Effect Of Ceramic Materials And Substrate Shades On Color Reproducibility Of Chairside CAD/CAM Crowns

Purpose.The aim of this study was to evaluate the influence of ceramic materials and substrate shades on the translucency,final color and shade reproducibility of chairside CAD/CAM crown restorations by measuring the chroma parameter of Chairside CAD/CAM ceramics over different shade substrates,and to guide the clinical application of chairside CAD/CAM ceramic materials.Methods.The A2-shade Chairside CAD/CAM ceramic blocks were cut into rectangular pieces（14×13mm）with the 1.1,1.6,and 2.1mm thicknesses using a low-speed precision sectioning cutter.The color measuring surface of ceramic pieces was sequentially polished with wet silicon-carbide paper.Then the ceramic specimens were sintered and glazed according to the manufacturer’s instructions.The 4 resin substrates were fabricated by the silicone rubber The resin was placed on the bonding surface of the resin substrate,and was polymerized by a light-polymerizing unit for 40s.Excess resin cement was removed with a slow hand-piece,and the cement layer was reduced and polished to0.1±0.02mm thick using 600 grit wet silicon-carbide paper.The Commission Internationale de l’Eclairage（CIE）values of ceramic specimens over 4 substrates（shade A2,A4,B3,and C4）,standard black and white tile were measured with a spectrophotometer.The translucency parameters（TP）and the color differences(ΔE₀₀values)between ceramic specimens and the Vita A2 shade tab were calculated.The analysis of covariance,and the post hoc Tukey HSD tests were used to analyze the data（α=0.05）.TheΔE₀₀ values were compared with the perceptibility thresholds(ΔE₀₀=1.25)and acceptability threshold(ΔE₀₀=2.23).Results.The 3-way ANOVA showed that theΔE₀₀ values were significantly affected by the ceramic type,ceramic thickness and substrate shade（P<0.001）.The 2-way ANOVA showed that ceramic type and thickness had a significant effect on TP values（P<0.001）.TheΔE₀₀ values ranged from 1.67 to 8.96,which were more than the clinically perceptible color threshold of 1.25.The acceptable color differences(ΔE₀₀<2.23)to the A2 shade tab were produced by e.max CAD HT and e.max CAD HT over substrate A2,as well as Empress CAD LT,2.0-mm Suprinity T,or e.max CAD LT over substrate B3,and Empress CAD LT over substrate A4.TheΔE₀₀ values of specimens over the substrate A4 and C4were all above the clinically acceptable threshold except for 2.0-mm-thick Empress CAD LT over substrate A4(ΔE₀₀>2.23).Conclusions.The color reproducibility of Chairside CAD/CAM crowns is influenced by the ceramic thickness and type.Compared to lithium disilicate glass-ceramic,zirconia-reinforced lithium silicate-based ceramics were better matched to the Vita A2 shade tab.All the Chairside CAD/CAM ceramics over the substrate C4 were unable to reproduce the color of the VITA A2 tab.