Importance of the vertical incisor relationship in the prediction of the soft tissue profile after Class III bimaxillary surgery

OBJECTIVE: To quantify the relative soft tissue profile response to the skeletal changes resulting from bimaxillary surgery to correct Class III malocclusion in patients with different vertical incisor relationships presurgery. MATERIALS AND METHODS: The sample comprised lateral cephalograms of 80 consecutive patients before and 2 months after surgery. All patients had one-piece Le Fort I and bilateral sagittal split osteotomies. Patients were divided in three subgroups according to their preoperative characteristics, as follows: (1) open-bite patients, (2) patients with positive overbite and the upper lip resting on upper incisors, and (3) patients with positive overbite and the upper lip resting on lower incisors (lip-block). Trimmed means of soft to hard tissue ratios were calculated for the subgroups. Regression analyses were performed to examine factors influencing the soft tissue changes. RESULTS: There were strong correlations between the horizontal movement of upper incisors and upper lip in patients with open bite (r = 0.77) and in patients with positive overbite and upper lip resting on upper incisors (r = 0.85). The upper lip followed the maxilla with a ratio of 0.5∶1. In patients with lip-block, the association between maxillary repositioning and upper lip changes was weak. In all groups a strong association between horizontal soft and hard tissue changes was observed for the lower lip and chin, but the pattern differed depending on the vertical movement of the mandible. CONCLUSIONS: In the prediction of soft tissue response it is important to take into account the vertical incisor relationship, particularly in patients with lip-block.