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

Statement of problems. 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 degrees 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 [mu m] and volume loss [mm(3)]) and roughness average (mu m) of zirconia antagonists and with the Kruskal-Wallis test for Vickers hardness values (alpha=.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 mu m, volume loss=0.0198-0315 mm(3)) and the resin nanocomposite material Lava Ultimate group (vertical loss=24.42-27.83 mu m, volume loss=0.0159-0.0233 mm(3)) showed lower vertical loss and volume loss than the conventional composite resin groups (vertical loss=43.95-61.87 mu m, volume loss=0.0395-0.0593 mm(3)) but higher wear than the glass-ceramic groups (IPS e.max CAD and VITABLOCS Mark II; vertical loss=8.95-11.47 mu m, volume loss=0.0072-0.0094 mm(3)) and human enamel (vertical loss=9.95-12.32 mu m; volume loss=0.0089-0.0103 mm(3)). 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.