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It was the aim of this study to investigate the incidence of file breakage and distortion when the ProTaper, K3 Endo, and ProFile systems were used to instrument canals in the severely curved roots of extracted molars.Forty-five roots of extracted mandibular and maxillary molars with curvatures between 40 and 75 degrees were chosen for this study. The canals in group 1 were instrumented with the ProFile system. Roots in group 2 were instrumented with the ProTaper system, and those in group 3 were instrumented with the K3 Endo system. The three systems were used according to the manufacturers' instructions.The proportion of files distorted was 15.3% for the ProFile group, 2.4% for the ProTaper group, and 8.3% for the K3 Endo group. There was a statistically significant difference between the ProFile and ProTaper groups (p = 0.0079). The percentage of broken files was 1.7% for the ProFile group, 6.0% for the ProTaper group, and 2.1% for the K3 Endo group. No statistically significant differences were found between these three groups (p = 0.4243).The results of this study showed that these three rotary tapered systems were not significantly different with regard to breakage. There were significantly more distorted files in the ProFile group when compared with the ProTaper group. With regard to distortion, there was no significant difference between the ProTaper and K3 Endo and the ProFile and K3 Endo groups.