A 4-year clinical evaluation of extensive amalgam restorations--description of the failures

The 4-year evaluation of a randomized controlled clinical trial to the functioning of Extensive Amalgam Restorations (EAR) is reported. In this trial 300 EAR were made by three operators on molar teeth. Five different auxiliary retention methods were used to retain these restorations. In the evaluation a differentiation in 'absolute' and 'relative' failures was made. After 4 years seven absolute failures (EAR dislodged or removed) were encountered (2%). When relative failures (endodontic treatment or restoration at margin) are also taken into account the number of failures increased to 31 (10%). Due to the low number of failures, no significant influences from experimental variables (c.q. retention method or operator) could be detected. It may be concluded that the results of this interim analysis of the clinical functioning of EAR are promising. It is thought that careful evaluation of cusp strength and reducing weak cusps diminishes clinical failure and as a result, it is not necessary to protect an EAR with a cast restoration in the first 4 years of its clinical life.