Contrast Ratios and Masking Ability of Three Ceramic Veneering Materials

MastersStatement of the Problem: Porcelain veneers are translucent materials and are therefore affected by the thickness of the porcelain used as well as the color of the underlying substructure which limits their masking ability and compromises the esthetic result in heavily stained teeth. Purpose: The purpose of this study was to compare the contrast ratio (opacity) and masking ability (△E) of three different veneering ceramics with two thicknesses 1.0 and 1.5 mm by measuring the color differences over white and black backgrounds. In addition, this study tested the correlation between contrast ratio and masking ability of these veneering ceramics. Methods and Materials: Thirty disk shaped specimens were fabricated from three types of all-ceramic systems: IPS e.max Press, Vita VM7 and Nobel Rondo Press Alumina Solo of shade A2. The disks were 12.0 mm in diameter and 1.0 mm, 1.5 mm thick. The contrast ratio (CR=Yb/Yw), defined as the ratio of illuminance (Y) of the test material when it’s placed on the black background (Yb) to the illuminance of the same material when it’s placed over a white background (Yw), was determined. The color (CIE L*a*b*) and illuminance (Y) of each specimen were measured over standard white and black tiles using a spectrophotometer with an aperture of 0.3 cm x 0.8 cm. For each of the ceramic discs, three measurements were made in three different locations around the center of the disc (n=15). Masking abilities of the specimens were determined by measuring the color difference (ΔE) over white and black backgrounds. Differences among the contrast ratios and masking abilities of the three materials with the two thicknesses were analyzed using Two-way analysis of variance (ANOVA). One-way analysis of variance was used to compare the mean values of contrast ratio across the three materials followed by Duncan multiple comparison test. The correlation between contrast ratio and masking ability as well as thickness and contrast ratio were determined by comparing R2 values (Square of coefficient of correlation) obtained from a linear regression analysis. For comparison of mean contrast ratio values, Student’s t-test for independent samples was used. Results: Contrast ratio values of Nobel Rondo were significantly less than those of IPS e.max Press and Vita VM7, whereas, the contrast ratio of IPS e.max Press was higher than Vita VM7. Furthermore, contrast ratio increased as the thickness of the discs increased to 1.5 mm for all three materials. The △ L*, △ a* and △ b* values decreased as the thickness of the ceramic discs increased from 1.0 to 1.5 mm for all ceramics tested. It was also observed that mean △E values were significantly higher with 1.0 mm thick discs than with 1.5 mm discs. Among the three materials Nobel Rondo had significantly higher △ L* values and lower △ a*. Also, Vita VM7 demonstrated significantly higher △ a* values when compared to those of IPS e.max Press. In addition, no significant difference was found in △ b* values between all three materials. It was observed that Nobel Rondo had the highest △E when compared to IPS e.max Press or Vita VM7, whereas the △E of the latter two were not significantly different from one another. There is a strong linear correlation between contrast ratio and masking ability. Conclusion: Contrast ratio and masking ability are affected by the type as well as the thickness of the ceramic used. IPS e.max Press and Vita VM7 are similar in their masking abilities, while Nobel Rondo had the lowest masking ability. Nobel Rondo was the most translucent followed by Vita VM7 while IPS e.max Press was the most opaque of the latter two. None of the materials tested was able to completely mask the black background. It is therefore recommended that the type of ceramic should be chosen according to each clinical situation