Contributions of stress corrosion and cyclic fatigue to subcritical crack growth in a dental glass-ceramic

AbstractObjective jective of this study was to test the following hypotheses: (1) both cyclic degradation and stress-corrosion mechanisms result in subcritical crack growth (SCG) in a fluorapatite glass-ceramic (IPS e.max ZirPress, Ivoclar-Vivadent) and (2) there is an interactive effect of stress corrosion and cyclic fatigue to accelerate subcritical crack growth. s gular beam specimens were fabricated using the lost-wax process. Two groups of specimens (N = 30/group) with polished (15 μm) or air-abraded surface were tested under rapid monotonic loading. Additional polished specimens were subjected to cyclic loading at two frequencies, 2 Hz (N = 44) and 10 Hz (N = 36), and at various stress amplitudes. All tests were performed using a fully articulated four-point flexure fixture in deionized water at 37 °C. The SCG parameters were determined using the ratio of inert strength Weibull modulus to lifetime Weibull modulus. A general log-linear model was fit to the fatigue lifetime data including time to failure, frequency, peak stress, and the product of frequency and logarithm of stress in ALTA PRO software. s rameters determined were n = 21.7 and A = 4.99 × 10−5 for 2 Hz, and n = 19.1 and A = 7.39 × 10−6 for 10 Hz. After fitting the general log-linear model to cyclic fatigue data, the coefficients of the frequency term (α1), the stress term (α2), and the interaction term (α3) had estimates and 95% confidence intervals of α1 = −3.16 (−15.1, 6.30), α2 = −21.2 (−34.9, −9.73), and α3 = 0.820 (−1.59, 4.02). Only α2 was significantly different from zero. icance clic fatigue does not have a significant effect on SCG in the fluorapatite glass-ceramic evaluated and (2) there was no interactive effect between cyclic degradation and stress corrosion for this material.