Marginal Fracture of Amalgam Restorations

Marginal fracture characteristics of clinical restorations made from three amalgam alloys were evaluated during a four-year period. Marginal fracture increased with age; the rate of increase was different among alloys, and the ranking of alloys remained the same during the four years. In a previous studyJ the marginal fracture characteristics of amalgam restorations made from three commercial alloys were compared. The results of the study indicated a differ-ence among alloys after one year of clinical service. Several questions were raised in re-lation to these results. First, would marginal fracture become more extensive with years of clinical service? Second, if this were true, would the rate of increase of marginal frac-ture differ among alloys? Third, would the relative order of extent of marginal fracture among alloys remain the same with years of service? Because the restorations in this pre-vious study1 have been in service for four years, sufficient data are available to answer these questions. Answers to these questions would make it possible to establish the proper design of clinical investigations so that the integrity and longevity of amalgam restorations could be evaluated in a valid manner. Decisions need to be made such as the length of time a clinical study should be conducted and whether the results of a one- or two-year study can be extrapolated to predict five-or ten-year results. In view of the recently suggested changes in amalgam systems,23 properly designed clinical studies are es-sential to validate claims for improvement