Measuring the Infinite Optical Thickness of Dentine Porcelain of the IPS E.max
Dentine porcelain disc specimens 13.0 mm in diameter with thicknesses of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0 mm, were made using IPS E.max color systems B, C, and D and their chromatic aberration values (ΔE) under the standard black background and the standard white background were measured using a Minolta CM-5 spectrophotometer. Then, the cubic regression formula of best fit was used to calculate the thicknesses of dentine porcelains of various color numbers at a ΔE of 1.0 and 1.5. The determination coefficient of the regression formula of color system B was 0.990–0.995, that of color system C was 0.989–0.997, and that of D was 0.993–0.998; and R2 is close to 1. The results show that the regression formulas of the 11 thickness groups have good fit. The infinite optical thickness values of the IPS E.max dentine porcelains were as follows: for B1–B4, 3.263–2.711 (ΔE = 1.0) and 2.910–2.493 (ΔE = 1.5); for color system C, 2.727–2.611 (ΔE = 1.0) and 2.473–3.365 (ΔE = 1.5); and for color system D: 2.928–3.694 (ΔE = 1.0) and 2.656–2.458 (ΔE = 1.5). When the chromatic aberration tolerance is 1.5, the thickness of dentine porcelain required to reach the infinite optical thickness is less than the numerical value at ΔE = 1.0. As the thickness increases, the influence of the background diminishes and the specimen looks truer to its inherent color. The results prove that thickness of dentine porcelain positively correlates with its masking ability and that its thickness must exceed its infinite optical thickness so that its color will not be influenced by the background color.
Yiwang Bao, Danyu Jiang, Li Tian and Jianghong Gong
L. Q. Shao et al., "Measuring the Infinite Optical Thickness of Dentine Porcelain of the IPS E.max", Key Engineering Materials, Vol. 492, pp. 349-353, 2012