BackgroundThe purpose of this study was to compare the efficacy of nickel-titanium rotary systems with or without the retreatment instruments in the removal of gutta-percha from the apical third.MethodsThe systems compared were as follows: ProTaper Universal (PT), ProTaper Universal Retreatment (PTr), Mtwo (M2) and Mtwo Retreatment (M2r). Sixty extracted mandibular incisors were treated with a crown-down technique and filled with gutta-percha and sealer. The apical diameter was standardized in 0.30 mm, 1 mm from the apex. The teeth were distributed into 4 experimental groups: PT, PTr, M2 and M2r. In PTr and M2r groups, filling materials were removed by PTr/M2r followed by root canals preparation up to a PT F4/M2 40; in groups PT/M2, the filling materials were removed and the root canals were prepared by PT up to a PT F4/M2 up to a M2 40. The roots were split and photomicrographing. The percentage of clean area in the apical 5 mm was calculated using software. Data were analyzed with the Kruskal-Wallis test.ResultsRemaining material was found in all hemisections and there was no statistically significant difference between the groups (p = 0.09). Considering the surface of the canal walls of all teeth, the mean of the percentage of clean area was 54%.ConclusionsConsidering the applied methodology, remaining filling material was found in all hemisections, regardless of the retreatment technique and PT or M2 were as effective as PTr/PT or M2r/M2.