Effects of hydrothermal aging on the wear behavior, mechanical properties, and microstructure of a multilayered zirconia

This study investigated the effects of hydrothermal aging on the wear, surface roughness, mechanical properties, and crystalline composition of multilayered zirconia. Blocks (14 × 14 × 1.5 mm) fabricated from multilayered zirconia (IPS e.max ZirCAD Prime, Ivoclar Vivadent) were divided into non-aged and aged groups and subjected to cyclic loading (150 N, 4 Hz, 600,000 cycles) with a horizontal sliding. The following analyses were performed: wear volume, surface roughness, XRD, EDS, SEM, Vickers hardness, and fracture toughness. Wear measurements were analyzed using Student’s t-test. Surface roughness was analyzed using ANOVA On ranks and Dunn’s test. Hardness and fracture toughness were evaluated based on the overlap of confidence intervals. XRD, EDS, and SEM were qualitatively analyzed. Hydrothermal aging significantly increased the wear volume of the multilayered zirconia to 27.8 × 10⁵±10.3 × 10⁵µm³, but decreased the surface roughness in the worn area. Aging induced phase transformation only in the 3Y-TZP layer and transition zone. Hardness was increased in the 3Y-TZP region, and fracture toughness increased in the transition zone and 3Y-TZP layer after aging. Overall, hydrothermal aging did not adversely affect the evaluated mechanical properties, indicating that the material has low susceptibility to hydrothermal degradation, which may be favorable for clinical application. However, the observed phase transformation may contribute to reduced wear resistance. Additionally, the distinct responses of the individual layers of multilayered zirconia to hydrothermal aging should be considered during clinical decision-making.