Рurроse: To evaluate the influence of thermocycling on the microstructural, physical, and color stability of three CAD/CAM ceramic materials. Materials and Method: In total, 93 specimens (7×5×1.5mm) were prepared from lithium disilicate glass ceramic (IPS e.max CAD), Extra translucent zirconia (VITA YZ), and resin nanoceramic (Cerasmart 270). All the materials was A2 or equivalent shades. The samples were obtained as directed by the manufacturer. these were samples exposed to thermocycling at 5 to 55 C in distilled water for (10.000 cycles). Color stainability, surface roughness, microhardness and surface microstructure were measured and assessed prior and after thermocycling. The Statistical analysis were performed with a Wilcoxon Signed Ranks Test, independent Kruskal-wallis test and Pearsons’s correlation analysis. The significant level was set at P ≤ 0.05. Results: prior and after hydrothermal aging Cerasmart presented the lowest hardness value . VITA XT exhibited the highest hardness value . The surface roughness had the maximum level of exhibition in VITA XT group . lithium disilicate exhibited the lowest surface roughness values . Cerasmart showed the highest color changes values (∆E) after hydrothermal aging , lithium disilicate showed the lowest (∆E) values . after the hydrothermal aging the hardness of VITA XT increased significantly . surface roughness of lithium disilicate increased significantly after aging . for stain ability all the materials used in this study was within the clinically accepted threshold < 3.3 . Conclusion: Cerasmart showed least degree of hardness before and after aging and highest stainability after aging . Before and after aging, VITA XT showed the highest levels of hardness and surface roughness. lithium disilicate presented the lowest stainability , lowest surface roughness prior and after aging .
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