The effect of aging on the wear performance of monolithic zirconia

Investigate the effect of aging on the wear behavior of glazed vs polished monolithic zirconia and to establish if glazing provides protection against low temperature degradation.

40 1-mm-diameter spheres made from four differently treated monolithic zirconia (VITA YZ® HT); polished, polished-aged, glazed and glazed-aged (n = 10), were tested in a wear testing machine (UFW200) against bovine enamel in artificial saliva as per the following settings (ISO20808:2016): ball-on-disc configuration, 5 N vertical load, 0.1 m/s sliding speed, 400 m sliding distance and 37 °C temperature. Vertical substance loss (mm) wear of zirconia and enamel specimens was measured. Data were statistically analyzed with Kruskal-Wallis one-way ANOVA test (α > 0.05).

Glazed-aged zirconia specimens resulted in the greatest amount of enamel wear (0.823 mm ± 0.157) followed by glazed (0.729 mm ± 0.289), polished-aged (0.377 mm ± 0.201) then polished (0.247 mm ± 0.125). In the groups with the same surface finish, aging showed no statistical difference in wear (P > 0.008). Glazing resulted in a higher enamel wear compared with polishing that was statistically significant (P < 0.008) except when the polished specimens were aged and the glazed specimens were not aged.

Aging increases abrasiveness of monolithic zirconia regardless of the type of surface finish. The effect of aging is "latent" and only revealed under mechanical loading during wear simulation which increases surface roughness and wear by adversely affecting zirconia's mechanical properties, making it less capable to maintain its initial surface smoothness. The glaze layer may protect zirconia from LTD, however, it is susceptible to aging which further increases its abrasiveness.