Electromyographic activity of the sphenomandibularis and lateral pterygoid human muscles during mandibular lateral movements

Abstract

Aim. Understanding of the functional anatomy of the Sphenomandibularis muscle (SM) is limited. In order to begin to elucidate its function, the present authors determined, using electromyographic evaluations, that the (SM) displays signifcantly more electromyographic (EMG) activity (during jaw movement excursions from edge to edge to maximal intercuspation with occlusive force), than does the lateral pterygoid muscle. Methods. A descriptive, non-experimental study was conducted. Electromyographic recordings were performed with depth electrodes during movements of the mandible, both with and without occlusal contact. Five male subjects between 18 and 27 years of age underwent electromyographic study of the SM and lateral pterygoid muscles. EM activity was observed to occur only in the lateral pterygoid muscle (and not the SM), during lateral movements, with and without tooth contact, on a working side movement. Results. During both contralateral movements, without tooth contact, and also during ipsilateral movements with forced occlusal contact, we observed an increase in the SM only. During mandibular movements, from lateral to medial with forced occlusal contact, we observed strong EM activity in both muscles, with the EM activity being greater in the SM. Conclusion. The authors conclude that the SM is a lateral pterygoid agonist; coming into play during the last phase of mastication, and may play an important role in eccentric bruxism