Comparison between different fracture toughness techniques in zirconia dental ceramics

Vickers indentation (IF) and single-edge-V-notched beam (SEVNB), to measure the fracture toughness (K_IC ) of zirconia-based dental ceramics and mathematical models were proposed to establish a correlation between both. Zirconia (ZrO₂ ) stabilized with 3 mol. % of Y₂ O₃ (3Y-TZP) and 5 mol% of Y₂ O₃ (5Y-PSZ) were compacted (n = 42) and sintered for 2 h at different temperatures (1475°C, 1500°C, 1550°C, or 1600°C). After sintering, they were characterized by relative density using the ASTM C373-88 standard, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average grain size was measured according to the ASTM E1382-97 standard. The fracture toughness (K_IC ) was determined using two methods: Vickers indentation fracture toughness (K_IC-IF ): method based on mathematical modeling that considers the parameters used for the Vickers hardness test and Fracture toughness by the single-edge-V-notch-beam (K_IC-SEVNB ): method proposed by ISO 23146:08. The main phases of the 3Y-TZP and 5Y-PSZ ceramics were ZrO₂ -tetragonal and ZrO₂ -cubic, respectively. The 3Y-TZP specimens showed equiaxed grains with average grain sizes ranging from 0.55 to 0.79 μm. The grain sizes of 5Y-PSZ of specimens sintered at 1475°C and 1600°C were 0.62 and 2.32 μm, respectively. For all ceramics the crack size ratio was c/a < 2.5, suggesting a Palmqvist-type crack system. The fracture toughness measured by the Vickers indentation method (K_IC-IF ) and by the SEVNB method (K_IC-SEVNB ) was the same when the experimental data were fit to a mathematical model.