Canal Transportation and Centring Ability of Different Rotary Files in Continuous or Adaptive Motion: Micro-Computed Tomography Study

Objective: To investigate root canal transportation and centring ability of two rotary nickel-titanium instruments used in continuous rotation or Adaptive Motion. Methods: Twenty extracted human mandibular molars with two separate mesial canals with an angle of curvature ranging from 25° to 50° were selected. The 40 canals were divided in four experimental groups: Mtwo® and Twisted File Adaptive instruments used in continuous rotation (groups 1 and 2 respectively) or in Adaptive Rotary Motion (groups 3 and 4 respectively). Each group consisted of 10 root canals. Specimens were scanned before and after root canal preparation using microcomputer tomography. The degree of root canal transportation and instruments’ centring ability data were analyzed by two-way ANOVA. Results: Twisted File Adaptive instruments showed less transportation than Mtwo in continuous rotation and in Adaptive Motion (p<.0001 for each comparison). Canal transportation was lower using the same instrument in Adaptive Motion than in continuous rotation, but significance level was not achieved (p>.05). No difference was found in the centering ratio between Twisted File Adaptive and Mtwo when the same motion was used (p>.05). However, Twisted File in Adaptive Motion showed higher centering ability and lower canal transportation than Mtwo in continuous rotation (p<.0001). Conclusion: The Twisted File Adaptive instruments were found to produce less root canal transportation but no better centring ability when compared with Mtwo in continuous rotation or Adaptive Motion. The Adaptive Motion alone does not improve canal transportation and centring ability.