Reliability and fatigue failure modes of implant-supported aluminum-oxide fixed dental prostheses

Objectives: To investigate failure modes and reliability of implant-supported aluminum-oxide three-unit fixed dental prostheses (FDPs) using two different veneering porcelains. Material and methods: Thirty-six aluminum-oxide FDP frameworks were computer-aided designed and computer-aided manufactured and either hand-veneered(n = 18) or over-pressed(n = 18). All FDPs were adhesively luted to custom-made zirconium-oxide-abutments attached to dental implant fixtures (regular platform 4 × 13 mm). Specimens were stored in water before mechanical testing. A step-stress accelerated life test (SSALT) with three load/cycles varying profiles was developed based on initial single-load-to-failure testing. Failure was defined by veneer chipping or chipping in combination with framework fracture. SSALT was performed on each FDP inclined 30° with respect to the applied load direction. For all specimens, failure modes were analyzed using polarized reflected light microscopy and scanning electron microscopy. Reliability was computed using Weibull analysis software (Reliasoft). Results: The dominant failure mode for the over-pressed FDPs was buccal chipping of the porcelain in the loading area of the pontic, while hand-veneered specimens failed mainly by combined failure modes in the veneering porcelain, framework, and abutments. Chipping of the porcelain occurred earlier in the over-pressed specimens (350 N/85 k, load/cycles) than in the hand-veneered ones (600 N/110 k) (profile I). Given a mission at 300 N load and 100 or 200 k cycles, the computed Weibull reliability (two-sided at 90% confidence bounds) was 0.99(1/0.98) and 0.99(1/0.98) for hand-veneered FDPs and 0.45(0.76/0.10) and 0.05(0.63/0) for over-pressed FDPs, respectively. Conclusions: In the range of average clinical loads (300-700 N), hand-veneered aluminum-oxide FDPs showed significantly less failure by chipping of the veneer than the over-pressed. Hand-veneered FDPs under fatigue loading failed at loads ≥600 N.