Influence of low-temperature degradation on the wear characteristics of zirconia against polymer-infiltrated ceramic-network material

Statement of problem: Low-temperature degradation may affect zirconia restorations during their clinical service. Concerns have been raised about the effect of low-temperature degradation on the wear behavior of zirconia. Moreover, the wear resistance of this novel polymer-infiltrated ceramic-network material needs to be better evaluated. Purpose: The purpose of this in vitro study was to investigate the influence of aging on the wear resistance of zirconia opposing polymer-infiltrated ceramic-network material. Material and methods: Twelve specimens for 2 newly developed polymer-based materials (a polymer-infiltrated ceramic-network material VITA ENAMIC and a resin nanocomposite material Lava Ultimate), 2 commonly used glass-ceramic materials (IPS e.max CAD and VITABLOCS Mark II), and 2 conventional composite resin materials (VITA CAD-Temp and PMMA Disk) were tested; human enamel was used as a control group. The wear simulator used was a ball-on-disk type with zirconia balls, with and without autoclaving (134°C, 200 kPa, 20 hours) as antagonists. The vertical loss and volume loss of specimens and the roughness average of zirconia antagonists were measured with a 3-dimensional optical profilometer. Vickers hardness values were determined using a micro-Vickers hardness tester. Data were statistically analyzed with a mixed-model ANOVA for wear loss (vertical loss [μm] and volume loss [mm³]) and roughness average (μm) of zirconia antagonists and with the Kruskal-Wallis test for Vickers hardness values (α=.05). The Spearman correlation coefficient was used to determine the relationship between wear loss and hardness. Results: Results showed that specimens opposing the non-aged zirconia balls demonstrated significantly higher wear than those opposing the aged ones (P<.001). The polymer-infiltrated ceramic-network material VITA ENAMIC group (vertical loss=27.44-33.53 μm, volume loss=0.0198-0.315 mm³) and the resin nanocomposite material Lava Ultimate group (vertical loss=24.42-27.83 μm, volume loss=0.0159-0.0233 mm³) showed lower vertical loss and volume loss than the conventional composite resin groups (vertical loss=43.95-61.87 μm, volume loss=0.0395-0.0593 mm³) but higher wear than the glass-ceramic groups (IPS e.max CAD and VITABLOCS Mark II; vertical loss=8.95-11.47 μm, volume loss=0.0072-0.0094 mm³) and human enamel (vertical loss=9.95-12.32 μm; volume loss=0.0089-0.0103 mm³). The aged zirconia antagonists indicated greater roughness average values than the aged zirconia balls after the wear test (P<.001). Distinct abrasion-induced tracks were observed on the contact surfaces of the aged zirconia antagonists. Conclusions: Even though zirconia ceramic subjected to low-temperature degradation exhibited increased roughness after the wear test, it was still nonabrasive toward opposing materials. The polymer-infiltrated ceramic-network material showed intermediate wear resistance compared with glass-ceramic and conventional composite resin.