Figure 9. Ultimate tensile strength data from Lehman (1967) (open circles) and Staninec et al.2002 (solid circles). The data have been graphed in the form of a Weibull probability distribution function, with the abscissa given by the natural log of the failure stress, and the failure probability, P_f, given by Eq. 23. Both sets of data fit the Weibull distribution function (R² = 0.97), although the slopes, m, are different. The slope of the curve determines the sensitivity of the tensile strength to specimen size. Weibull behavior is an indication that a distribution of flaws determines the magnitude of the tensile strength of dentin.