Failure modes of two Implant-supported oxide-ceramic Fixed-Partial-Denture Systems

Objectives: To compare fatigue and damage-modes between aluminum-oxide and zirconium-oxide all-ceramic systems in implant-supported fixed-partial-dentures (FPDs) using off-axis mouth-motion fatigue loading. Methods: Zirconium-oxide abutments* (n=36/group) were fabricated on NobelReplace* implant-replicas. Aluminum-oxide and zirconium-oxide bridge frameworks* (n=18/group) were CAD/CAM manufactured. Frameworks were veneered with hand-built up porcelains (*NobelBiocare). Abutments were screw-retained with 32N/cm torque and FPDs were cemented and incubated in water at 37°C for at least 14-days. Material-specific step-stress-profiles were designed based on load-to-failure values (n=2/group). Accelerated life testing was performed with distributed load immersed in water. Failure was defined by chipping or framework failure. Specimens were sectioned and inspected (polarized-specular-reflection-light-microscopy) at regular intervals to visualize crack propagation and failure mode. Reliability was compared using cumulative-damage step-stress analysis (Alta-7-Pro, Reliasoft). Results: Crack propagation was observed in the veneering porcelain during fatigue for both systems. The majority of zirconium-oxide FPDs demonstrated porcelain chipping as dominant failure mode. Nevertheless, fatigue of the zirconium-oxide frameworks was observed. Aluminum-oxide FPDs showed more dramatic failure, but were less limited by early porcelain chipping. Weibull-stress-level-probability-curves were calculated and the reliability (2-sided at 90.0% confidence bounds) for 50K cycles and a 400N load indicated values of 0.97(0.99/0.77) for zirconium-oxide FPDs and 0.82(0.92/0.60) for aluminum-oxide FPDs. Conclusions: Within the limitations of this study, mechanical-fatigue-test results demonstrated similar reliability for implant-supported aluminum-oxide and zirconium-oxide all-ceramic three-unit-FPDs under average clinical loads. A variation of failure modes is expected. Supported by Nobel Biocare, Goteborg, Sweden.