Correlation Between Lip Prominence and Orthodontic Incisor Repositioning Within an Aesthetic Triangle Framework

Background and Objectives: Accurate prediction of lip prominence changes following orthodontic treatment remains challenging because traditional profile analyses rely on isolated reference lines that do not account for combined nasal and chin morphology. The aesthetic triangle framework integrates these structures and may provide a more comprehensive evaluation of lip position. Materials and Methods: This correlative clinical study evaluated 82 orthodontic patients undergoing bimaxillary incisor repositioning. Lateral cephalograms and standardized profile photographs were obtained before and after treatment. Lip position was assessed relative to the aesthetic triangle boundaries, and dentoalveolar changes were quantified using standard incisor measurements. Lip thickness was also analyzed as a potential modulating factor. Results: Mandibular incisor inclination demonstrated a moderate positive correlation with anterior displacement of the lower lip within the aesthetic triangle (Pearson r = 0.45, p < 0.01). Multiple linear regression analysis confirmed IMPA as a significant predictor of lower lip migration (β = 0.41), explaining approximately 21% of the observed variance (R² = 0.21). In contrast, maxillary incisor inclination (U1-SN) showed weaker and statistically inconsistent associations with upper lip position. Compartment analysis revealed that approximately 32% of patients exhibited anterior migration of the lower lip from the posterior to the central aesthetic triangle compartment following treatment. These findings suggest that mandibular incisor inclination exerts a measurable influence on lower lip prominence, whereas upper lip positional changes appear to be less directly related to maxillary incisor variables. Conclusions: The aesthetic triangle provides a clinically meaningful framework for interpreting orthodontic soft-tissue changes as spatial migration rather than isolated linear measurements. Lower lip prominence responds predictably to dentoalveolar mechanics, whereas upper lip position also depends on soft tissue morphology.