Objective: The aim of this study was to compare the fracture resistance of roots obturated with different materials. Study design: Sixty root canals were instrumented and divided into 4 equal groups (n = 15 each). The root canals in group 1 were filled with AH26 sealer and gutta-percha, in group 2 with Resilon and Epiphany, and in group 3 with Ketac-Endo Aplicap and gutta-percha. Fifteen root canals had no obturation. The force required to fracture was recorded. The data was analyzed with analysis of variance and Duncan test. Results: The mean force of fracture for group 1 was significantly higher than for the other 3 groups (P < .05). There was significant difference between group 2 and group 3 (P < .05). Group 2 and group 3 were not significantly different from the control group (P > .05). Conclusion: The use of AH26 + gutta-percha increased the fracture resistance of instrumented root canals compared with Resilon + Epiphany and Ketac-Endo Aplicap + gutta-percha. © 2007 Mosby, Inc. All rights reserved.