The lip sealing function correlates with increased facial height

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In this study, the lip sealing function was investigated in individuals with increased anterior facial height by mandibular clockwise rotation. Seven-teen adult volunteers with normal incisor relationship and without severe anterior crowding were divided into 9 competent and 8 incompetent lip subjects based on EMG activities of lower lip at rest with the lips in contact and apart. The inter-incisal distance was increased evey 2.0mm to 6.0mm with occlusal splint, while EMG activities of the lower lip were recorded. With increase of the facial height by 6.0mm, all subjects showed lip incompetence. EMG parameters of the lower lip correlated significantly with the facial height in two groups. The slope of regression line between the rate of EMG difference and the rate of facial height was significantly steeper in the competent lip group than in the incompetent lip group. For the competent lip group, the mean rate of EMG difference was positive value when increasing facial height by 2.0mm, however some of the competent lip subjects showed negative value. The results suggest that increased facial height by clockwise rotation of the mandible has significant effect on the lip sealing function in the competent lip subjects, and there seems to be threshold inducing lip incompetence according to the increased facial height.
日本矯正歯科学会の論文