Method: The color parameters of 50 ceramic disks (10 mm diameter, thickness 0.3, 0.6, 0.9, 1.2, 1.5mm), (n=5), of IPS e.max® Press MO 0 and HO 0 (Ivoclar Vivadent) were evaluated upon samples of light cured composite material that simulate the shade of prepared teeth (IPS Natural Die Material Kit, Ivoclar Vivadent) (disks 10mm diameter, 5mm thickness). Saturated sucrose solution was interposed between the ceramic disks and the composite disks. Color parameters CIE L*, a*, b* were recorded with spectrophotometer VITA Easyshade® Advance, (VITA Bad Säckingen, Germany) in a viewing booth in D65 light (JUST LED Color Viewing Light, JUST Normlicht, Weilheim/Teck, Germany). L*, a*, b* values corresponding to the 0.3 mm thickness disk were considered as reference. The color differences (DE) were calculated between each thickness group and the reference (ΔE1- color difference 0,6mm-0,3mm thickness, etc.)upon each substrate. Data were analyzed statistically using univariate ANOVA tests and paired t-tests (α=0.05).
Results: Overall, there was a significant difference between ΔE values for a certain thickness group on all substrates, for both materials tested (p<0.001). However, when different thickness groups were compared among them, a significant difference was found only between ΔE1 and ΔE3, ΔE4 respectively (p<0.05). When the two opacities were compared, significant differences were found between each of the four thickness groups (p<0.01), MO showing higher values than HO (ΔE mean =3,42-6,43)
Conclusion: 1. Both types of materials have the capacity to mask underlying discolored substrates. 2. Masking increases with the increased thickness of the ceramic layer, all differences between thickness groups being higher than ΔE=3,5 acceptability threshold.