LONG-TERM SURVIVAL OF EXTENSIVE AMALGAM RESTORATIONS

In cost-effectiveness analysis and contemporary treatment planning str ategies, the postponement of placement of cast crowns plays an importa nt role. Extensive amalgam restorations that involve the rebuilding of cusps and the provision of auxiliary retention are thought to make th is postponement possible. This study reports the long-term survival (1 00 months) of extensive amalgam restorations in a randomized, controll ed clinical trial. The operational hypothesis was that the type of ret ention and the operator have a long-term influence on the survival and clinical functioning of extensive amalgam restorations. Three hundred extensive amalgam restorations were placed by three operators in mola r teeth in which one or more cusps were reconstructed. Five different auxiliary retention methods were used for retention of these restorati ons. Since the purpose of extensive amalgam restorations is considered to be two-fold (to restore a broken-down molar to function acceptably as an independent restoration and to create a substructure for subseq uent crown construction), survival was assessed at different levels. T he survival rate of extensive amalgam restorations as an independent r estoration was 88 +/- 2%. The functional survival rate (as an independ ent restoration or as a substructure) was 92 +/- 2%. The influence of experimental variables ('retention method' and 'operator') and backgro und variables ('tooth type', 'extension of extensive amalgam restorati ons', and 'age of patient') on the survival was analyzed by Log Rank a nd Breslow tests. The analyses revealed that there were no statistical ly significant influences on the survival rates except for the variabl e 'age of patient' (p less than or equal to 0.05). Extensive amalgam r estorations were more prone to failure in the group of older patients than in the group of younger ones. It is concluded that the clinical s urvival of extensive amalgam restorations is independent from several clinical variables in the study.