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This ex vivo study aimed to evaluate the cleaning and shaping ability of a unique stainless steel rotary system (Gentlefile; MedicNRG, Kibbutz Afikim, Israel) compared with 2 nickel-titanium rotary instruments.Thirty human mandibular premolars with a 15° to 25° curvature were equally distributed into 3 groups for final instrumentation with Gentlefile Red (#23/0.04), HyFlex EDM OneFile (#25/0.08˜; Coltene/Whaledent, Altstätten, Switzerland), and ProTaper Next X2 (#25/0.06v; Dentsply Sirona, Ballaigues, Switzerland) (n = 10/each). The untouched canal area, volume changes, and transportation were evaluated on pre- and post-instrumentation micro–computed tomographic images. Five random regions of the canal wall located 1–7 mm from the apical foramen were evaluated with scanning electron microscopy for superficial debris and a smear layer via a 5-point scoring system. Data were compared using the Kruskal-Wallis test with post hoc Dunn's pairwise comparison test with Bonferroni correction and Wilcoxon signed-rank test (α = 5%).All instruments generated no overt procedural errors. Untouched area and volume changes did not show any significant differences among the 3 groups (P > .05). The Gentlefile exhibited less transportation at the level of 5–7 mm from the apex compared with ProTaper Next (P < .05). The Gentlefile showed a smaller debris score than ProTaper Next and better smear layer removal than the others (P < .05). Complete cleanliness was not achieved by any of the systems investigated.Canals instrumented with the Gentlefile exhibited less transportation at the mid-root level and better cleanliness than those instrumented with HyFlex EDM and ProTaper Next.