Fracture resistance of endodontically treated molars restored with resin composites

Introduction: To conserve tooth structure, adhesive composite restorations that can provide intracoronal reinforcement are advocated to restore endodontically treated teeth. Aim: The objective of the study was to compare the fracture resistance of endodontically treated molars restored with cuspal coverage restorations using different resin composites. Materials and Method: Ninety extracted, maxillary molar teeth were randomly divided into two control groups and four test groups (n=15 each). In seventy five teeth, class II MOD cavities with mesio-palatal cusp cappings followed by root canal therapy and post endodontic restorations were done. Restorative materials tested were: nanohybrid composite (Filtek Z250 XT), bulk fill composite (Tetric Evoceram), fiber reinforced (Ribbond) composite and indirect composite (SR Adoro). After finishing and polishing of the restorations, teeth were subjected to thermocycling and then to compressive loading in a universal testing machine. The mean load necessary to fracture the teeth were recorded in Newtons and stress distribution in these restored molars were tested by finite element analysis(FEA). The mode of failure was observed using stereomicroscope. Statistical analysis was done using SPSS/PC version 20.0 software and the results were analyzed by one way ANOVA and Tukey's post hoc test. Results: Post endodontic restorations using fiber reinforced composite and indirect composites exhibited fracture resistance similar to sound intact teeth (p>0.05). Significant difference in fracture resistance was observed for nanohybrid composite when compared with fiber reinforced and indirect composite groups(p<0.05). Most of the restorable (favourable) fractures were observed in the nanohybrid composite group followed by the indirect composite group. Unrestorable fractures were seen mostly in the bulk fill composite group followed by the fiber reinforced composite group. Conclusion: Restorations with fiber reinforced and indirect composites increased the fracture resistance of endodontically treated teeth. Resin composites with good bonding ability transmit and distribute functional stresses and hold the potential to reinforce the weakened tooth structure.