Color Stability of CAD/CAM Ceramics Prepared with Different Surface Finishing Procedures.

PURPOSE: To investigate the color stability of zirconia-reinforced lithium silicate glass-ceramic and lithium disilicate reinforced glass-ceramic, which were prepared with various surface finishing procedures, following 1-week, 2-week, 1-month, and 2-month storage in various beverages, and after the application of polishing paste. MATERIALS AND METHODS: Lithium disilicate glass-ceramic (IPS e.max CAD HT) and zirconia-reinforced lithium silicate ceramic (Vita Suprinity HT) CAD/CAM blocks were sectioned with a diamond saw (Metkon) under water cooling into 1.5 × 7 × 12 mm dimensions (N = 120). All specimens were polished with silicon carbide paper (600-, 800-, and 1200-grit) under water for 120 seconds. The specimens were prepared using 3 surface finishing procedures: glaze, mechanical polishing, and external staining and glaze in accordance with manufacturers' instructions. Then, each group was divided into 2 storage subgroups, black tea and coffee (n = 10/group). Color values were measured in CIELAB color space with dental spectrophotometer (VITA Easyshade) at the initial stage, and following 1-week, 2-week, 1-month, 2-month storage, and after fine-grit polishing paste application (Proxyt). Color changes (ΔE) were calculated and statistically analyzed using ANOVA followed by Bonferroni corrected post-hoc tests using Number Cruncher Statistical System 2007 (α < 0.05). RESULTS: For lithium disilicate glass-ceramic, glaze procedure showed statistically lower color change values than mechanical polishing and external staining and glaze surface finishing groups (p < 0.05) following storage in both beverages, whereas for zirconia-reinforced lithium silicate ceramic, glaze procedure showed statistically lower color change values than mechanical polishing, but statistically insignificant values with respect to external staining and glaze group, following storage in both beverages. Lithium disilicate glass-ceramic groups showed statistically lower or statistically insignificant color change values with respect to zirconia-reinforced lithium silicate ceramic groups, except for the external staining and glaze surface finishing group in coffee. Significantly lower discoloration values were obtained following polishing paste application, with respect to 2-month storage in beverages (p < 0.05). CONCLUSION: Glazing alone led to more color stability with respect to mechanical polishing and external staining and glaze for zirconia-reinforced lithium silicate and lithium disilicate glass-ceramic. Lithium disilicate glass-ceramic showed higher color stability compared to zirconia-reinforced lithium silicate ceramic. Polishing paste resulted in a decrease in discoloration to clinically acceptable values.

Effect of Veneering Methods on Zirconia Framework-Veneer Ceramic Adhesion and Fracture Resistance of Single Crowns.

PURPOSE: The aim of this study was to evaluate the fracture resistance (FR) and shear bond strength (SBS) via finite element analysis (FEA) of zirconia framework veneered with different methods. MATERIALS AND METHODS: Zirconia frameworks were prepared as crowns for FR and cubic blocks for SBS (N = 60, n = 10). The specimens were veneered with one of the following veneering methods: (a) overcemented file-splitting (OCF), (b) layering (L), or (c) overpressing (P). For crowns, stainless steel dies (N = 30; chamfer: 1 mm) were scanned using a contrast spray. Bilayered design for OCF and reduced design (1 mm) for both L and P were performed by computer-aided design and manufacturing. For the SBS test, zirconia blocks were sectioned (4 × 4 × 4 mm(3)) under water cooling and sintered. Frameworks were veneered with compatible ceramics for each veneering method and subjected to mechanical tests. The milled suprastructures were bonded to zirconia frameworks using a resin composite in Group OCF and photopolymerized. Crowns were cemented to the metal dies with resin modified glass-ionomer cement. All specimens were stored at 37°C, 100% humidity for 48 hours prior to mechanical tests. Data were statistically analyzed (ANOVA, Bonferroni tests, α = 0.05). Fractured specimens were examined under scanning electron microscopy (SEM), and FEA modeling of the crowns was performed. RESULTS: Mean FR values (N) were significantly higher with L (6102 ± 1519) and P (4117 ± 1083) than with of OCF (1900 ± 254) (p = 0.01). The mean SBS (MPa) in OCF (24 ± 4) was significantly lower (p < 0.002) than L (35 ± 6) and P (32 ± 6) (p > 0.05). For crown restorations, while only adhesive failures were found in OCF, cohesive failures within veneering ceramic were more frequent in P and L. FEA verified these findings. CONCLUSION: Veneering methods based on layering or pressing may reduce ceramic chipping but the overcemented file-splitting method does not seem to prevent this failure. CLINICAL SIGNIFICANCE: Layering and overpressing veneering methods on zirconia frameworks with reduced design might decrease chipping compared to overcemented file-splitting, where in the latter, zirconia framework and feldspathic suprastructure are combined using a resin cement.

Fracture strengths of endocrown restorations fabricated with different preparation depths and CAD/CAM materials.

The objectives of this study were to compare the fracture strength of endocrown restorations fabricated with different preparation depth and various CAD/CAM ceramics, and to assess the fracture types. Endodontically treated 100 extracted human permanent maxillary centrals were divided into two preparation depth groups as short (S: 3-mm-deep) and long (L: 6-mm-deep), then five ceramic subgroups, namely: feldspathic-ceramic (Vita Mark II-VM2), lithium-disilicate glass-ceramic (IPS e.max CAD-E.max), resin-ceramic (LAVA Ultimate-LU), polymer infiltrated ceramic (Vita Enamic-VE) and monoblock zirconia (inCoris TZI-TZI) (n=10/subgroup). The endocrowns were fabricated by CAD/CAM and were cemented with resin cement (RelyX U200). The teeth were thermally cycled (5,000cycles) and fracture tests were performed at 45º angle to the teeth. The data were statistically analyzed (Kruskal-Wallis, Mann Whitney U), failure modes were evaluated with stereomicroscopy. Zirconia group provided the statistically highest fracture strength, but also exhibited non-repairable failures. Preparation depth has an effect on the fracture strength only for feldspathic ceramic.