Development of Facial Soft-Tissue Asymmetry During Growth: A Mixed-Longitudinal Three-Dimensional Study

Background/Objectives: Most healthy faces are mildly asymmetric, but how this asymmetry changes during growth and relates to facial size is unclear. We examined whether whole-face soft-tissue asymmetry increases as children grow and whether any increase simply reflects facial growth. Methods: We analysed 1014 three-dimensional facial scans of 377 children aged 6.0–18.8 years, followed for up to 3.2 years (median 2.0); the primary asymmetry analysis included 1003 scans of 376 children, after whole-face values with an isolated extreme point were set to missing. Asymmetry was the mean absolute perpendicular distance between the facial surface and its mirror image. Mixed-effects models separated within-child change from between-child differences. Repeat-capture reliability was not assessed. Results: Asymmetry increased by 3.2% per year within children entering at 11 years (95% confidence interval [CI], 2.2–4.1); older entrants were 2.7% more asymmetric per year of age (95% CI, 1.6–3.8). After adjustment for imaging session, the estimate was similar but imprecise (3.4%; 95% CI, −1.4 to 8.5). Facial size increased by 1.5% per year and asymmetry relative to size by 1.6%. Within children, asymmetry rose by about 1.7% for each 1% increase in facial size (exponent 1.73; 95% CI, 1.28–2.19); after adjustment for age this association was imprecise (0.89; 95% CI, −0.13 to 1.91), so the contributions of facial size and age could not be separated. Boys had 6.5% greater asymmetry; relative to facial size, 3.1% (95% CI, −2.0 to 8.6). Conclusions: On average, facial asymmetry increased modestly as children grew and increased relative to facial size over the observation period; whether this reflects facial enlargement itself or other age-related changes could not be determined. The estimated annual increase (about 0.013 mm) was below the residual variability between scans (about 0.04 mm); these population-level findings suggest that change cannot be detected in individual children, and individual monitoring and diagnostic thresholds require validated measurement.