Figure 10. The critical flaw size in dentin as a function of far-field applied stress (MPa). The critical flaw size is calculated for an elliptical flaw according to Eq. 25. The dashed line corresponds to the fracture toughness established by El Mowafy and Watts (1986): K_c = 3.08 MPa m. The solid line corresponds to the more conservative estimate of the fracture toughness determined by Imbeni et al. (2002): K_c = 1.8 MPa m. Knowledge of the critical flaw size is of great importance in lifetime modeling.