Objectives. Detailed knowledge of the elusive anatomy of root canals systems is essential for successful endodontics. The current study employed high resolution scanning tomography (µCT) to assess changes in the canals' paths after preparation using 4 NiTi preparation systems.Material and Methods. A commercially availabe µCT scanner (Scanco, Switzerland) was used to analyze 40 extracted maxillary molars. Teeth were scanned before & after 30 canals each were prepared using NiTi K-Files, Lightspeed, ProFile .04 & GT Files. Precise repositioning allowed repeated scanning of specimens after preparation. Dentin volume (V) and surface areas (A) for each canal before & after preparation were calculated using specially developed software. Differences between means were analyzed using repeated measures ANOVA.Results. Mean canal volumes (± SD) & surface areas were 2.30 ± 1.51mm3 & 18.76 ± 7.72mm2 before and 4.39 ± 1.60mm3 & 24.45 ± 6.63 mm2 after preparation. Changes in canal volume and area differed significantly (p Palabras clave: micro computed tomography, root canal, rotary instrumentation