The influence of thickness and different resin cements on the flexural strength of high strength CAD/CAM glass ceramics

Objective: The aim of this study was to evaluate the influence of the thickness, etching, and resin cement type on the flexural strength of lithium disilicate-reinforced glass-ceramic (IPS e.max CAD, LD), and zirconia-reinforced lithium silicate glass-ceramic (CELTRA Duo, ZLS). ❧ Materials and Methods: IPD e.max CAD and CELTRA Duo CAD/CAM blocks were sectioned with a diamond-wafering blade, under constant water, to yield beams of varying thicknesses of 0.5 mm, 1.0 mm, and 2.0 mm. Specimens were polished, crystallized in a ceramic furnace, and sorted into different experimental groups (n=15) according to: ceramic material, thickness, etching, and luting cements (RelyX Unicem 2, Variolink Esthetic LC, and RelyX Luting Plus). The specimens were also tested at two different moments: 24 h and after 20,000 cycles of thermal fatigue. Flexural strength was assessed with three-point bending test, the values recorded in MPa. Statistical analysis was performed with t-test, two-way ANOVA, and Tukey post-hoc. ❧ Results: Statistically significant differences were found for LD, which yielded higher flexural strengths than ZLS, both before and after thermal fatigue. LD yielded higher flexural strength at 2.0 mm; all other thicknesses (0.5 mm, and 1.0 mm) were not significantly different (p>0.05). For ZLS, no significant difference (p>0.05) was identified in the flexural strength for any thickness tested. Different surface treatments did not produce statistical differences among the experimental groups (p>0.05). ❧ Conclusion: LD showed superior flexural strength results when compared to that of ZLS. Thickness did not influence the flexural strength for ZLS, whereas a 2.0mm thick specimens increased the flexural strength for LD. Etching improved the flexural strengths for ZLS. Different luting cements had no impact on the flexural strength of the two tested ceramics. ❧ Significance: Different CAD/CAM glass-ceramic yielded different flexural strengths. Thickness and infiltration of luting cements did not have an influence on the strength of the tested ceramics for ZLS. Higher flexural strength was observed for LD. Both CAD/CAM ceramic materials are suitable for minimally invasive restorations.