LAUSR

Aims and Objectives: The aim of this study was to assess crack formation using two different cutting motions (rotation and reciprocation) in nickel–titanium rotary instrument. Materials and Methods: One hundred extracted human mandibular incisors were selected for this study. Before root canal instrumentation, low-speed saw (under water cooling) was used to section the tooth horizontally at 3, 6, and 9 mm from the apex of 0.1 mm. A digital stereomicroscope at ×25 magnification with a cold light source was used to observe the slices. Then all teeth were placed again inside the mold. Samples were classified according to the system used into the following groups: Group 1: negative control, Group 2: the ProTaper Next files, Group 3: a primary reciprocating WaveOne Gold file, Group 4: a small reciprocating WaveOne Gold followed by primary reciprocating WaveOne Gold file, and Group 5: OneShape rotary file. Samples were scanned by using a digital stereomicroscope to detect crack formation. Results: Apical level: WaveOne Gold (primary) group showed the highest prevalence of cracks. Middle level: OneShape group showed the highest prevalence of cracks followed by WaveOne Gold (small and primary) group. Coronal level: The five groups showed no statistically substantial difference in the presence of cracks. Conclusion: All rotary systems can lead to the crack formation.