This study was aimed to use micro-computed tomography (-CT) to evaluate the canal shaping properties of three nickel-titanium instruments, Self-Adjusting File (SAF), Reciproc, and Revo-S rotary file, in maxillary first molars. Thirty maxillary molars were scanned preoperatively by using micro-computed tomography (-CT) scans at 13,68m resolution. The teeth were randomly assigned to three groups (n=10). The root canals were shaped with SAF, Reciproc, and Revo-S, respectively. The shaped root canals were rescanned. Changes in canal volumes and surface areas were compared with preoperative values. The data were analyzed using Kruskal-Wallis and Conover's post hoc tests, with p<.05 denoting a statistically significant difference. Preoperatively canal volumes and surface area were statistically similar among the three groups (p>.05). There were statistically significant differences in all measures comparing preoperative and postoperative canal models (p=0.0001). These differences occurred after instrumentation among the three experimental groups showed no statistically significant difference for volume (p>.05). Surface area showed the similar activity in buccal canals in each of the three techniques whereas no statistically significant difference was detected among surface area, the SAF, and the Revo-S in the palatal (P) canal. Each of three shaping system showed the similar volume activity in all canals, but SAF and Revo-S provided more effectively root planning in comparison with Reciproc in P canal. SCANNING 37:218-225, 2015. (c) 2015 Wiley Periodicals, Inc.