cone-beam computed tomographic assessment of canal centering ability and transportation after preparation with twisted file and bio race instrumentation.

use of rotary nickel-titanium (niti) instruments for endodontic preparation has introduced a new era in endodontic practice, but this issue has undergone dramatic modifications in order to achieve improved shaping abilities. cone-beam computed tomography (cbct) has made it possible to accurately evaluate geometrical changes following canal preparation. this study was carried out to compare canal centering ability and transportation of twisted file and biorace rotary systems by means of cone-beam computed tomography.thirty root canals from freshly extracted mandibular and maxillary teeth were selected. teeth were mounted and scanned before and after preparation by cbct at different apical levels. specimens were divided into 2 groups of 15. in the first group twisted file and in the second, biorace was used for canal preparation. canal transportation and centering ability after preparation were assessed by nnt viewer and photoshop cs4 software. statistical analysis was performed using t-test and two-way anova.all samples showed deviations from the original axes of the canals. no significant differences were detected between the two rotary niti instruments for canal centering ability in all sections. regarding canal transportation however, a significant difference was seen in the biorace group at 7.5mm from the apex.under the conditions of this in vitro study, twisted file and biorace rotary niti files retained original canal geometry.