Effect of ceramic type, cement shade, and ceramic thickness on the optical properties of the definitive restoration and the ability to mask a metal substructure

Abstract

Statement of problem

The influence of ceramic type, cement shade, and ceramic thickness on the final color of the restoration and its masking ability is unclear.

Purpose

The purpose of this in vitro study was to investigate the effect of the ceramic type and translucency parameters, ceramic thickness, and cement shade on the color of the definitive restoration and its masking ability.

Material and methods

A total of 120 ceramic specimens were fabricated in different thicknesses and divided into 10 groups: high translucency zirconia (HTZ 0.8, 1.2, 1.6 and 2 mm) (ZX2 98; Dental Direct), porcelain-fused-to-zirconia (PFZ1.5 and 2 mm) (DD Bio ZW iso color High Strength; Dental Direkt), monolithic low translucency lithium disilicate (LT 1 and 1.5 mm) (e.max; Ivoclar AG), bilayered glass-ceramic with a high opaque lithium disilicate (HO 1.5 and 2 mm) (e.max; Ivoclar AG). The color and translucency of the specimens were measured based on the L*a*b values and remeasured after applying resin cement evaluation pastes (Panavia V5 Try in paste; Kuraray Dental) in 3 colors: A2, opaque (O), or white (W) over 2 background materials (nickel chromium alloy or composite resin shade A2). The VITA Classic shade guide was used as the reference L*a*b value to evaluate the color matching capability of different ceramic-cement combinations. Color change (ΔE_ab) was measured, and the perceptibility threshold (PT) was set at 2.6 and the acceptability threshold (AT) at 5.5.

Results

The mean ΔE of the specimens ranged from 0.4 to 4.5. The type of ceramic significantly affected the color and translucency parameter (P<.001). In all groups, translucency decreased significantly with the increasing thickness of the ceramic (P<.001). According to the perceptibility threshold, the color of the nickel chromium background could be concealed by all 2 shades of cement (A2, opaque, and white). Nevertheless, the LT 1-mm, LT 1.5-mm, HTZ 0.8-mm, and HTZ 1.2-mm groups exhibited noticeable color changes when opaque cement was applied. Specimens with lower translucency parameters had better color matching with the A2 color. The HTZ 0.8-mm A2, LT 1-mm A2, and HTZ 0.8-mm W groups showed the least color match, with mean ΔE values of 12.4, 11.9, and 11.3, respectively. However, the PFZ 2-mm O and PFZ 2-mm W groups exhibited the best color match, with mean ΔE values of 1 and 1.4.

Conclusions

The thickness of the ceramic had a significant effect on its translucency. Moreover, the translucency of the ceramic influenced its masking ability and had a direct correlation with the color change in the presence of cement. Ceramic materials with an opaque framework had lower translucency but better color matching with the reference shade.