We previously reported (AADR Abst. No. 1754, 2001) fatigue limits and fracture characteristics for two high-palladium alloys, Spartan Plus (Pd–Cu–Ga) and Protocol (Pd–Ga) [both Williams/Ivoclar]. Because of the recent price volatility of palladium, there has been renewed interest in the Pd–Ag alloys. Purpose: The objective of this study was to obtain information about the fatigue limit and fracture characteristics of a representative Pd–Ag alloy (Super Star, 60Pd–28Sn–6In–5Sn, Jelenko). Methods: Cast test bars with gauge diameter of 3 mm and gauge length of 15 mm were subjected to simulated porcelain-firing heat treatment, and tested in the as-cast surface condition under uniaxial tension-compression stress at 10Hz and an R-ratio of –1. Two replicate specimens were tested for each stress amplitude. The stress at which fracture did not occur after 2 x 10⁶ cycles was designated as the fatigue limit. Results: The fatigue limit of the Super Star was ~ 0.15 of the 0.2% yield strength (YS) in tension (655 MPa), similar to the result previously found for heat-treated Protocol. Complex fracture surfaces were observed with the SEM, having characteristic striations from fatigue crack propagation. Other striations were associated with eutectic structures found in Super Star with the transmission electron microscope (AADR Abst. No. 132, 2001). Casting porosity and dendrites in the largely fine-grained microstructure were also present. Conclusions: The latter may be sites of fatigue fracture initiation, but their occurrence should be minimized in small castings with dimensions of single-unit restorations. Further research is recommended to evaluate the effect of casting size and loading mode on the fatigue behavior of palladium-based casting alloys. Supported by NIDCR Grant DE10147.

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