Energy for fracture of a multilayered dental zirconia under mixed-mode testing

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© 2025 The Author(s). Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of The American Ceramic Society.Graded multilayer zirconias exhibit a microstructural gradient based on yttria content, but the transition zone between layers remains poorly characterized. This study evaluated the fracture energy required to create new surfaces in multilayer zirconias. Brazil-nut specimens were tested under different loading angles to induce tensile, shear, or mixed failure modes, using 3Y-TZP and 5Y-PSZ as controls. Groups were defined by zirconia type, loading angle, and hydrothermal aging. Fractured specimens underwent fractographic analysis, failure classification, scanning electron microscopy, and energy-dispersive X-ray spectroscopy characterization. Two-way analysis of variance revealed significant differences between loading angles but not aging. At 25°, where shear forces predominated, fracture energy was significantly higher [baseline: 964.74 (± 202.43); aged: 1389.12 (± 978.47) N/m] compared with most groups, except 15°. Multilayer zirconia showed intermediate fracture energy values between 5Y-PSZ and 3Y-TZP. Importantly, the transition zone presented a heterogeneous interphase rather than a smoothly graded structure. Shear stresses required higher energy release than tensile stresses. These results reveal the microstructural discontinuity and distinct fracture behavior of multilayer zirconias, providing new insights into the structure–property relationships of this class of ceramics.

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