Triple blind fractography study of yttria-stabilized zirconia thin-film-modified porcelain

Objective: To determine if experience and fractography methodology of examiners results in differences in fracture toughness estimation of thin-film modified glass-ceramic Methods: Glass-ceramic blocks (Empress CAD, Ivoclar Vivadent, Schaan, Liechtenstein) were cut into bars (2x2x15mm) and polished through 1200-grit using abrasive paper. One side of each bar was air-abraded (50μm alumina, 0.28MPa, 20s) and ultrasonically cleaned (acetone, 5min) before yttria-stabilized zirconia (YSZ) films were deposited using radio frequency magnetron sputtering. Bars were separated into five groups (n=12/group): Polished (Control-1), Polished and air-abraded (Control-2), YSZ film applied with no bias, YSZ film applied with 100W bias, and YSZ film applied with 150W bias. Bars were fractured in three-point flexure using an electromechanical testing machine in deionized water at 37°C. Four specimens per group were randomly selected and flaw size and fracture toughness of specimens was determined by three independent examiners using flexure strength data and fractography techniques. Differences in flaw size between examiners and groups were statistically analyzed using ANOVA (Tukey's test for multiple comparisons). Results: There was a significant difference in flaw size between groups for one examiner. There was a significant difference in flaw size in air-abraded and 150W bias groups between examiners. Conclusion: Statistically significant differences in fractographically-calculated flaw size values were observed between examiners. Experience and fractographic methods were shown to affect estimation of fracture toughness. Results indicate that strict fractography methodology protocols are important for accurately estimating fracture toughness.