Effect of Chemical Corrosion & Roughness on Color of Veneering Ceramics

Objectives:To compare the effect of chemical corrosion, surface finishing methods and surface roughness on color of different veneering ceramics. Materials&Methods:Twenty ceramic disks (8x2mm) were fabricated (Empress II, Zirkonzahn, Noritake CerabienZR, Vita VM7, Finesse) in a special mold and divided into 2 groups of autoglaze and polishing(n=10). Surface roughness (Ra) of each specimen was evaluated using a profilometer (Mitutoyo-SJ201) before and after corrosion tests. The specimens were then subjected to in vitro corrosion (pH4,5-pH7-pH9 in water at 37 ± 2°C for 18h and 4% acetic acid solution pH=2,4 at 80 ± 2°C for 18h). Color measurements were made using a spectrophotometer (Vita-easyshade)according to the CIE L*a*b* color system. Color differences between polished and autoglazed groups, corroded at different pHs, were calculated. The data were statistically analyzed by ANOVA and TukeyHSD test (α=0.05). Multiple comparisons of Ra between pH groups of each ceramic were computed by t-test. Scanning Electron Microscopy(SEM) was performed before and after corrosion tests. Results:Ra values were significant among ceramic groups at different pH values (p<0.05). All groups demonstrated a smoother surface (Ramean=0,36±0,14) or just a minor increase in surface roughness. SEM also revealed smoother surfaces. No statistically significant difference was found between C,H,a,b parameters (P>.05) while difference for L and Ra values was significant between autoglaze and polishing groups (P<.05). Surface techniques significantly affected the color parameters of ceramics(P <. 001). The ΔE values ranged from 1.03 to 3.36. No significant relationship were found between Ra values and the color parameters of subgroups. Conclusion: Color parameters of ceramic material could be changed depending on surface finishing methods and abrasiveness of chemical medium. The rate of color change also depends on the brand of ceramic material. Ceramics are known to be durable and inert but oral conditions have great effect on their survival.