In this study mean amplitude values obtained from mentalis, Masseter and OOS muscles electromyografic records of adults with normal occlusion and with Class III malocclusion were compared. As regards to Class III malocclusion, it was determined that mean amplitude values decrease and enough interference could not be formed due to the hypofunction of mentalis muscle related to mandibular protrusion and increase in low face height. There was no significant differences between normal and Class III malocclusion cases for the masseter muscle. Decrease of mean amplitude values were observed for the OOS muscle it was not showing maximal contraction due to the its hypofunction.

Keywords: Class III Malocclusion, Mentalis, Masseter and OOS, EMG