How oral environment simulation affects ceramic failure behavior

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Abstract

Statement of problem.

Investigating the mechanical behavior of ceramics in a clinically simulated scenario contributes to the development of new and tougher materials, improving the clinical performance of restorations. The optimal in vitro environment for testing is unclear.

Purpose.

The purpose of this in vitro study was to investigate the failure behavior of a leucite-reinforced glass-ceramic under compression loading and fatigue in different simulated oral environment conditions.

Material and methods.

Fifty-three plate-shaped ceramic specimens were produced from computer-aided design and computer-aided manufactured (CAD-CAM) blocks and adhesively cemented onto a dentin analog substrate. For the monotonic test (n=23), a gradual compressive load (0.5 mm/min) was applied to the center of the specimens, immersed in 37°C water, using a universal testing machine. The initial crack was detected with an acoustic system. The fatigue test was performed in a mechanical cycling machine (37°C water, 2 Hz) using the boundary technique (n=30). Two lifetimes were evaluated (1×106 and 2×106 cycles). Failure analysis was performed using transillumination. Weibull distribution was used to evaluate compressive load data. A cumulative damage model with an inverse power law (IPL) lifetime-stress relationship was used to fit the fatigue data.

Results.

A characteristic failure load of 1615 N and a Weibull modulus of 5 were obtained with the monotonic test. The estimated probability of failure (Pf) for 1×106 cycles at 100 N was 31%, at 150 N it was 55%, and at 200 N it was 75%. For 2×106 cycles, the Pf increased approximately 20% in comparison with the values predicted for 1×106 cycles, which was not significant. The most frequent failure mode was a radial crack from the intaglio surface. For fatigue, combined failure modes were also found (radial crack combined with cone crack or chipping).

Conclusions.

Fatigue affects the fracture load and failure mode of leucite-reinforced glass-ceramic.

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