Fracture strength of amalgam crowns with repaired endodontic access

Endodontic therapy is accessed occlusally in posterior teeth, many of which have large, pre-existing amalgam restorations. These teeth are also commonly restored with an occlusal amalgam to repair the access opening. This study determined the fracture resistance of complex amalgam restorations that have repaired endodontic access compared with original, unrepaired, complex amalgams on endodontically-treated teeth. Two groups of 30 molars were used in the study. The first group was decoronated and received an endodontic access preparation. These teeth were restored using chamber retention and four TMS pins. The second group was decoronated and restored using pin retention. Later, they received an endodontic access through the restoration. The access was then repaired with amalgam. The samples were loaded in an Instron Universal Testing Machine until failure. The Group 1 samples failed at a mean force of 2297.5 N. The mean failure load for the samples in Group 2 was 1586.1 N. Student's t-test found this difference to be statistically significant. Endodontic access through an amalgam crown significantly compromises the fracture strength of the original restoration.