Multidirectional lip-closing force in adults with mandibular deviation

The purpose of this study was to investigate the relationship between multidi-rectional lip-closing force and facial soft tissue morphology in adults with mandibular deviation. Fifteen Japanese adults with mandibular deviation participated in this study. The deviation value was defined as the horizontal distance between soft tissue menton and the facial midline. The side of the soft tissue menton relative to the facial midline was defined as the deviated side and the opposite side as the non-deviated side. The signals of directional lip-closing force (DLCF) were investigated in 8 directions. Total lip-closing force (TLCF) was calculated by adding DLCFs in 8 directions. Correlations and differences between the variables were analysed statistically. Significant positive correlations between TLCF and DLCFs were determined in six directions with the exception of the horizontal direction. Significant positive correlations for seven pairs of opposing DLCFs were found. The lower non-deviated DLCF was smaller than the three pairs of opposing lip-closing forces. Negative significant correlation was found between the deviation value and the upper deviated DLCF (P < 0·05). In individuals with mandibular deviation, lip-closing force in the lower non-deviated direction was found to be smaller than the opposing lip-closing forces. When mandibular deviation was greater, the upper deviated lip-closing force was smaller.