Objectives:This study was aimed at comparing three rotatory systems for instrumentation of root canals regarding the prepare of apical third and the dilatation of the middle and cervical points of the canal. K3 (group I), ProTaper (group II) and Quantec (group III) systems were used. Methods:Thirty canals were simulated into a curved shape in acrylic resin blocks and divided up into three groups with different instrumentation procedures according to the different systems. After that, the canals were filled with black ink, photographed and outlined by the projection technique. The assessment of apical prepare was carried out at 6 points of its length by means of the mathematical method by Campos & Campos, whereas the middle and cervical dilation were obtained by measuring the diameter between these points. Results: showed that the highest averages regarding apical prepare were presented by group I, significantly different from groups III and II (p< 0,05 – Scheffe). As for middle and cervical dilation, these were higher in group II, followed by group I. No difference in cervical dilation was found between groups I and II (p> 0,05 – Scheffe). By considering all measures, group I presented higher averages with significant difference for groups II and III (p< 0,05 – Scheffe). Conclusions:We have concluded that, according to the methodology, K3 system produced more regular prepares, with no deviation and progressive taper accounted for by a better relation between apical prepare tapering and dilation of middle and cervical points.