Morphological Changes of the Apical Foramen in Curved Root Canals After Use of Different Heat Treated NiTi Rotary Files: A Scanning Electron Microscopy Study

Objective: The present study aimed to evaluate the effect of heat-treated nickel titanium (NiTi) files TruNatomy and XP- Endo Shaper on the major apical foramen deformation and enlargement in curved root canals using area, circularity, and Feret's diameter ratio. Methods: Sixty mesio-buccal roots of maxillary and mandibular molars with Vertucci type II root canal were selected. The teeth were decoronated using a carborundum disc. The roots with a length of 13 mm were measured using a digital caliper.The preoperative scanning electron microscope images of apical roots were taken and then divided into 4 groups. Manual (K file, Mani Tochigi, Japan), ProTaper Universal (PTU, Dentsply Maillefer, Ballaigues, Switzerland), XP-Endo Shaper (XPS;FKG Dentaire SA, La Chaux-de-134 Fonds, Switzerland), and TruNatomy (TRN;Dentsply Sirona, Ballaigues, Switzerland) group. After instrumentation, the post-operative scanning electron microscope images were taken. Surface area, circularity, and Feret's diameter ratio was calculated before and after instrumentation using Image J software. For intergroup comparison of data, student's independent t-test was employed and for intra-group comparison of data, paired t-test was applied. Results: The area after instrumentation increased in all groups but the K file and PTU show statistically significant differences compared to TRN and XPS (p<0.001). The circularity tends towards 0 in K file and PTU and canals became ellipticals after instrumentation. However, TRN and XPS showed no difference. There is no significant difference in the Feret's diameter ratio before and after instrumentation. Conclusion:The enlargement of the majorapical foramen occurs regardless of the type of file system used.The hand K files and PTU result in significant foramen deformation when instrumented up to the major apical foramen. However, TRN and XPS promote minor alterations at the foramen which are not statistically significant.