The relationship between the craniofacial morphology and the fatigability of the masseter muscle during isometric contraction

The purpose of this study was to evaluate the relationship between craniofacial morphology and the fatigability of the masseter muscle during isometric contraction.Data were obtained from 23 healthy Japanese males (25.7 ± 3.8 years). EMG signals were taken from bilateral masseter muscles. The subjects were instructed to perform maximal clenching for 10 s. The analyses were conducted using 2–4 s sampling (T1) and 8–10 s sampling (T2) of 10 s sampling. The integrated EMG (IEMG) and the median frequency of the power spectrum for EMG (MF) were determined for each sampling. The fatigability index (FI) was determined by calculating the ratio of (T1–T2) to T1 for the MF. Lateral cephalograms were taken to evaluate the craniofacial morphology. Thirteen angular and 10 ratio variables were constructed for the craniofacial measurements. Paired t-tests were used to determine the mean differences for each EMG measurement between T1 and T2. Pearson's correlation coefficients were calculated to determine the correlation between the cephalometric parameters and the FI values.Both the IEMG and the MF for EMG significantly decreased from T1 to T2. The FI values were positively correlated with Y-axis, palatal plane angle, occlusal plane angle, anterior facial height and molar height and also negatively correlated with anterior lower facial height and maxillary anterior tooth height. These results suggested that the fatigability in the masseter muscle might therefore be associated with the craniofacial morphology.