Fracture resistance of defective amalgam restorations repaired with a resin-based composite material

Background: Repair is used to increase the longevity of defective restorations, such as large amalgams. The aim of this study was to investigate the fracture resistance and fracture modes of mesio-occlusodistal (MOD) amalgam molar restorations with extensive cuspal fracture repaired or replaced using a bulk-fill resin-based composite material.

Methods: Amalgam restorations were placed in 84 permanent extracted molars and randomly assigned (n = 14) to groups: (1) MOD amalgam, (2) composite repair of 1-cusp fracture and adjacent proximal box, (3) composite repair of 1-cusp fracture, (4) composite repair of 2-cusp fracture, (5) replacement of 1-cusp defect and existing MOD amalgam, (6) replacement of 2-cusp defect and MOD amalgam. Each molar was prepared to simulate the assigned fracture and either repaired or replaced. Specimens were aged and then loaded to fracture. Fracture resistance and fracture modes were recorded.

Results: The authors found significant differences (P < .001) between group 4 (1,652.3 N) and groups 5 (3,095.0 N), 1 (2,669.8 N), 6 (2,658.6 N), and 2 (2,442.9 N) as well as between group 3 (2,133.5 N) and group 5 (3,095.0 N). The results of the Fisher exact test showed differences among groups (P < .001), with group 5 having the highest number of nonrestorable fractures as well as higher fracture resistance on average.

Conclusions: Composite material is a viable option for the repair and replacement of cuspal defects, especially in the case of a 1-cusp fracture and 1-cusp fracture involving the adjacent proximal box.

Practical implications: Within the limitations of this study, the repair of cusp fractures in existing MOD amalgam-restored molars is an appropriate treatment option, although replacement of the defect and existing restoration with resin-based composite will withstand higher forces.