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Effects of surface treatments on the susceptibilities of low temperature degradation by autoclaving in zirconia.

The aim of this study was to investigate the effect of surface treatments on the aging susceptibilities by autoclaving in zirconia ceramics. Four commercially available tetragonal zirconia polycrystals and one zirconia-alumina composite were tested. Disk-shaped specimens were prepared and the grain sizes were analyzed using a scanning electron microscope and image analyzer. The specimens were divided into three groups based on surface treatments including heat treatment subsequent to mirror polishing, grinding, and sandblasting. Specimens in each group were autoclaved at 134°C for 1, 3, 5, 10, and 15 h. The phases of the specimens were analyzed using an X-ray diffractometer, and the relative amount of the monoclinic phase was calculated and analyzed using Student's t-test and Newman-Keuls multiple comparisons test. Single routine autoclave treatment for sterilization did not promote the phase transformation in zirconia. The phase transformations of all specimens by autoclaving were correlated with grain size, except for the zirconia-alumina composite. Grinding or sandblasting treatments gave rise to increased formation of the monoclinic phase, especially for the zirconia-alumina composite, which showed the highest fraction for the monoclinic phase. The effects of surface treatments on the aging susceptibilities by autoclaving were different in the experimental groups. It is notable that not all zirconia ceramics show similar phase transformation by autoclaving after surface treatments.