Background: The goal of nonsurgical retreatment is the removal of all filling materials to completely disinfect the whole root canal space. Recently Resilon obturating system has been introduced as a root canal filling material.

  Objective: To compare Gutta-percha and Resilon removal, using ProTaper rotary files with chloroform or heat in endodontic retreatment.

  Methods: This experimental study was performed on sixty-four human single-canal lower jaw extracted premolars at Dental School, Qazvin University of Medical Sciences during 2010. Following separating teeth crowns from the cementoenamel junction, canals were instrumented using step-back technique with k-files. Later, the extracted teeth were randomly divided into four groups of 16 teeth. Canals were obturated with either gutta-percha/AH26 (groups 1,2) or Resilon/Epiphany (groups 3,4). Retreatment for groups 1 and 3 was performed with ProTaper system and heat and for groups 2 and 4 with ProTaper system and chloroform using crown-down technique. Once the retreatment procedure was completed and justified, roots were sectioned longitudinally and examined under stereomicroscope. Data were analyzed using T-test, Kruskal-Wallis, and Mann-Whitney tests.

  Findings: In all groups, some filling materials (core material and sealer) were seen on the canal walls. Although, amount of Gutta-Percha/AH26 and Resilon/Epiphany system residue were similar, the amount of residual materials in group 4 was significantly more than other groups (P<0.05). Furthermore, the amount of residual materials in group 3 was more than group 1 in the coronal third of canals (P<0.05). The time required to remove filling material in group 2 was significantly higher than those of other groups (P<0.05).

  Conclusion: According to our findings, Resilon, like Gutta-percha, is re-treatable. However, none of these two materials could be completely removed from root canal walls.