Fracture resistance of endodontically treated molars restored with extensive composite resin restorations.

Statement of Problem: When cuspal coverage is required, there is no evidence that indirect composite resin restorations are superior to direct restorations in terms of biomechanical behavior.
Purpose: The purpose of this in vitro study was to compare the fracture resistance of cusp-replacing direct and indirect composite resin restorations in endodontically treated molars.
Material and Methods: Forty-five human mandibular molars were selected and divided into 3 groups (n=15): DIR specimens, restored with direct composite resin (Estelite Sigma) restorations; IND specimens, restored with indirect composite resin (Estelite Sigma) restorations, and control specimens, which remained intact. Endodontic treatment was performed using NiTi ProTaper rotary instruments, and teeth were filled using lateral condensation of gutta-percha and sealer. Extensive Class II MO cavities were prepared, and the 2 mesial cusps were reduced, allowing a 2-mm layer of composite resin. All teeth were prepared to the same dimensions, considering reasonable human variation. Specimens were loaded to failure and the fracture loads were recorded (N). The mode of fracture was determined using a stereomicroscope and classified as favorable or unfavorable failure. The data were subjected to a Kruskal-Wallis test, multiple-comparison Mann-Whitney test, and a chi-square test (alpha=.05).
Results: Significant differences (P<.001) were observed between the control group and both DIR and IND groups. However, no significant difference was found between the DIR and IND groups. The chi-square test did not show a significant difference in the frequencies of favorable/unfavorable failure modes among the 3 groups (P=.981).
Conclusions: No significant difference was observed in the fracture resistance of endodontically treated molars restored to original contours with an extensive cusp-replacing direct or indirect composite resin restoration.