Methods: Thirty extracted premolar single root human adult teeth were selected and prepared by Race rotary files up to MAF#35. Then they were divided into two groups of 15 (A and B). Group A obturated with gutta-percha and AH26 sealer and group B with Resilon system by lateral condensation technique. After 4 weeks all canals were retreated by Race rotary files and using chloroform and master apical file increased to #40 file. Then teeth were split longitudinally and remaining materials on surface of canals were visualized with streomicroscope with 20 magnification and digital photographs captured microscope. The amount of residueal materials and time of retreatment were analyzed with Mmann-withney and Freidman tests.
Results: The highest residual material value was in Resilon group and the difference between two groups was significant (P=0.09).The time required for re treatment was not significant between two groups (P=0.381).
Conclusion: Orthograde retreatment of Resilon was less efficient than that of gutta- percah with more residual materials on surfaces of root canals.