On the in vitro fatigue behavior of human dentin: effect of mean stress.

Human dentin is susceptible to failure under repetitive cyclic-fatigue loading. This investigation seeks to address the paucity of data that reliably quantify this phenomenon. Specifically, the effect of alternating vs. mean stresses, characterized by the stress- or load-ratio R (ratio of minimum-to-maximum stress), was investigated for three R values (-1, 0.1, and 0.5). Dentin was observed to be prone to fatigue failure under cyclic stresses, with susceptibility varying, depending upon the stress level. The "stress-life" (S/N) data obtained are discussed in the context of constant-life diagrams for fatigue failure. The results provide the first fatigue data for human dentin under tension-compression loading and serve to map out safe and unsafe regimes for failure over a wide range of in vitro fatigue lives (< 10(3) to > 10(6) cycles).