Three-dimensional analysis of lip changes in response to simulated maxillary incisor advancement

Objective: To assess the immediate response of lips in three dimensions (3D) resulting from simulated maxillary incisor advancement. Materials and Methods: Incremental maxillary incisor advancement was simulated by placing wax of increasing thickness (þ2 mm, þ4 mm, þ6 mm) on the incisors of 20 participants, and the induced lip changes were recorded using 3D stereophotogrammetry. The induced displacement of lip landmarks was quantified using 3D image analysis software. Data were analyzed using a repeated-measures analysis of variance (ANOVA) after adjusting for age and sex of the study participants. Results: A large interindividual variation in lip response to simulated incisor advancement was observed. A significant overall effect on 3D lip changes was found for increasing values of simulated incisor advancement (F ¼ 13.2; P, .001) as well as significant differences between anatomical landmarks of the lip (F ¼ 7.4; P, .01). Most points moved outward and anterosuperiorly, except the midpoint and corners of the lip. Greatest movement was observed in the sagittal plane, followed by the vertical and transverse planes. Conclusions: Maxillary incisor advancement significantly affects upper lip change in three planes of space: particularly the anteroposterior plane, in which the response to simulated advancement appears to be nonlinear.