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The aim of this study was to compare the remaining root canal obturation, volume of dentin removed, and apical transportation after retreatment of severely curved root canals by using Reciproc (REC) or ProTaper NEXT (PTN) systems.Twenty-eight mesial canals of mandibular molars were instrumented and then obturated with gutta-percha and sealer and allocated into 2 balanced groups (n = 14), the REC group (R25 file) and the PTN group (X3 and X2 files). Micro–computed tomography analysis was performed to assess the percentage of residual obturation material, the amount of dentin removed, and apical transportation. The effective time for the removal of obturation and procedural errors were recorded.Obturation was effectively removed from the root canal in the REC and PTN groups (P ≤ .001), and the percentages of remaining obturation material were similar between both groups (84.8% PTN vs 86.5% REC) (P > .05). The amount of dentin removed (3.17 ± 2.64 mm3 PTN versus 3.50 ± 2.82 mm3 REC), apical transportation (at 1 mm: 0.096 ± 0.189 mm PTN versus 0.093 ± 0.186 mm REC; at 3 mm: 0.059 ± 0.069 mm PTN versus 0.082 ± 0.080 mm REC; at 5 mm: 0.097 ± 0.093 mm PTN versus 0.133 ± 0.138 mm REC), and the working time (269.69 ± 19.25 seconds PTN versus 268.62 ± 16.37 seconds REC) were also similar in both groups (P > .05). One file fractured in the REC group.Both systems were equally effective in the removal of obturation from severely curved canals and can be used for retreatment. Neither system could completely remove the obturation material; therefore, additional techniques are needed to improve cleaning of the root canal.This study evaluates the behavior of ProTaper NEXT files in removing obturation material.Micro-CT images were also used to determine dentin removed and apical transportation.Neither ProTaper NEXT nor Reciproc systems completely removed the obturation material.