Color match of machinable lithium disilicate ceramics: Effects of cement color and thickness.

STATEMENT OF PROBLEM: The effects of cement color and thickness on the color of machinable lithium disilicate (MLD) ceramic luted on metal foundation restorations is unknown. PURPOSE: The purpose of this study was to evaluate the effects of cement color and thickness on the shade matching of MLD restorations luted on silver-palladium (Ag-Pd) foundations. MATERIAL AND METHODS: Fifteen 1.5-mm-thick ceramic specimens were made from shade A1 LT lithium disilicate blocks. Five resin cements with different colors and opacities (Multilink Automix white opaque, Multilink Automix yellow, Nexus3 white opaque, Nexus3 white, Nexus3 yellow) of 3 thicknesses (300 µm, 100 µm, 50 µm) were sequentially luted to a roughened Ag-Pd alloy foundation restoration block. Five shade measurements were made with a portable spectrophotometer after optically connecting the ceramic specimen to each cement foundation block. The color differences (ΔE) between each specimen assembly and the target block (a 14×14×12-mm shade A1 LT crystalized e.max block) were recorded with the CIE (Commission internationale de l'éclairage) L*a*b* system. Clinical significance was determined by comparing color differences to perceptibility and acceptability thresholds with the 1-sample t test (α=.05). RESULTS: Both cement color and cement thickness significantly affected the mean values of the color difference (ΔE) of lithium disilicate ceramic assemblies to the target block (P<.001). Among the 5 cements tested, the lowest mean ΔE was observed for Nexus3 white opaque cement. Overall, the combination of Nexus3 white opaque cement and 100-µm thickness led to the lowest mean ΔE. The means of ΔE were below the clinically perceptible level (ΔE<2.6) for combinations of Nexus3 white opaque of 100-µm and 300-µm cement thicknesses (P<.001 and P=.022, respectively). The means of ΔE were below the clinically acceptable level (ΔE<5.5) for the following combinations: Nexus3 white opaque of 50-µm thickness, Nexus3 white, and Nexus3 yellow for all tested cement thicknesses and Multilink white opaque or Multilink yellow of either 50-µm or 100-µm cement thickness (P<.001). The means of ΔE were above the clinically acceptable level (ΔE>5.5) for Multilink white opaque and Multilink yellow of 300-µm cement thickness. CONCLUSIONS: The colors of machinable lithium disilicate ceramic restorations placed on Ag-Pd foundation were affected by both the color and thickness of cements. Among the 5 cements tested in this study, Nexus3 white opaque cement of 100 µm or 300 µm yielded shade matches below the clinical perceptible threshold (ΔE<2.6) relative to the target block.

Color match of machinable lithium disilicate ceramics: effects of foundation restoration.

STATEMENT OF PROBLEM: Metal or white opaque foundation restorations may negatively affect the color of machinable lithium disilicate (MLD) ceramic restorations. PURPOSE: The purpose of this study was to evaluate the effects of ceramic thickness and foundation restoration materials on the color of MLD restorations. MATERIAL AND METHODS: Forty-five ceramic slices in 3 thicknesses (1.0 mm, 1.5 mm, 2.0 mm; 15 slices in each group) were made from low-translucency (LT) shade A1 IPS e.max CAD blocks. Resin cement (Multilink yellow) of 100-µm cement thickness was bonded to 3 different foundation restoration materials: silver-palladium (Ag-Pd) (Albacast) alloy, Type III gold (Midas), and white opaque foundation resin (Paracore white) to make the cement-foundation blocks. After optically connecting each ceramic specimen to the cement-foundation block, the color of each laminated combination was measured with a portable spectrophotometer (Vita EasyShade Compact). The color differences (ΔE) between the specimen assemblies and a control target block (a 12×14×14-mm crystalized shade A1 LT e.max CAD block) were calculated. Two-way ANOVA and general linear model were used to assess the effects of ceramic thickness, foundation materials, and their interactions to the resultant ΔE (α=.05). Clinical significance was determined by comparing color differences to perceptibility and acceptability thresholds by using the t test (α=.05). RESULTS: Both ceramic thickness and foundation materials significantly affected the mean values of color difference (ΔE) of MLD restorations (P<.001). The mean value of ΔE decreased as the ceramic thickness increased. At a ceramic thickness of 1 mm, the color difference was above the clinically perceptible level (ΔE>2.6) with the 3 tested foundation materials (P<.001). As for the foundation materials, the ΔE was the lowest for Type III gold alloy, followed by Ag-Pd, then white opaque foundation resin. The color differences for Type III gold and a ceramic thickness of 1.5 or 2.0 mm were below the clinically perceptible level (ΔE<2.6) (P<.001). For Ag-Pd alloy or white opaque foundation resin, the color differences were above the clinically perceptible level (ΔE>2.6) (P<.001). Ag-Pd alloy reduced, the values of L* and b* parameters of MLD complexes, whereas the white opaque resin increased them. CONCLUSIONS: Based on the results of the study, the colors of MLD ceramic restorations were affected by both the ceramic thickness and foundation restoration materials. Increasing ceramic thickness improved the resultant shade matching. Ag-Pd alloy made the ceramic restorations darker and bluish, whereas white opaque foundation resin made restorations brighter and yellowish.