In this study the effect of time on the marginal fracture behaviour of amalgam was determined. Six alloys in clinical service for up to 6 years were used as a data base and occlusal photographs were categorized according to a standard set of photographs depicting varying degrees of marginal fracture. The standard set of photographs was assigned a linear numerical scale, and the index of extent of fracture was considered to be an arithmetic mean based on this linear scale. An observed patient effect and unequal sample sizes were considered in the determination of both the mean and variance. The results of applying these procedures to the data of this study showed that marginal fracture increased with time for all alloys; that the relative ranking of alloys did not change with time; and that, with certain limitations, early time evaluations can predict long‐term behaviour. Copyright © 1979, Wiley Blackwell. All rights reserved
