Mechanical properties-translucency-microstructure relationships in commercial monolayer and multilayer monolithic zirconia ceramics

Objectives: To evaluate the phase composition, microstructure, optical properties and mechanical properties of eight commercially available multilayer and monolayer monolithic dental zirconias. Methods: Five commercial 3Y-TZP (GC ST, GC HT [GC, Tokyo Japan]; Katana ML, Katana HT [Kuraray Noritake] and Lava Plus [3M Oral Care]) and three Y-PSZ (Katana STML, Katana UTML [Kuraray Noritake]; GC UHT [GC, Tokyo Japan]) zirconia ceramic grades were cut in plate-shaped specimens, sintered according to the manufacturer's instructions and mirror polished. The zirconia chemical composition was determined using X-ray fluorescence (XRF), phase composition was characterized using X-ray diffraction (XRD), while the grain size was measured using scanning electron microscopy (SEM). The translucency Parameter (TP) and Contrast Ratio (CR) were measured with a spectrophotometer (n = 10/group). The indentation fracture toughness (n = 10), Vickers hardness (n = 10) and biaxial strength (n = 20) of the sintered ceramics were assessed. The stress distribution during biaxial testing was assessed by Finite element analysis (FEA). Statistical analysis involved one-way ANOVA and post-hoc Tukey's HSD test and Pearson correlation test (alpha = 0.05). Results: FEA showed that the stress distribution in plate shape specimens was the same as for disks, rationalizing the use of plates for biaxial strength testing. As expected, higher quantities of Y2O3 were related to a higher cubic ZrO2 phase content and lower tetragonality t-ZrO2, which improved translucency but diminished flexural strength and toughness. While there was no significant correlation between grain size and other material properties, addition of pigments to the zirconia grade statistically negatively af-fected hardness. Conclusion: Even though an improvement in strength and translucency could be recorded for the last Y-TZP generation, future research still needs to strive for combined improve-ment of optical properties and mechanical reliability of zirconia ceramics. (c) 2022 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.

Automated summary

This study evaluated the composition, microstructure, optical properties, and mechanical properties of eight commercially available dental zirconias. The results showed that the chemical composition and grain size of the zirconia had an impact on its properties. Future research should focus on improving the optical properties and mechanical reliability of zirconia ceramics.