Effects of Aging on Mechanical and Optical Properties of Translucent and Opaque Zirconia

This study evaluated the effect of hydrothermal aging on opti-cal and mechanical properties of opaque and translucent zirconia.

For the biaxial flexural strength (BFS) test, 40 sintered opaque and translucent disc-shaped zirconia, and for the assessment of surface rough-ness and optical properties, 20 specimens were fabricated and artificially aged in an autoclave for 10 h. The CIE L*a*b* color parameters were measured. The translucency parameter (TP), contrast ratio (CR), opalescence (OP), and color difference against a white (ΔEW) and a black (ΔEB) background were all calculated. The surface roughness (Ra and Rz) was analyzed using a profilometer and the BFS test was performed at a crosshead speed of 1 mm/min. Data were analyzed using two-way ANOVA, t-test, and Mann-Whitney test (α=0.05).

The mean Ra (P=0.023) and Rz (P=0.011) significantly decreased after aging. Aging had no significant effect on TP (P=0.384), CR (P=0.261), or BFS (P=0.912). The mean TP values of translucent specimens were significantly higher than those of opaque specimens (P=0.046). For translucent specimens, the mean OP did not signifi-cantly change after aging (P=0.685) but aging significantly increased the OP of opaque specimens (P=0.007). The mean ΔEW and ΔEB of translucent specimens were higher than those of opaque specimens (P=0.044 and P=0.019, respectively).

Although aging affected the OP parameter, other optical properties and also BFS of both zirconia types were not affected by hydrothermal aging. However, the surface roughness of both zirconia types significantly decreased as a re-sult of aging.