Habitual daily masseter activity of subjects with different vertical craniofacial morphology

Little is known about the habitual daily masticatory activity of subjects with different vertical craniofacial morphology. The purpose of the present study was to compare the daily long-term muscle activity of short-face subjects with that of long-face subjects as assessed in their natural environment. Digital photographs of the facial profile were obtained from a sample of 300 subjects and the ratio between anterior total and anterior lower facial height was assessed (Vertical Facial Index: VFI). Fourteen long-face and 16 short-face subjects were selected from the opposite tails of the frequency distribution of VFI. Long-term masseter activity was monitored for 8 h d(-1) in the natural environment by means of portable one-channel electromyograph recorders over three working days. Assessments included calculation of the number of activity periods (APs) per h (N/h), their mean amplitude (A(mean)), and their mean duration (Dur). The maximal electromyogram activity did not differ significantly between the short-face and the long-face subjects. There was no significant difference between the two groups investigated in N/h, in A(mean) and Dur. The findings suggest that habitual activity of masseter muscle in the natural environment was not influenced by the vertical craniofacial morphology as assessed in the present study.