Shade Variation Influences Color Mismatch in CAD-CAM Lithium Disilicate Crowns Relative to Corresponding Shade Guide

To evaluate the influence of ceramic shade on color matching of CAD-CAM lithium disilicate (Li-disilicate) crowns relative to corresponding shade tabs, assessed based on Commission Internationale de l'Eclairage (CIE) values and nominal shade.

A cross-sectional study was conducted to determine the shades of CAD-CAM Li-disilicate crowns (VITA Classical shades A3, B3, C3, and D3; n=5 per shade) using a spectrophotometer, an intraoral scanner, and visual assessment by nine observers with varying dental experience. Crowns were cemented onto shade-matched abutment. Color differences (ΔEab and ΔE00) were measured with the spectrophotometer and compared with perceptibility and acceptability threshold. Trueness (%) of each method was calculated using the corresponding shade tab as the reference. Independent samples t-test and one-way analysis of variance were used to compare the CIE values of the crown samples and their corresponding shade tabs.

Shade C3 showed the highest mean ΔEab (3.42 ± 0.32), exceeding the 3.3 acceptability threshold. ΔE00 values exceeded acceptability threshold of 1.8 for A3 (1.91 ± 0.61), B3 (1.93 ± 0.38), and C3 (2.82 ± 0.42). The spectrophotometer achieved 100% for A3, while B3 and C3 showed 0% trueness across spectrophotometer and intraoral scanner. Shade determined by human showed the lowest intra- and inter-method reliability.

Shades of CAD-CAM Li-disilicate crowns influenced the degree of color mismatch, assessed by both CIE values and nominal shade. The greatest ΔE values were observed in shade C3 crowns, and the spectrophotometer showed the lowest trueness for shades B3 and C3 crowns, indicating inconsistency between CIE values and nominal shade.