Figure 2. Stress-life (S/N) data obtained for human dentin in HBSS at 37°C in the form of the stress-amplitude, _a, as a function of the number of cycles to failure, N_f. Results are shown (a) for various stress-ratios at a constant frequency (10 Hz), and (b) for various frequencies at constant stress-ratio (R = 0.1). Horizontal arrows represent samples that did not fail ("run-outs").