Improving fatigue resistance of translucent 4Y-PSZ zirconia through glass gradation

To evaluate the effect of graded glass infiltration on the fatigue behavior and mechanical reliability of translucent 4Y-PSZ zirconia before and after hydrothermal aging, disc-shaped specimens were fabricated by uniaxial pressing and divided into control and glass-graded groups (n = 36/group). Glass infiltration was performed on pre-sintered specimens followed by final sintering, and half of the specimens from each group underwent hydrothermal aging (134°C, 2.2 bar, 20 h). Microstructure and phase composition were assessed by scanning electron microscopy and x-ray diffraction. Mechanical performance was evaluated using step-stress accelerated life testing, with Weibull statistics, reliability analysis, and inverse power-law modeling. Glass-graded specimens demonstrated higher reliability and characteristic strength (≈330 MPa increase) with similar Weibull modulus compared to controls. The inverse power-law parameter α₀ was higher for the glass-graded group, indicating extended fatigue life, whereas comparable α₁ values suggested similar life-stress relationships. Hydrothermal aging did not significantly affect mechanical performance, although phase transformation occurred in the control group. Fractography revealed surface-initiated failures in controls and interface-related crack initiation in glass-graded specimens. Graded glass infiltration improved the fatigue reliability and characteristic strength without compromising hydrothermal stability of 4Y-PSZ. These results suggest that glass-graded 4Y-PSZ may expand the clinical applicability of translucent zirconia for long-span (≥4-unit) prosthetic reconstructions.