Effects of extraction of four premolars on vermilion height and lip area in patients with bimaxillary protrusion.

The purpose of this study was to evaluate the effects of orthodontic treatment, involving the extraction of four premolars, on vermilion height and lip area. Twenty-eight female patients (mean 21.9 ± 3.1 years) who were diagnosed with bimaxillary protrusion were selected for this study to be treated by extraction of four premolars. The control group consisted of 28 female volunteers (mean 25.0 ± 3.0 years) with Angle Class I normal occlusion. Frontal photographs of the patients were taken both before and after the orthodontic treatment in resting position. Thirty-five landmarks on the upper and lower lips were identified for the measurements of vermilion height and lip area. Lateral cephalograms were taken before and after active orthodontic treatment, and linear and angular measurements were performed. The mean pre-treatment values of vermilion height and lip area were significantly greater in the treatment group than those of the control group and decreased significantly after the orthodontic treatment towards the values in the control group. There were no significant differences in the vermilion height and lip area between the post-treatment and the control groups, except for lower lip area values. Significant correlations found between the changes in incisor position and the changes in vermilion height were few in number for the upper lip but greater in number for the lower lip. Thus, the results of this study show that bimaxillary protrusion cases can be treated by the extraction of four premolars to produce an aesthetic improvement in frontal facial features.