Methods: Ten bar-shaped specimens of four high-strength ceramics (n = 4x10) with different material composition and manufacturing methods had been broken in water in a three point bending test (IPS Empress 2, Ivoclar Vivadent; DC Zircon, DCS Dental AG; Lava, 3M ESPE; EZ A5, CeramTools). The fractured surfaces were inspected by light microscopy at several magnifications. Commonly used fractographic patterns for brittle materials, such as mirror, mist and hackle regions, were used to analyze and quantify the fractured surfaces of these specimens, and to detect the initiating site of the fracture. The analyses were performed twice at separate occasions by the same operator. Repeatability assessments of the measurements were performed using Kappa statistics. Correlations calculations was performed using Spearman's r.
Results: The initiating site was detected in all specimens, but initiating flaws were not always detected. The repeatability of the measurements of the different fractographic patterns varied among the materials. The repeatability of two independent measurements of mirror radii expressed by Kappa was between 0.48 and 0.61. Statistically significant correlations were found between mirror radii and force at fracture for the dental zirconia materials tested (rs=-0.9, p<0.01).
Conclusion: Fractographic analyses can be useful for assessing fracture modes and fracture initiating site of dental ceramics.
This work was supported with free material for specimens from 3M ESPE and Ivoclar Vivadent, and blanks at a reduced price from DCS Dental.