Fractographic and Microhardness Evaluation of All-Ceramic Hot-Pressed and CAD/CAM Restorations after Hydrothermal Aging.

All-ceramic dental restorations have great advantages, such as highly esthetical properties, a less complex fabrication, and a similar abrasion resistance to enamel. Despite these advantages, ceramic materials are more prone to fracture due to their brittle microstructure. The main aim of this in vitro study was to determine the difference in hot-pressed and milled glass-ceramic mechanical properties such as fracture resistance and microhardness (VHN). Four types of ceramics, two hot-pressed and two milled, feldspathic glass-ceramics and zirconia-reinforced glass-ceramics were selected in this study and tested using the static loading test and Vicker's testing. Hydrothermal aging, consisting of different baths with temperatures between 5 degrees Celsius and 55 degrees Celsius, was chosen as the in vitro aging method. Statistical analyses are performed using SPSS Statistics software at a significance level of p < 0.05. Micro-hardness values decrease after hydrothermal aging. The static loading test reveals a significant difference between the feldspathic hot-pressed glass-ceramic, which fractures at lower forces, and milled zirconia-reinforced lithium silicate glass-ceramic, which fractures at greater forces (N). Fractographic analysis of the fractured fragments resulted in the static loading test revealing different surface features about the crack origins and propagations under a stereomicroscope.