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

Metal or white opaque foundation restorations may negatively affect the color of machinable lithium disilicate (MLD) ceramic restorations.

The purpose of this study was to evaluate the effects of ceramic thickness and foundation restoration materials on the color of MLD restorations.

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).

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.

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.