Comparative Evaluation of Dentinal Microcrack Formation Following Root Canal Preparation With Three Single-File Nickel-Titanium Systems

Introduction: Dentinal microcracks may develop during mechanical root canal preparation, compromising the structural integrity of root-filled teeth.This study compared dentinal microcrack formation following preparation using three single-file nickel-titanium systems.Materials and Methods: This in vitro study was conducted on 36 extracted single-rooted mandibular premolars, which were randomly allocated into three groups (n = 12): One-Shape, Flexer ONE, and HyFlex EDM.Micro-computed tomography was used to evaluate dentinal microcracks before and after instrumentation.Incomplete microcracks, complete microcracks, craze lines, and total cracks were assessed.Two-factor mixed analysis of variance with Bonferroni-adjusted post-hoc comparisons was used for statistical analysis, with significance set at p < 0.05.Results: Instrumentation resulted in a significant increase in incomplete and complete microcracks, craze lines, and total cracks across all three groups (all p < 0.001).The between-group effect was significant for total cracks (p = 0.004), while the group × time interaction was also significant (p = 0.004).Post-hoc analysis demonstrated a significant difference in total crack formation between the One-Shape and HyFlex EDM (mean difference = 2.50, p = 0.002).Postoperatively, One-Shape showed significantly fewer total cracks than Flexer ONE (p = 0.016) and HyFlex EDM (p < 0.001), whereas the difference between Flexer ONE and HyFlex EDM was not significant (p = 1.000).Conclusion: All three single-file systems increased dentinal microcrack formation after root canal preparation.Although differences were not significant for individual crack categories, the total crack formation differed among the systems, with One-Shape demonstrating the lowest postoperative crack formation.