Effect of Different Surface Finishing Procedures on the Color and Translucency of two CAD/CAM Monolithic Glass Ceramics

Purpose: The purpose of this study was to investigate the effects of different surface finishing procedures, storage solutions, and prophylactic polishing on the color and translucency parameters (TPs) of two machinable glass ceramics; lithium silicate glass-ceramic (Obsidian)and lithium disilicate reinforced glass-ceramic (IPS e-max CAD).
Materials and Methods: Obsidian and e-max milling blocks were sectioned with a low speed cutting machineunder water cooling into square specimens (10×10×1 mm3)(N=60). The specimens were divided into 3 groups (n=10 each) according to the received surface treatment; finishing and polishing, glaze, and staining and glaze in accordance with manufacturers’ instructions. Then, each group was further subdivided into 2 storage subgroups, coffee and distilled water as a control (n =5 for each subgroup). Color and translucency values were measured in CIELAB color space with spectrophotometer at the initial stage, and following 18 days, and after fine-grit prophylactic polishing paste application. Color changes (ΔE) and translucency (ΔTPs) were calculated and statistically analyzed using One-way ANOVA for comparing surface treatment followed by Tukey’s pair-wise if showed significant. Student t-test was used within material type to show effect of staining. Multifactorial analysis of variance ANOVA was performed to detect significance between variables (material type, surface treatment, immersion solution and re-polish).
Results: There was a statistically significant difference between the ΔE values of both immersion solutions as (p = water) for both ceramics tested. Obsidian and e-max, glaze procedure showed lower color change values than finishing and polishing and staining and glazing surface(p > 0.05) following coffee storage. It was found that re-polish decreased color change significantly for both tested ceramics. The translucency was affected according the monolithic CAD/CAM ceramic type. The translucency of the e-max was found to be higher than that of obsidian glass-ceramic. Colorant coffee solution decreased the translucency of both obsidian and e-max ceramics. According to the results of this study, mechanical polishing exhibited highest translucency than stained and glazed and glazed groups. The re-polishing procedure decreased translucency parameter non-significantly for both tested ceramics.
Conclusions: Within the limitations of this study, the following conclusions could be drawn: Staining drinks as coffee had a negative effect on the color stability and translucency of both obsidian and e-max glass ceramic materials tested. Glaze procedure led to more color stability with respect to finishing and polishing and stained and glaze for both ceramics after 18 days coffee storage. Polishing paste led to a decrease in color changes for both ceramics tested. The translucency was affected according the monolithic CAD/CAM ceramic type. The translucency of the e-max lithium disilicate glass-ceramic was found to be higher than that of obsidian lithium silicate glass ceramic after different finishing procedure, after coffee storage and after re-polish. Finished and polished groups presented the highest translucency than stained and glazed and glazed for both ceramics tested. Re-polish decreased translucency parameters non-significantly for both tested ceramics.