The increased patients demand to improve their dental esthetics has led to the development of new tooth-colored ceramic restorations; however, accurate color matching of the restoration to the adjacent teeth and the subsequent dentist-laboratory communication remain one of the most critical procedures in clinical dentistry. (1,2) Several factors influence the esthetic success of dental ceramic restorations, (3) such as surface or substrate characteristics, (4,5) marginal accuracy, (6) ceramic thickness, (7) translucency, (8) underlying
To assess the effect of nano-modification of two CAD/CAM monolithic Zirconia systems (wet and dry-milled) on microstructural changes and fracture resistance upon aging. Twenty monolithic Zirconia discs (10mm x1.5mm) were divided into 2 groups (n=10) according to fabrication system;wet-milled (Incoris TZI) and dry-milled (CeramillZolid). Each group was subdivided into two subgroups (n=5), whether subjected to aging or not. Aging proceduresincluded accelerated hydrothermal aging and cyclic loading. Microstructural changes were assessed quantitatively and qualitatively using x-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Discs were subjected to fracture resistance test usinguniversal testing machine. Meansandstandard deviations were recorded for phase transformation (t-m)of Zirconia and repeated ANOVA was used to correlate phase transformation with fracture resistance results (p≤0.05). For aged subgroups, XRD analysis revealed significantly higher phase transformation of wet-milled than dry-milled (p≤0.05) and SEM analysis revealed wide zone phase transformation for wet-milled zirconia and minimal zone for dry-milled. For both systems, no significant difference between the mean flexural strength values ofnon-agedand aged zirconia (p≤0.05). Nanocrystalline microstructure of monolithic zirconia improved its resistance to aging. The fracture resistance of the two systems was not affected by aging.
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