Abstract: Objective: To analyze the changes in the frontal morphology of lips during orthodontic treatment. Methods: Thirty-nine female patients (23.1±4.1) years who were diagnosed with bimaxillary protrusion were enrolled in the bimaxillary protrusion group. After the removal of the four first premolars, orthodontic treatment was performed with straight wire arch techniques. The control group consisted of 19 female volunteers (26.0 ± 2.6) years with class I individual normal occlusion. Facial photographs, intraoral images, and lateral cephalograms were taken before and after active orthodontic treatment in the resting position. Image pro-Plus 6.0 software was used to measure the vermilion height and lip area in the frontal photographs. Then incisors retraction and inclination were measured and the correlation of between incisors retraction and lip morphology were explored. Results: The vermilion height and lip area before orthodontic treatment in the bimaxillary protrusion group were significantly greater than the control group, and vermilion height as well as lip area was significantly reduced after orthodontic treatment. No difference in the upper lip area and vermilion height was observed between the patients with bimaxillary protrusions after treatment and the control group, whereas the area of the lower lip in bimaxillary patients after treatment was significantly larger than that of the control group. Orthodontic treatment significantly reduced the tooth inclination of patients with bimaxillary protrusion, and the incisor retraction was weakly correlated with the reduction of the vermilion height in the lateral medium. Conclusion: Lip morphology from the front view was significantly improved in bimaxillary protrusive patients by orthodontic treatment.

Key words: bimaxillary protrusion, orthodontic, vermilion height, lip area