¹Associate Professor, University of Oslo, Norway

Abstract

Objective To assess the influence of alloy composition on the survival of amalgam restorations.

Study selection Data from 14 independent controlled clinical trials on the oral behaviour of Classes I and 2 amalgam restorations, with a follow-up between five and 15 years.

Data extraction and synthesis All data from the 14 trials were cumulated and re-evaluated by secondary analysis. For the analysis, 3119 restorations were available, which were made from 24 different alloys by a group of seven operators. The alloys were divided into four groups according to their zinc content (zinc-containing and zinc-free) and their copper content (conventional and high-copper). 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 restoration-related failures, survival functions of the restorations were estimated by alloy and alloy group.

Results The total number of failed restorations 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% survived. Zinc and a high copper content had an equally favourable influence on the survival rate, which was 70% after 13 years when either was present. The highest survival rates were of restorations of zinc-containing high-copper alloys: 85% after 13 years.

Conclusions This analysis suggests that the zinc and copper contents of the alloy influences survival of amalgam restorations.