Fracture toughness of human dentin.

Plane strain fracture toughness (KIC) was determined for coronal dentin using compact tension test-pieces obtained from recently extracted permanent lower molar teeth. Specimens were prepared and tested such that the moving crack front was aligned parallel to the tubule orientation. The fracture toughness (KIC) was temperature-invariant in the range 0-60 degrees C, and the mean value obtained was 3.08 MN.(m)-1.5 (SD: 0.33). The critical strain energy release rate (GIC) of dentin was also calculated utilizing modulus data and was found to increase slightly with temperature, possibly as a consequence of significant temperature-dependence of the modulus: GIC = 2.31 (T degree C) + 653.2 (J .m-2) The fracture toughness of dentin is midway in the range (0.23 - 6.56) observed for cortical bone and is a factor of two greater than that exhibited by most current restorative materials.