Effects of Different Irrigation Protocols on the Surface Morphology and Elemental Composition of Super One File Nickel-Titanium Instruments.

Background: Nickel-titanium (Ni-Ti) instruments are continuously exposed to irrigating solutions during root canal preparation, which may affect their surface integrity. Evidence regarding the combined morphological and elemental effects of contemporary irrigation protocols on heat-treated single-file systems remains limited. This study evaluated the effects of different irrigation protocols on the surface morphology and elemental composition of Super One File Ni-Ti instruments using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Methods: Thirty Super One File instruments (size 25/.04) were randomly allocated to three groups: distilled water (DW), a sequential NaOCl-EDTA-NaOCl irrigation protocol (NEN), and a NaOCl/HEDP continuous chelation protocol. Instruments were continuously rotated in the assigned solution for 20 min. Surface morphology was assessed by SEM and elemental composition by EDS. SEM data were analysed using the Fisher-Freeman-Halton exact test, whereas EDS data were analysed using linear mixed-effects models with post hoc pairwise comparisons (α = 0.05). Results: SEM analysis revealed protocol- and region-dependent differences in surface alterations. The NEN group showed significantly higher corrosion and pitting frequencies than the DW group in selected regions, whereas no significant differences in these outcomes were detected between the NEN and HEDP groups. EDS analysis showed significant protocol × region interactions for all elements except Cl. These differences were most pronounced in the coronal region, where the HEDP group exhibited lower Ni and Ti and higher O, P, Na, and Ca levels than the DW and NEN groups. Conclusions: The tested irrigation protocols produced distinct, region-dependent surface responses in Super One File instruments, highlighting the potential influence of irrigation chemistry on Ni-Ti instrument surfaces under controlled experimental conditions. The clinical and mechanical implications of these alterations remain to be established.