Influence of tooth color value and gingival display on smile attractiveness rated by laypersons, general dentists, prosthodontists, and orthodontists: a cross-sectional image-based observational study

To evaluate the interaction between tooth color value and gingival display in smile attractiveness ratings by laypersons, general dentists, prosthodontists, and orthodontists. Sixteen images combined four gingival-display levels (0, 1, 3, and 5 mm) with four simulated tooth shades (0M1, 1M1, 3M1, and 5M1). Forty observers in each of four groups rated all images on an 11-point numerical scale using the same device. Gaussian generalized estimating equations with bias-corrected covariance, Holm-adjusted comparisons, and repeated-measures sensitivity analyses were used (α = 0.05). The 160 observers provided 2560 ratings. Shade-by-gingival-display and three-way interactions were significant (both p < 0.001) and supported by sensitivity analyses. Lighter shades received higher ratings at 0 and 1 mm. At 3 mm, 1M1 exceeded 0M1 by 1.33 points (95% confidence interval, 1.12–1.54; adjusted p < 0.001). At 5 mm, 3M1 exceeded the other shades by 0.29–0.40 points (adjusted p ≤ 0.011). One observer-group pairwise comparison remained significant after multiplicity adjustment. The association between simulated tooth shade and smile attractiveness depended on gingival display. Lightness was not isolated from chromatic variation, and clinical generalizability requires further investigation. These image-based findings may inform discussion of tooth color and gingival display during esthetic assessment. They do not demonstrate a clinical benefit of whitening for excessive gingival display.