Step-stress analysis for predicting dental ceramic reliability

AbstractObjective t the hypothesis that step-stress analysis is effective to predict the reliability of an alumina-based dental ceramic (VITA In-Ceram AL blocks) subjected to a mechanical aging test. s aped ceramic specimens were fabricated, polished to 1 μm finish and divided into 3 groups (n = 10): (1) step-stress accelerating test; (2) flexural strength-control; (3) flexural strength-mechanical aging. Specimens from group 1 were tested in an electromagnetic actuator (MTS Evolution) using a three-point flexure fixture (frequency: 2 Hz; R = 0.1) in 37 °C water bath. Each specimen was subjected to an individual stress profile, and the number of cycles to failure was recorded. A cumulative damage model with an inverse power law lifetime-stress relation and Weibull lifetime distribution were used to fit the fatigue data. The data were used to predict the stress level and number of cycles for mechanical aging (group 3). Groups 2 and 3 were tested for three-point flexural strength (σ) in a universal testing machine with 1.0 MPa/s stress rate, in 37 °C water. Data were statistically analyzed using Mann–Whitney Rank Sum test. s tress data analysis showed that the profile most likely to weaken the specimens without causing fracture during aging (95% CI: 0–14% failures) was: 80 MPa stress amplitude and 105 cycles. The median σ values (MPa) for groups 2 (493 ± 54) and 3 (423 ± 103) were statistically different (p = 0.009). icance ing profile determined by step-stress analysis was effective to reduce alumina ceramic strength as predicted by the reliability estimate, confirming the study hypothesis.