Fibre-reinforced composite crowns luted to implant abutments via electroformed primary copings: an in vitro retention study.

Aim: The aim of this study was to investigate the retention values and mode of failure of metal crowns and fibre-reinforced composite crowns. Methods: Seventy-five implants and the corresponding abutments were used. After the galvanic copings were fabricated, the specimens were distributed into three groups: in group A traditional metal crowns were realized, whereas in groups B and C fibre-reinforced composite crowns were made. In group B the same resin based cement used in group A was employed for luting the fibre-reinforced composite crowns to the galvanic copings, while in group C a dedicated self-adhesive composite cement was used. All galvanic coping/crown assemblies were cemented onto abutments with Panavia 21 cement. Specimens were subjected to a pull-out test; median retentive values and standard deviations were calculated. Results: All samples in the group A showed separation at the abutment-galvanic cap interface. All samples in the group B showed decementation at galvanic cap-crown interface. In 13 samples of the group C the decementation occurred at the abutment-galvanic cap interface and in 12 samples of this group the decementation occurred at the galvanic cap-crown interface. The mean retention value was 659.1 N±162.9 for group A, 304.7 N±101.4 for B and 635.4 N±155.9 for C. Differences between groups A/B and B/C are statistically significant (t-student test, P<0.01), while is not statistically different between groups A/C. Conclusion: When a self-adhesive composite cement is used, fibre-reinforced composite single crowns and conventional metal crowns show similar retentive performance.