The study compared changes to canal curvature and incidence of canal aberrations after preflaring with hand K-files or with nickel-titanium rotary PathFile in S-shape Endo Training Blocks. The influence of the operator's expertise was also investigated. One hundred training blocks were colored with ink, and preinstrumentation images were acquired digitally. Preflaring was performed by an endodontist with PathFile (group 1) and hand stainless steel K-files #10-15-20 (group 2); an inexpert clinician performed preflaring with PathFile (group 3) and hand stainless steel K-files (group 4). Preinstrumentation and postinstrumentation images were superimposed to evaluate the outcomes investigated. Differences in canal curvature modification and incidence of canal aberration were analyzed with the Kruskall-Wallis plus post hoc tests and by the Monte Carlo method, respectively, (P < .05). The PathFile groups demonstrated significantly less modification of curvature (P < .001) and fewer canal aberrations (P < .001). No expertise-related difference was found within instrument groups (P > .05), whereas the inexpert clinician produced more conservative shaping with Pathfiles than did the expert with manual preflaring (P < .01).