Effects of aging on tensile fatigue strength of bovine dentin

The effects of aging on the tensile fatigue strength of bovine dentin were investigated. Tensile tests and tensile fatigue tests were performed in 37 degrees C water with bovine dentin specimens of two different age groups. The tensile strengths of the young group and the adult group were 74.0 MPa and 72.7 MPa, respectively; there was no significant difference between the young and the adult group. However, the tensile fatigue strength of the adult group, 46.9 MPa, was significantly weaker than that of the young group, 51.0 MPa. There was a obvious difference between the tensile fracture surface and the tensile fatigue fracture surface; a smooth surface of the peritubular dentin and an uneven surface of the intertubular dentin were clearly distinct in the fatigue fracture surface. Plugged dentinal tubules and narrower dentin tubules were commonly observed in the adult group. These morphological changes were suggested to be the reason for the decrease in the tensile fatigue strength with aging.