Influence of low-temperature degradation and wear cycles on the wear resistance of zirconia

Abstract

Objective The purpose of this study is to evaluate the influence of low temperature degradation on the wear behavior of zirconia. Methods Zirconia balls with and without autoclaving (134℃, 100 h) were used as the antagonist material in this study. Eight specimens of human enamel for each group were tested. For each enamel sample, a zirconia ball was used as the antagonist (n= 8) . The specimens and antagonist balls were subjected to a wear simulator (10 000, 20 000 and 50 000 loading cycles, 1.2 Hz, 49 N) and then the vertical loss and volume loss were measured by a three-dimensional (3D) optical profilometer. Roughness of zirconia balls was measured by the 3D optical profilometer as well. Hardness of the samples was determined using a micro-Vickers hardness tester. The software of SPSS 20.0 was used for statistical analysis. Two-Way ANOVA was performed to analyze the data of vertical loss (μm) and volume loss (mm3 × 10-3) for enamel samples and roughness (μm) of the zirconia balls and data of Vickers hardness were analyzed using One-Way ANOVA. Multiple pair-wise comparison of means was performed with Tukey′s Honestly Significant Difference (HSD) post hoc test (α= 0.05) . Results Results showed that human enamel samples opposing the non-aged zirconia balls demonstrated significantly less vertical loss (F20 000= 4.573, P20 000= 0.0364; F50 000= 49.385, P50 000<0.001) and volume loss (F20 000= 5.769, P20 000= 0.0210; F50 000= 61.792, P50 000<0.001) than those against the aged zirconia balls after 20 000 and 50 000 wear test cycles. No significant differences were observed after 10 000 wear test cycles for vertical loss (1.43 ± 0.07, 1.46 ± 0.12) and volume loss (2.36 ± 0.45, 2.31 ± 0.34; Fvertical loss= 0.721, Pvertical loss= 0.610; Fvolume loss= 0.0552, Pvolume loss= 0.801) . No significant differences were found for the roughness among the aged (0.0402 ± 0.0055, 0.0366 ± 0.0061) and non-aged zirconia balls (0.0402 ± 0.0055, 0.0366 ± 0.0061) after 10 000 and 20 000 were test cycles (F10 000= 0.0314, P10 000= 0.873; F20 000= 0.693, P20 000= 0.416) . However, after 50 000 chewing cycles aged zirconia balls (0.0596 ± 0.0045) showed significantly greater roughness than the non-aged ones (0.0386 ± 0.0027; F50 000= 128.793, P<0.001) . Vickers hardness for the aged zirconia balls 1257.0 ± 54.5 (HV1) was significantly lower than for the non-aged group 1385.8 ± 28.7 (HV1, F= 124.789, P<0.001) . Conclusions Low temperature degradation results in significant decrease in Vickers hardness for zirconia balls. Aged zirconia balls demonstrate less wear resistance after 20 000 and 50 000 chewing cycles compared to the non-aged zirconia ones. Key words: Zirconium oxide; Low temperature degradation; Wear cycle; Wear resistance