Abstract: Objective To explore the effect of intervention with unilateral mastication on masseter muscle asymmetry. Methods
Forty-three subjects (19 males and 24 females, mean age 20.0±0.5 years) with unilateral chewing were divided into group A0
with motivation and without intervention, group A1 with motivation and intervention, group B0 without motivation or
intervention, and group B1 without motivation but with intervention. In groups A0 and A1, the motivation was removed and
groups A1 and group B1 received interventions. Surface electromyography was recorded using surface electromyography in all
the subjects in mandible postural position (MPP), with maximum clenching in intercuspal position (ICP) and during chewing.
The sEMG of the left and right masseter muscle were separately recorded to assess the asymmetry index of the masseter
muscles (ASMM) and its changes after intervention. Results In groupA0, the ASMM at MPP, during maximum clenching and
chewing had no obvious changes after removal of the motivation. In group A1, the ASMM at MPP, during maximum clenching
and chewing were obviously decreased after intervention. In group B0, the ASMM at MPP and during maximum clenching
showed no obvious changes but ASMM during chewing significantly increased after removal of the motivation. In group B1,
the ASMM at MPP, during maximum clenching and chewing all decreased obviously after intervention. Conclusion
Interventions can significantly improve the bilateral symmetry of the masseter muscles in subjects with unilateral chewing,
and the motivation for unilateral chewing should be removed before intervention.