Electromyographic analysis of mentalis muscle during lip function

Objectives: The purpose of this investigation was to study the characteristic of the surface electromyographical activity of the mentalis muscle during functional activity of the lower lip. Materials and Methods: The nine subjects, aged 24-31 years, had complete natural dentitions, and no problems with chewing or swallowing. A digital electromyogram (EMG) recording device (Muscle Tester ME3000P) and bipolar silver/silver-chloride electrodes were used to record the surface EMG from the mentalis muscle (Ment), the masseter muscle (Mm) and the anterior belly of the digastric muscle (Dig). Muscle activity was recording during maximal voluntary contraction (MVC) in the intercuspal position, maximal opening of the mouth (MaxO) and three tasks (sucking on an empty straw, smiling and swallowing water from a cup). Ment and Dig activity was expressed as a percentage of MaxO, and masseter muscle activity was expressed as a percentage of MVC. The difference between the tasks on the individual muscles was analyzed by the Kruskal-Wallis rank test. A Multiplex comparison was used when a significant difference was accepted in a result of the Kruskal-Wallis rank test. Results: In sucking on an empty straw, the Ment and Dig showed strong EMG activity. In smiling, the EMG activity of the Ment was stronger than MaxO. In swallowing water from a cup, the EMG activity of the Ment, Dig and Mm was the smallest of the tasks. In the EMG activity of Ment and Dig, there was no significant difference between the tasks. On the other hand, the EMG activity of the Mm during smiling was significantly stronger than the other tasks (P=0.003). Conclusion: The results indicated that the EMG activity of the Ment during sucking on an empty straw and smiling were stronger than the EMG activity of maximal opening of the mouth.