Transition behavior in fatigue of human dentin: Structure and anisotropy

Abstract The influence of tubule orientation on the transition from fatigue to fatigue crack growth in human dentin was examined. Compact tension (CT) and rectangular beam specimens were prepared from the coronal dentin of molars with three unique tubule orientations (i.e., 0°, 45° and 90°). The CT specimens ( N =25) were used to characterize fatigue crack initiation and steady-state cyclic extension, whereas the rectangular beams ( N =132) were subjected to 4-pt flexure and used in quantifying the stress-life fatigue response. The transition behavior was analyzed using both the Kitagawa–Takahashi and El Haddad approaches. Results showed that both the fatigue crack growth and stress-life responses were dependent on the tubule orientation. The average Paris Law exponent for crack growth perpendicular (90°) to the tubules ( m =13.3±1.1) was significantly greater ( p