Abstract
OBJECTIVE: The aim of the study was to evaluate the surface areas and volumes of HyFlex EDM (HEDM) nickel-titanium (NiTi) files before and after multiple uses in mandibular molar root canal preparation. MATERIALS AND METHODS: Twelve HEDM files with sizes of 10/.05 and 25/.08 were evaluated by micro-CT before and after a single use or multiple uses in root canal preparation. The mesiobuccal and mesiolingual root canals of thirty-six human mandibular molar teeth were instrumented using twelve 10/.05 (300 rpm and 1.8 Ncm) and twelve 25/.085 Ncm) HEDM files according to the manufacturer's recommendation. HEDM files were evaluated using micro-CT at four different timelines: 1) Intact file, 2) After instrumentation of one canal, 3) After instrumentation of two canals, and 4) After instrumentation of three canals. Each group's volume and surface area were analyzed by applying Friedman's test. Each group comparison was assessed using the Wilcoxon signed-rank test with Bonferroni correction. RESULTS: Intact HEDM 10/.05 and HEDM 25/.08 files showed significantly larger volumes and surface areas compared to the used instruments (p < 0.05). CONCLUSIONS: A significant decrease in the volume and surface area of the NiTi files was observed as the number of uses increased regardless of the file group. These findings emphasize the importance for clinicians to understand the structural changes in HEDM files during repeated use to ensure safe instrument reuse and prevent endodontic treatment failure.