Root Microcracks Formation during Root Canal Instrumentation Using Reciprocating and Rotary Files

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The aim of this study was to compare the formation of dentinal cracks with nickel-titanium (NiTi) instruments working in continuous rotation and reciprocating motion. One hundred sixty extracted human mandibular first molars were selected for the study. The mesial roots were resected and mounted in resin blocks with simulated periodontal ligaments. Those teeth were randomly assigned to five groups (n = 32 teeth/group). The first one was treated with K-files and served as control group, and the remaining 128 teeth were divided into 4 groups depending on the root canal preparation technique. Group 2 samples were prepared by sequential ProTaper Universal (PTU), group 3 samples with rotary ProTaper Universal (RPTU), group 4 achieved by the One Shape (OS), and group 5 with the WaveOne (WO) primary files. Roots were then horizontally sectioned at 3, 6, and 9 mm from the apex, and the slices were then observed under a stereomicroscope at ×40 magnification to determine the presence of internal dentinal microcracks. The presence or absence of dentinal defaults was recorded and the statistical analysis was performed by Pearson Chi-square test. The significance level was set at p < 0.05. The study was made in the oral biology and biotechnology research laboratory of the faculty of medical dentistry of Rabat, Morocco. No dentinal defect was seen with the stainless steel hand file (group 1). The manual PTU (group 2), the RPTU (group 3), the OS (group 4), and the WO (group 5) in reciprocating motion caused cracks in 15.6%, 12.4%, 21.9%, and 6.2% of samples, respectively. The highest percentage of dentinal defect was showed in group 4 but without significant difference with the other group (p > 0.05). Dentinal cracks are produced indifferently of motion kinematics. Within the limits of this study and the current literature, such incidence is less with instruments working in reciprocating motion compared with those working in continuous rotation. Manual and rotary NiTi sequential systems showed fewer microcracks than the single file system working by continuous rotation motion.