The effect of lip augmentation on incisal display and lip projection

Objectives: The objective of the study is to quantify changes in maxillary incisor display on smiling (frontal view) and horizontal lip projection (profile view) following hyaluronic-acid lip augmentation. Material and Methods: Twenty-five healthy adult females underwent standardized hyaluronic-acid lip augmentation. Standardized frontal maximum-smile and right-profile photographs were obtained before treatment and at 2 weeks. A single calibrated investigator measured maxillary incisor display (vertical) and horizontal lip projection relative to the esthetic ricketts plane (E-Plane) and subnasale vertical line (SnV) using calibrated image-processing software. Pre–post differences and correlations/regressions were analyzed with parametric or non-parametric methods as appropriate; significance was set at 0.05 (two-tailed). Results: On average, upper lip coverage of maxillary incisors increased by 1.11 mm, upper-lip projection increased 1.26 mm (E-Plane) and 1.35 mm (SnV), and lower-lip projection increased 1.01 mm (E-Plane) and 1.44 mm (SnV) (all p < 0.001). Lower-lip projection to E-Plane correlated with filler volume, whereas upper-lip changes did not. Regression showed pre-injection incisor display predicted vertical upper-lip change, and pre-injection upper-lip–to-SnV distance predicted horizontal change after adjusting for filler volume. Conclusion: Hyaluronic-acid lip augmentation reduces maxillary incisor display on smiling and increases horizontal lip projection. Magnitude of change depends more on baseline soft-tissue position than on filler volume alone.