Effects of fabrication and shading technique on the color and translucency of new-generation translucent zirconia after coffee thermocycling.

STATEMENT OF PROBLEM: The color stability and translucency of preshaded and externally shaded monolithic and veneered new generation translucent zirconia are not well known. PURPOSE: The purpose of this in vitro study was to investigate the effect of fabrication (veneered or monolithic) and shading (preshaded or externally shaded) techniques on the color and relative translucency of translucent zirconia after coffee thermocycling. MATERIAL AND METHODS: Specimens of different thicknesses (0.5 mm for veneered and 1.5 mm for monolithic) were sectioned from preshaded and externally shaded translucent zirconia. Externally shaded specimens were colored by using the dipping technique. Externally shaded (Ext Mono) and preshaded (Pre Mono) monolithic zirconia specimens were sintered and glazed. Externally shaded (Ext Vene) and preshaded (Pre Vene) 0.5-mm-thick specimens were sintered, veneered with feldspathic porcelain (1 mm), and glazed. The color coordinates of specimens were measured with a spectroradiometer before and after 10 000 thermocycles in coffee solution. Color differences were calculated using CIEDE2000, and relative translucency parameter (RTP) values were calculated using the RTPCIEDE2000 formula. Analysis of variance (ANOVA) was used to analyze the CIEDE2000 color differences and RTP values (α=.05). RESULTS: Shading technique had a significant effect on the color difference values (P=.018). For the translucency data, the 3-way ANOVA revealed a significant interaction between the fabrication technique and shading technique (P=.002). Each pair of material subgroups within each combination of fabrication technique and shading technique was found to have a significantly different RTP, except between Ext Vene and Pre Vene (P=.115). CONCLUSIONS: Externally shaded translucent zirconia had a greater color change in coffee than the preshaded translucent zirconia, either in monolithic or veneered form. Fabrication technique significantly affected the RTP, and the monolithic zirconia was more translucent than the veneered zirconia.

Effect of surface treatments and coffee thermocycling on the color and translucency of CAD-CAM monolithic glass-ceramic.

STATEMENT OF PROBLEM: The effects of surface treatments and coffee thermocycling on the color and relative translucency of a recently introduced computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic glass-ceramic are unknown. PURPOSE: The purpose of this in vitro study was to evaluate the effect of coffee thermocycling on the color and relative translucency parameter (RTP) of CAD-CAM monolithic glass-ceramics after different surface treatments. MATERIAL AND METHODS: Specimens (1.5-mm-thick) were sectioned from zirconia-reinforced lithium silicate glass-ceramic (ZLS) (n=18) and lithium disilicate glass-ceramic (LDS) blocks (n=18). Two different types of surface treatments (glazing or polishing) were applied to the specimens. The specimens were subjected to 5000 thermocycles in a coffee solution. The color coordinates of specimens were measured before and after coffee thermocycling by using a spectroradiometer, and color differences and relative translucency values were calculated by using CIEDE2000 color difference and RTP formulas. ANOVA was used to analyze the color difference and relative translucency values by using maximum likelihood estimation and the Satterthwaite degrees of freedom methods. Any significant interaction between surface subgroups was further analyzed by using the Tukey-Kramer adjustment (α=.05). RESULTS: Material type had a significant effect on color difference (P=.018). All color difference values of all materials were smaller than the clinical acceptability threshold (<1.8 units). For relative translucency, material (P<.001) and coffee thermocycling had a significant effect (P=.014), and an interaction was found between the surface treatments and materials (P<.001). The Tukey-Kramer test revealed significant differences between glazed and polished subgroups of LDS material, except for ZLS-glazed and ZLS-polished subgroups. CONCLUSIONS: Different surface treatments of CAD-CAM monolithic zirconia-reinforced lithium silicate and lithium disilicate glass-ceramics resulted in clinically acceptable color changes after coffee thermocycling. The color changes in all groups, except for LDS-polished, were not perceivable. Lithium disilicate was more translucent than zirconia-reinforced lithium silicate before and after coffee thermocycling. Coffee thermocycling decreased the translucency of both of the materials. Different surface treatments affected the translucency of only lithium disilicate for tested thickness.

Effect of shading technique and thickness on color stability and translucency of new generation translucent zirconia.

