The Weibull distribution applied to post and core failure

In this study, data on initial failure loads of direct post and core-restored premolar teeth were analyzed using the Weibull distribution. Restorations consisted of a prefabricated titanium alloy post, and an amalgam, composite or glass cermet core buildup in human upper premolar teeth. The specimens were subjected to compressive forces until failure at angles of 10, 45 and 90 degrees to their long axis. The two- and three-parameter Weibull distributions were compared for applicability to the failure load data. For estimation of the parameters of the two-parameter distribution: sigma 0 (reference stress) and m (Weibull modulus), linear regression was used. In this distribution, it is assumed that the third parameter, sigma u (cut-off stress), equals 0. The Maximum Likelihood (MLH) method was used to estimate all three parameters. It was found that the choice of distribution has a strong influence on the estimated values and that the three-parameter distribution is best fitted for the failure loads in this study. Comparisons were made between the failure probability curves as found by MLH estimation for the different core materials and loading angles. The results indicated that the influence of loading angle on the failure mechanism was stronger than that of core material.