Impact of sintering speed and surface finishing on translucency, mechanical, microstructural and surface properties...

The aim of this study was to evaluate the effects of sintering speed and surface finishing on the optical, mechanical, microstructural, and surface properties of monolithic zirconia ceramics with different yttria content.

Three different zirconia materials (Katana UTML, Katana STML, DD Cube Bio ZX²) were subjected to either speed or conventionally sintering, followed by the application of various surface treatments. Translucency parameters were measured before and after aging. The biaxial flexural strength was measured after aging. The microstructure of the specimens was examined using scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses, while the surface roughness was analyzed using atomic force microscopy (AFM). Statistical analysis of the data was performed using three-way ANOVA, one-way ANOVA, the Kruskal-Wallis test, and Bonferroni post hoc comparisons.

The applied sintering speed, clinical adjustment, and aging processes did not produce a statistically significant effect on flexural strength (p = 0.245) or translucency (p = 0.478). The phase content of Katana UTML was not influenced by sintering speed or clinical adjustment either before or after aging. For the Katana STML material, phase content was unaffected by sintering speed and clinical adjustment prior to aging, but the monoclinic phase was detected in the structure after aging. In the DD Cube Bio ZX² material, the monoclinic phase was observed both before and after aging, and the proportion of the monoclinic phase increased after aging. SEM analysis revealed that speed sintering reduced the average grain size of monolithic zirconia. AFM analysis indicated that, after aging, the glazed samples of Katana UTML and Katana STML exhibited smoother surfaces compared to the grinding and polishing groups of the same materials. Furthermore, the speed sintering of DD Cube Bio ZX² material resulted in the formation of a more homogeneous surface. The increase in yttria content in the material decreased flexural strength and the amount of monoclinic phase formed after aging while increasing translucency, grain size, and the proportion of the cubic phase (p = 0.000).

Speed sintering, surface finishing, and aging did not significantly affect the translucency or flexural strength of monolithic zirconia. Polishing kits designed for zirconia can be used after speed sintering. Higher yttria content improved translucency, grain size, cubic phase, and aging resistance, but reduced flexural strength and monoclinic phase after aging.