OBJECTIVE: To evaluate the effect of shading technique and thickness on the color stability and translucency of translucent zirconia after coffee thermocycling. METHODS: Specimens in different thicknesses (1; 1.5; 2 mm) (n = 4 for each thickness) were sectioned from translucent preshaded zirconia (Pre) and externally shaded zirconia (Ext). After sintering, specimens were glazed and subjected to 10,000 thermocycling in coffee solution. The color coordinates of specimens were measured with a spectroradiometer before and after coffee thermocyling. Color differences and relative translucency parameter (RTP) values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze the CIEDE2000 color difference and RTP values (α = 0.05). RESULTS: According to 2-way ANOVA, no significant effect of shading technique and thickness on the color difference values was found (P > .05). According to 3-way ANOVA, a significant interaction between the shading technique and thickness (P < .0001) was found for RTP. The RTP parameter decreased with the increase in the thickness. Ext specimens presented significantly higher RTP than Pre specimens (P < .0001), except for between Ext 1 mm and Pre 1 mm (P = .179). CONCLUSIONS: Neither shading technique nor tested thicknesses affected the color of translucent zirconia. Shading technique and thickness affected the RTP of translucent zirconia. The RTP was inversely affected with the thickness of the material. Externally shaded zirconia presented higher RTP than preshaded zirconia for specimens thicker than 1 mm. CLINICAL SIGNIFICANCE: Discoloration with coffee was insignificant for the tested translucent zirconia in tested thicknesses (1, 1.5, 2 mm). When a translucent restoration is intended, thinner externally shaded translucent zirconia restorations should be preferred instead of preshaded translucent zirconia.

Effect of thickness on optical properties of monolithic CAD-CAM ceramics.

OBJECTIVE: To compare the effect of material and thickness on the color stability and relative translucency parameters (RTP) for monolithic ceramics subjected to coffee thermocycling. METHODS: Four specimens each at thicknesses of 0.5, 0,7 and 1 mm were sectioned from monolithic ceramics [preshaded monolithic zirconia (MonZr), lithium disilicate (LDS) and zirconia reinforced lithium silicate (ZLS)]. The specimens were glazed and subjected to 5000 coffee thermocycling. The color coordinates of specimens were determined with a spectroradiometer and color differences and RTP values were calculated with CIEDE2000 color difference and TPCIEDE2000 formulas. ANOVA was used to analyze CIEDE2000 color difference and RTP values (α = .05). RESULTS: For the color difference data, the 2-way ANOVA revealed a significant interaction between material and different thickness (P = .002). Except for 0.5 mm thick ZLS material, all materials in all thicknesses studied presented color changes within the clinically acceptable limits after coffee thermocycling. For the RTP data, the 3-way ANOVA revealed a highly significant interaction between material and different thicknesses (P < .001). CONCLUSIONS: Material type and thickness can be expected to affect color change and relative translucency of the restorations made with preshaded MonZr, LDS and ZLS materials. Except for 0.5 mm thick ZLS material, color changes of all studied materials were within the clinically acceptable limits. Except ZLS material, color changes of other materials were not significantly affected by thickness. Staining in coffee was not found to affect translucency, and the materials' translucency parameters were ranked from high to low as LDS, ZLS and MonZr at each thickness studied.

Evaluation of the topographical surface changes and roughness of zirconia after different surface treatments.

The purpose of this study was to investigate the surface morphology and roughness of zirconia after different surface treatments. Eighty sintered zirconia specimens were divided into four groups (n = 20) according to the surface treatments received: no treatment, erbium:yttrium-aluminum-garnet (Er:YAG) laser irradiation (400 mJ, 10 Hz, 4 W, 100 MPS, distance: 1 mm), tribochemical silica coating with 30 µm aluminum oxide (Al(2)O(3)) modified by silica, and air abrasion with 110 µm Al(2)O(3) particles. After the surface treatments, the surface roughness (Ra in µm) of the specimens was evaluated using a surface texture measuring instrument. Surface morphology of a specimen from each group was evaluated with atomic force microscope (AFM) and scanning electron microscope (SEM) analyses. The surface roughness values were statistically analyzed by the Kruskal-Wallis and Mann-Whitney U tests (p = 0.05). All of the surface treatments produced rougher surfaces than the control group (p < 0.005). While there were no significant differences between the surface roughness of laser and silica groups (p > 0.05). SEM and AFM analyses revealed changes in surface topography after surface treatments, especially in the laser group with the formation of rare pits and in the silica and air abrasion groups with the formation of microretentive grooves. According to the results of the statistical and microscopic analyses, all of the surface treatments can be used for roughening zirconia prior to cementation; however, air abrasion is the most effective surface treatment to obtain micromechanical retention.