THE INFLUENCE OF THE AMALGAM ALLOY ON THE SURVIVAL OF AMALGAM RESTORATIONS - A SECONDARY ANALYSIS OF MULTIPLE CONTROLLED CLINICAL-TRIALS

Data from 14 independent controlled clinical trials on the oral behavi or of Classes 1 and 2 amalgam restorations, with a follow-up between f ive and 15 years, were re-evaluated by secondary analysis for the infl uence of alloy composition on the survival of amalgam restorations. Fo r the analysis, 3119 restorations were available, which were made from 24 different alloys by a group of seven operators. The alloys were di vided into four groups according to their zinc content (zinc-containin g and zinc-free) and their copper content (conventional and high-coppe r). During the follow-up of the trials, the restorations were annually assessed for failures, which were classified as to (1) restoration-, (2) restorative process-, and (3) patient-related reasons. With the re storation-related failures, survival functions of the restorations wer e estimated by alloy and alloy group. The total number of failed resto rations was 481, of which 77% were restoration-related and 14% process -related. Eighty percent of the restoration-related failures were due to some form of fracture of the amalgam. Restorations of conventional zinc-free alloys had the shortest survival. After 13 years, only 25% s urvived. Zinc and a high copper content had an equally favorable influ ence on the survival rate, which was 70% after 13 years when either wa s present. The highest survival rates were of restorations of zinc-con taining high-copper alloys: 85% after 13 years. The zinc and copper co ntents of the alloy contributed to the corrosion resistance of the ama lgams, which in turn influenced the survival of the restoration. The c urrent ISO Standard 1559 on alloys for dental amalgam should be modifi ed to account for these factors that influence the survival of amalgam restorations.