The purpose of this study was to compare the efficacy of three rotary NiTisystems; Protaper retreatment system, K3 endo rotary files, Twisted rotary files andHedstrom hand files in the removal of gutta-percha filling material from root canalswith moderate and severe curvatures.Methodology: Eighty curved root canals of human extracted mandibular molarswere selected. According to canal curvature, specimens were divided into ; (Group I)Moderately curved canals (25-350), (Group II) Severely curved canals (35-450).Canals were instrumented and filled with laterally condensed gutta-percha and sealer.Removal of gutta-percha was performed with the following techniques: ProTaperretreatment system, K3 rotary files, Twisted rotary files and Hedstrom hand files.Areas of remaining filling were traced, measured in mm2 using cone beam volumetrictomography (CBVT). Data were statistically analysed and level of significance wasset at P ≤ 0.05.Results: No statistically significant difference was observed between the amount ofremaining filling in moderately and severely curved canals. At the apical third of thecanals; the amount of remaining filling material was significantly lower using H-filesand K3 rotary files. No significant difference was revealed between retreatmenttechniques at the middle, coronal thirds of the canals.Conclusions: None of the experimental techniques guaranteed complete removal ofthe filling material from the root canal system. Hedstrom hand files and K3 rotarysystem proved to be more efficient than Protaper retreatment files and Twisted files inthe removal of filling material from curved root canal walls. The apical part remains achallenge during retreatment procedure.