The aim of this study was to evaluate the masking ability of a combined application of opaquers and resin composite over discolored backgrounds: A3, A3.5, C2, C3, and C4. The groups were divided according to the opaquer brand, the number of opaquer coats (one or two), and the thickness of the resin composite layer (0.5 or 1.0 mm). The color measurements were made by a reflectance spectrophotometer (SP60, EX-Rite). The color difference between the opaquer + resin composite + background and a reference background was calculated using the CIEDE2000 formula. ANOVA and Tukey's post hoc test (α=0.05) were used to analyze the ΔE00 mean values. A bivariate analysis was used to determine the association between dependent and independent variables. The masking ability was rated by the ΔE00 visual thresholds of acceptability and perceptibility (Excellent Match: ΔE00 ≤ 0.8; Acceptable Match: 0.8 < ΔE00 ≤1.8; Moderately Unacceptable Mismatch: 1.8 < ΔE00 ≤ 3.6; Clearly Unacceptable Mismatch: 3.6 < ΔE00 ≤ 5.4; Extremely Unacceptable Mismatch: ΔE00 > 5.4). The mean ΔE00 values ranged from 0.5 to 5.52. Masking ability was affected by the opaquer brand, thickness of the resin composite layer, and background shades. Most of the combinations that achieved either excellent or acceptable masking ability were obtained with combinations composed of one or two coats of opaquer and a 1.0-mm-thick resin composite layer for all backgrounds except C4. Acceptable results were also obtained for combinations with 0.5-mm-thick resin composite over C2, A3, and A3.5 backgrounds.
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