The aims of this study were to evaluate the morphological changes in the lips and to determine the degree of improvement in the smile after mandibular advancement surgery for hyperdivergent retrognathism. The subjects were divided into two groups: one group consisted of 10 adult female patients who underwent mandibular advancement surgery and a control group that consisted of 30 adult female volunteers with normal occlusion. The data were collected from cephalometric radiographs and frontal photographs taken at pre- and posttreatment at the start of the pre-surgical orthodontic treatment and the completion of post-surgical orthodontic treatment. Conventional cephalometric variables as well as the coordinates of the reference points were calculated. Thirty-five landmarks were placed on each tracing made from the frontal photograph. Thereafter, the landmarks were digitized into an x- and y-coordinate system with the subnasal point as the origin. The comparisons between pretreatment and posttreatment at rest and on smiling, and the comparisons between the treatment and control group were made using the Wilcoxon matched-pairs and signed-rank tests and the rank-sum tests. In the pretreatment stage, both the upper and lower lips were positioned inferior in comparison to the control group at rest. The lower lip was positioned downward in the smile in the pretreatment group in comparison to the control group. These characteristics of the hyperdivergent retrognathism in the smile still remained after orthognathic treatment. These findings of this report are considered to be important because they demonstrate that these changes can be quantitatively and reproducibly analyzed.
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