COMPARATIVE EVALUATION OF DENTINAL MICROCRACK FORMATION FOLLOWING ROOT CANAL PREPARATION WITH HAND K-FILES AND THREE CONTEMPORARY NITI ROTARY SYSTEMS: AN IN VITRO STUDY

Abstract

Background: Root canal instrumentation may generate dentinal microcracks that weaken the root and increase susceptibility to vertical fracture. This study compared dentinal defects produced by stainless-steel hand K-files and three contemporary nickel–titanium rotary systems. Methods: Seventy-five extracted single-rooted mandibular premolars were randomly allocated into five groups (n=15): uninstrumented control, hand K-file, Neoendo Flex, HyFlex EDM, and TruNatomy. Following canal preparation, roots were horizontally sectioned at 3, 6, and 9 mm from the apex. Sections were examined stereomicroscopically and classified as having no defect, an incomplete crack, or a complete crack. Intergroup comparisons were performed using the chi square test. Results: Dentinal defect distribution differed significantly among groups at the coronal (χ²=20.66, p=0.008) and middle levels (χ²=22.00, p=0.005). TruNatomy showed the most favourable results, with 80% of specimens remaining defect free at both levels and no complete cracks. At the middle level, complete cracks occurred most frequently with hand K files (80%), while HyFlex EDM predominantly produced incomplete cracks (80%). No significant intergroup difference was found at the apical level (χ²=1.19, p=0.880), where no complete cracks were detected. Conclusion: The instrumentation system influenced dentinal microcrack formation. TruNatomy demonstrated better preservation of root dentin, particularly in the coronal and middle thirds. However, the occurrence of defects in uninstrumented specimens indicates that extraction or specimen preparation may have influenced the findings.