Aim: To evaluate the ex vivo effectiveness of four different rotary systems in removing filling material from curved root canals, and to determine the time required to do so. Materials and methods: Forty-eight curved mesiobuccal root canals of first and second mandibular molars were prepared, obturated, and randomly divided into four groups (n = 12), according to the retreatment rotary system used for filling material removal, as follows: R-Endo, Mtwo Retreatment, D-RaCe, and ProTaper. The amount of remaining filling material was assessed in buccolingual and mesiodistal radiographs using Image Tool 3.0 software. The Kruskal-Wallis test was used to compare differences between the groups. The time required for filling material removal was recorded using a digital stopwatch. Results: There was no statistically significant difference between the groups with regard to the amount of remaining filling material (P > 0.05). Filling material removal using Mtwo files (mean 3.30 min) was significantly faster than using the ProTaper (5.47 min), D-RaCe (4.69 min) and R -Endo (4.48 min) systems (P 0.05). Conclusion: All retreatment rotary systems produced similarly clean canals, but the Mtwo Retreatment system was faster. Palabras clave: gutta-percha, NiTi instruments, retreatment, root canal preparation