Five-Year Clinical Performance of Complex Class II Resin Composite and Amalgam Restorations—A Retrospective Study

The aim of this retrospective study was to investigate the clinical performance of posterior complex resin composite (RC) and amalgam (AM) restorations after a five-year period. One hundred and nineteen complex Class II restorations placed by dental students were evaluated using the USPHS criteria. Data were analyzed using Chi-square, Mann–Whitney, and Wilcoxon tests at a 0.05 level of significance. After five years, the percentages of clinically satisfactory complex Class II RC and AM restorations were 78% and 76.8%, respectively. The main reasons for the failure of AM restorations included secondary caries (Bravo—10.1%), defective marginal adaptation (Charlie—8.7%), and fracture of the tooth (Bravo—7.2%). RC restorations presented failures related to the fracture of the restoration (Bravo—16%) and defective marginal adaptation (Charlie—8.2%). There was a significantly higher incidence of secondary caries for AM restorations (AM—10.1%; RC—0%; p = 0.0415) and a higher number of fractures for RC restorations (AM—4.3%; RC—16%; p = 0.05). Regarding anatomy, AM restorations presented a significantly higher number of Alfa scores (49.3%) compared to RC restorations (22.4%) (p = 0.0005). The results of the current study indicate that complex class II RC and AM restorations show a similar five year clinical performance.