Microstructural changes and fracture resistance of nano-crystalline monolithic zirconia restorations upon aging

Abstract

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.