Does fast sintering affect the optical properties, fracture strength, and microstructure of monolithic zirconia?

The purpose of this study was to examine the influence of fast sintering on the optical properties, fracture strength, and microstructure of monolithic zirconia (MZ) ceramics. After 20 disc-shaped and 4 square-shaped samples from the MZ block were machined in the CAM device, groups were created by the sintering procedure in accordance with the manufacturer's recommendations: Standard (Grup S; disc-shaped n = 10 square-shaped n = 2) and fast (Grup F; disc-shaped n = 10 square-shaped n = 2). Then, hydrothermal aging was applied to all samples. To calculate translucency, opalescence, and fluorescence values, the LabCh color data of the samples were defined using spectrophotometers. The disc samples were biaxially fracture tested, and the values were determined. The chemical content, grain size (GS), and phase composition of the square-shaped samples were analyzed, respectively. Since the grain size did not conform to the normal distribution, the Mann-Whitney U test was used for statistical analysis, and all other variables were analyzed by an independent sample t test (α = 0.05). The sintering procedure affected translucency, opalescence, fracture strength, and GS significantly (P < 0.05), but not fluorescence (P > 0.05). While both groups had similar crystal structures, there were some minor differences in chemical content. All samples had a higher fracture strength than the ISO 6872 standard recommends. The sintering procedure had no clinically significant effect on the optical properties of MZ. The fast sintering procedure of MZ can be recommended.