The effect of tongue position and resulting vertical dimension on masticatory muscle activity. A cross-sectional study

The purpose of this study was to: (a) compare the tonic electromyographic (EMG) activity of the temporalis and masseter muscles between two tongue positions, (b) compare the vertical dimension (VD) resulting from each tongue position and (c) determine the influence of the VD on the tonic EMG activity for each tongue position. Thirty-three healthy dental students with natural dentition and bilateral molar support, between the ages of 18 and 22years, with no prior history of oro-facial injury, or current or past pain in the jaw, mouth, or tongue participated in the study. Tonic masseteric and temporalis EMG activities were recorded using surface electrodes. Subjects were instructed to passively place the tongue either on the anterior hard palate or in the floor of the mouth. At each tongue position, the resulting EMG and VD were recorded. No significant difference in EMG activity was found for either the masseter (P-value=05376) or temporalis muscle (P-value=07410), between the two tongue positions. However, there was a significant difference in the VD resulting from the two different tongue positions, being greater with the tongue placed in the floor of the mouth. There was no statistically significant correlation between VD and EMG activity for both tongue positions. In spite of the lack of difference in the effect of both tongue positions on the masseteric and temporalis EMG activity, an increment of the VD was registered for the floor of mouth-tongue position. However, VD was not correlated with EMG activity for both tongue positions.