To assess the clinical performance of restorative materials with respect to mechanical failure, the shape of the restoration, the strength and fatigue properties and the loading history are important. This study deals with the feasibility of a method to estimate the mechanical lifetime of dental restorations. The method takes into account that the mechanical lifetime is a stochastic quantity determined by shape, strength and fatigue properties and by the cyclic nature of the mastication forces. The general outline of the method is described and the necessary experimental data are discussed. Preliminary estimates of the lifetime of a composite and an amalgam restoration are made. The method is found to be feasible and the estimated lifetimes of the restoration are of the same order of magnitude as found clinically.