Fracture toughness of dental zirconia before and after autoclaving

概要

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The purpose of this study was to evaluate the low temperature aging degradation (LTAD) of two types of zirconia through the determination of fracture toughness before and after autoclaving. The fracture toughness of yttria stabilized tetragonal zirconia polycrystals (Y-TZP) and zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite, so called NANOZR) were determined by Single Edge V-Notch Beam (SEVNB) method before and after autoclaving at 134°C for 5 h. The fracture surfaces were characterized by micro-X-ray diffractometry and micro-Raman spectroscopy. Mean fracture toughness of Y-TZP slightly decreased from 6.31 to 5.79 MPa·m1/2 with the autoclaving (p < 0.01). On the other hand, mean fracture toughness of NANOZR showed no change as 11.03 MPa·m1/2 (p > 0.1) and was 1.75–1.91 times larger than that of Y-TZP. It seems to be caused by that NANOZR is susceptible to stress-induced transformation from tetragonal to monoclinic, but quite stable against LTAD.