Prediction of amalgam restoration longevity

The purpose of the present study was to assess predictions of longevity for amalgam restorations using a fitted Weibull distribution against base estimates using actuarial methods. The 1345 restorations involved were from 100 members of the Royal Australian Air Force whose dental conditions had been monitored regularly over a minimum period of 10 years. Based on maximum likelihood estimates of the parameters of a Weibull distribution, Weibull curves could be determined and were found to be very close to actuarial survival curves established from the same data set. However, Weibull estimates based on survival experience of less than 5-6 years failed to predict long-term survival. Using the 6 year actuarial survival data, the predicted and observed survival curves disagreed by less than 10 per cent for every time period. Twenty-five per cent of restorations had failed for the 6 year data, compared to 22 per cent in these first 6 years for the full 17 year data set.