Core-Veneer Thickness and Translucency Influence on Lithium Disilicate Color

Objectives: To compare three different techniques (layering, cutting-back and staining) of two translucencies high (HT) and low (LT) in terms of color differences for IPS e.max Press (Ivoclar Vivadent, Schaan, Liechtenstein) lithium disilicate glass ceramics shade A1.
Methods: Lithium disilicate glass ceramic discs (n= 10/group) of the two translucencies were fabricated with 12mm diameter and 1.5mm thickness using different core & veneer thickness IPS e.max Press, shade A1. Six experimental groups were evaluated in terms of color differences: groups HT5 and LT5 with 0.5mm core + 1mm veneer thickness; groups HT10 and LT10 with 1mm core + 0.5mm veneer thickness; groups HT15 and LT15 with 1.5mm monolithic without receiving any veneer. Color differences were measured using a Crystaleye (Olympus, Tokyo, Japan) spectrophotometer. 2 independent-samples t-tests were used for the comparison of the translucency at 1mm and 1.5mm core thicknesses and a non-parametric test (Mann-Whitney U) test at 0.5mm core thickness. Non-parametric (Kruskal-Wallis) tests were used for the comparison of the thicknesses at each translucency, and Mann-Whitney U tests with Bonferroni correction were used as post-hoc tests.
Results: There was a statistically significant difference between the two translucencies at 0.5mm, 1mm and 1.5mm core (p<.001). For each translucency, 0.5mm core thickness showed the highest color difference (ΔE). For each core thickness, the HT groups showed higher ΔE compare to the LT groups. All post-hoc tests were significant (p ≤ 0.004).
Conclusions: Within the limits of the present study, the level of translucency and the different core-veneer thickness significantly influenced the color of lithium disilicate glass ceramic shade A1. Increasing the veneer thickness will lead to greater difference in color. Increasing the core thickness will lead to lower the color difference. Even with a slightly color difference in substructure LT ingots are highly recommended to be use.