الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The purpose of this study was to compare the efficacy of three rotary NiTi systems; Protaper retreatment system, K3 endo rotary files, Twisted rotary files and Hedstrom hand files in the removal of gutta-percha filling material from root canals with moderate and severe curvatures.
Methodology: Eighty curved root canals of human extracted mandibular molars were 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: ProTaper retreatment system, K3 rotary files, Twisted rotary files and Hedstrom hand files. Areas of remaining filling were traced, measured in mm2 using cone beam volumetric tomography (CBVT). Data were statistically analysed and level of significance was set at P ≤ 0.05.
Results: No statistically significant difference was observed between the amount of remaining filling in moderately and severely curved canals. At the apical third of the canals; the amount of remaining filling material was significantly lower using H-files and K3 rotary files. No significant difference was revealed between retreatment techniques at the middle, coronal thirds of the canals.
Conclusions: None of the experimental techniques guaranteed complete removal of the filling material from the root canal system. Hedstrom hand files and K3 rotary system proved to be more efficient than Protaper retreatment files and Twisted files in the removal of filling material from curved root canal walls. The apical part remains a challenge during retreatment procedure.