Incidence of Dentinal Cracks after Root Canal Preparation with Twisted File Adaptive Instruments Using Different Kinematics.

Introduction: The purpose of the present study was to assess the effect of root canal instrumentation using Twisted File Adaptive instruments (Axis/SybronEndo, Orange, CA) with different kinematics (adaptive motion, 90 degrees clockwise [CW]-30 degrees counterclockwise [CCW], 150 degrees CW-30 degrees CCW, 210 degrees CW-30 degrees CCW, and continuous rotation) on crack formation. Methods: One hundred five mandibular central incisor teeth were selected. Fifteen teeth were left unprepared (control group), and the remaining 90 teeth were assigned to the 5 root canal shaping groups as follows (n = 15): adaptive motion, 90 degrees CW-30 degrees CCW, 150 degrees CW-30 degrees CCW, 210 degrees CW-30 degrees CCW, continuous rotation, and hand file. All the roots were sectioned horizontally at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling, and the slices were then viewed through a stereomicroscope at 25x magnification. Digital images of each slice were captured using a camera to determine the presence of dentinal cracks. Results: No cracks were observed in the control group, and the continuous rotation group had more cracks than the reciprocation groups (90 degrees CW-30 degrees CCW, 150 degrees CW-30 degrees CCW, and 210 degrees CW-30 degrees CCW) (P<.05). Both the continuous rotation and adaptive motion groups had significantly more dentinal cracks than the hand file group (P<.05). Regarding the different sections (3, 6, and 9 mm), there was a significant difference between the experimental groups at the 9-mm level (P<.05). Conclusions: The incidence of dentinal cracks is less with TF Adaptive instruments working in 210 degrees CW-30 degrees CCW reciprocating motion compared with working in continuous rotation and adaptive motion.