Refractive Index and Translucency of Contemporary Esthetic Resin Composites Relative to Human Enamel: An In Vitro Study

Background/Objectives: Reproducing enamel optical behavior requires appropriate refractive and translucency characteristics. This in vitro study compared the effective group refractive index (RI) and visible translucency of five resin composites with human enamel and assessed whether the two optical properties corresponded. Methods: Sixty 1 mm specimens were evaluated across six groups (n = 10 each): Filtek Easy Match, Tetric EvoCeram, Estelite Sigma Quick, Charisma Diamond ONE, Harmonize, and human enamel. Effective group RI was measured at 1310 nm using optical coherence tomography. CIELAB coordinates were recorded over white and black backgrounds, and CIEDE2000 (TP00) and CIELAB (TPaβ) translucency parameters were calculated. Heteroscedasticity-robust models with Holm-adjusted composite-versus-enamel contrasts were used. Results: Enamel had a mean RI of 1.628 and TP00 of 15.76. All composites had lower RI values than enamel (adjusted p < 0.001). TP00 did not differ significantly from enamel for Filtek Easy Match, Tetric EvoCeram, or Charisma Diamond ONE, whereas Estelite Sigma Quick and Harmonize had lower TP00 values (adjusted p = 0.012 and 0.018). RI was not independently associated with TP00 after adjustment for material (p = 0.352). Conclusions: None of the composites reproduced enamel RI, while visible translucency was material-dependent and was not explained by effective group RI alone.