Survival predictions of amalgam restorations

The purpose of this study was to evaluate survival predictions made for four different amalgam alloy restorations, using a mixture model involving the standard Weibull function. The amalgam alloys were placed by students and staff in patients attending a dental hospital, and 1680 restorations were examined over periods of up to 18 years. Based on maximum likelihood estimations of the parameters of the mixture model distribution, predictive survival distributions were generated and found to match closely the actuarial survival estimates established from the same data. The 13-year restoration survivals of one low-copper alloy could be predicted accurately from the 6-year survival results. However, another low-copper alloy and two high-copper alloys with much lower restoration failure rates required 18 years of data for accurate long-term survival predictions.