimental group.These results also suggest that it might be one of the potential factors on masticatory system disorders.