RESUMO
INTRODUCTION: The aim of the present study was to determine the disinfection of preparations carried out by using the Protaper or MTwo system in canals infected with Enterococcus faecalis. METHODS: Twenty-eight distobuccal canals of upper molars were used, in which the canals were sterilized after being enlarged to #20 file and then contaminated with an inoculation of a culture of E. faecalis. After the incubation period, bacterial samples were collected and were seeded on plates for analysis of colony-forming units (CFU)/mL. The teeth were divided into 2 groups according to the rotary system used for instrumentation; 2 noninstrumented teeth served as the control group. Then bacterial samples were collected and were seeded on plates for analysis of CFU/mL again. The data obtained were evaluated by the Wilcoxon and Mann-Whitney U tests. RESULTS: Bacterial reduction was 81.94% and 84.29%, respectively, in ProTaper and Mtwo systems, and there was no statistically significant difference (P > .05). CONCLUSIONS: Both systems, ProTaper and Mtwo, reduced the amount of bacteria in the mechanical disinfection of the root canal system, demonstrating that they are suitable for this purpose.