Background: There were no comparing data about the effect of recently developed file system OneCurve on apical debris extrusion. Aim: The aim of this in vitro study was to compare the influence of the rotary nickel-titanium (Ni-Ti) files on apical debris extrusion after cervical preflaring. Materials and Methods: Sixty-six lower incisor teeth with a single root canal were used in this study. After the determination of working length, the specimens were divided into six experimental groups according to root canal preparation. G1: ProTaper-Next, G2: EndoFlare + ProTaper-Next, G3: 2Shape, G4: EndoFlare + 2Shape, G5: OneCurve, and G6: EndoFlare + OneCurve. Each specimen was inserted into separate preweighed Eppendorf tubes to collect apically extruded debris. A total of 8 mL of distilled water was used for each specimen for irrigation. After the completion of root canal preparation, the Eppendorf tubes were weighed again after evaporation to calculate the amount of extruded debris. The data were statistically analyzed with one-way analysis of variance (P > 0.05). Results: There was no statistically significant difference between the experimental groups. The amount of apically extruded debris was similar after preparing root canals with ProTaper-Next, 2Shape, and OneCurve with and without cervical preflaring. Conclusion: Under the conditions of this in vitro study, ProTaper-Next, 2Shape, and OneCurve files had similar apical debris extrusion values. Cervical preflaring of root canals did not affect the amount of apically extruded debris.