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.

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.

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.