Purpose: This study aimed to compare the influence of root canal preflaring using stainless steel K-files and rotary nickel-titanium (NiTi) PathFiles on the preservation of the original anatomy of the canals. The incidence of canal transportation and apical transportation were evaluated. Methods: A total of 60 root canals obtained from a pool of freshly extracted human mandibular and maxillary molars were divided into two groups. Each sample was placed on a mould, and pre-and post-instrumentation radiographs were taken. The radiographs were scanned and the angles of the root canal curvatures calculated using computer software (SIDEXIS 5.5/5.5×). Superimpositions were performed to calculate the apical root canal transportation. Results: The results were statistically analysed to compare the two techniques. Significant differences (P 0.05) regarding the two parameters evaluated were found between the two different instruments. The PathFile group showed significantly less canal transportation (P = 0.011) and less apical transportation (P 0.001). Conclusions: The results suggest that preflaring with PathFile NiTi rotary files maintained root canal anatomy better than stainless steel hand K-Files in severely curved canals, with curvatures greater than 30 degrees. Schlagwörter: apical transportation, preflaring, root canal preparation, rotary files, stainless steel instruments