Objective: To compare the effect of using resin composite base materials on fracture strength of endodontically treated premolar teeth restored with endocrown restorations.
Materials and Methods: A total of 60 sound maxillary first premolars with standardized MOD cavities with endodontic treatment were selected for this study, except for intact control. They were randomly divided into six groups (n=10); G1: sound premolars ( negative control); G2: unrestored teeth (positive control); G3: MOD cavities with endocrown restorations. G4: MOD cavities with nanohybrid composite base and endocrown ; G5: MOD cavities with sonicfill bulk fill composite base and endocrown ; G6: MOD cavities with bulk fill flowable composite base and endocrown. Vita Enamic hybrid ceramic was used to fabricate the overlay restorations. All samples were subjected to thermocycling between 5Cº to 55Cº in water bath for a total of 2000 cycle with 10 seconds dwell time. Then specimens were individually mounted on a computer-controlled material testing machine (Instron 3345) with a load cell of 5 kN and the maximum load to produce fracture in Newton (N) was recorded.
Statistical analysis: Analysis of variance (ANOVA) and Kolmogorov Smirnov and Shapiro-Wilk tests was performed .
Results: Fracture strength of restored teeth was increased compared to unrestored teeth. The fracture strength of G6 (bulk fill flowable) was significantly higher than the fracture strength of G5,G4,G3 and not significantly different from G1( intact teeth).
Conclusion: The use of resin composite base material significantly increased the fracture strength of endodontically treated premolars with endocrown restorations.