Abstract: Abstract Objective  To evaluate the influence of different root canal filling systems on the fracture resistance of roots. Methods    68 single canal premolars were selected. The crowns were removed at the cementoenamel junction. And then they were randomly divided into four groups.The root canals of groupA, B and C were instrumented to F3 with rotary Protaper system using crown-down technique. Group A root canals were obturated with master gutta-percha cone and Cortisomol sealer by using cold lateral compaction.Group B root canals were obturated with gutta-percha and Cortisomol sealer by using warm vertical compaction. Group C root canals were obturated with RealSeal by using cold lateral compaction.Group D root canals were not instrumented or obturated. Then placed all the specimen in a universal testing machine and loaded each specimen to fracture. For each specimen，we recorded the force to fracture and the fracture mode of the teeth specimen using an optical stereomicroscope. Results  The force required to fracture the roots of Group D was significantly higher than that required to fracture the roots of all other groups. The force required to fracture the roots of Group C was significantly higher than that required to fracture the roots of Group A and B. In the Group A and B,the ruptures were mainly occurred in the dentine and sealer interface. In the Group C, there was a predominance of mixed failures．Conclusion   Teeth obturated with RealSeal were more resistant to fracture than those obturated with the other two systems.

Key words: Root canal obturation, tooth Root, resistance, RealSeal, vertical condensation, lateral condensation