Relationships between fracture toughness, Y2O3 fraction and phases content in modern dental Yttria-doped zirconias

The relationship between fracture toughness and Yttria content in modern zirconia ceramics was revised. For that purpose, we evaluated here 10 modern Y2O3-stabilized zirconia (YSZ) materials currently used in biomedical applications, namely prosthetic and implant dentistry. The most relevant range between 2-5 mol% Y2O3 was addressed by selecting from conventional opaque 3 mol% YSZ up to more translucent compositions (4-5 mol% YSZs). A technical 2YSZ was used to extend the range of our evaluation. The bulk mol% Y2O3 concentration was measured by X-Ray Fluorescence Spectroscopy. Phase quantification by Rietveld refinement considered two tetragonal phases or an additional cubic phase. A first-account of the fracture toughness (K-Ic) of the pre-sintered blocks is given, which amounted to 0.4 - 0.7 MPa root m. In the fully-densified state, an inverse power-law behavior was obtained between K-Ic and bulk mol% Y2O3 content, whether using only our measurements or including literature data, challenging some established relationships. A linear relationship between K-Ic and the fraction of the transformable t-phase was established within the range of 30-70 vol%.