## 4 Discussion
The EDTA group effectively removed the smear layer but caused a significantly greater decrease in dentin microhardness than the other groups. These findings are consistent with results reported in other studies [64,65]. A notable direct relationship was observed between root dentin calcium reduction and its microhardness. [PERSON] and [PERSON] reported a straightforward linear correlation between dentin hardness and calcium ion concentration [66]. However, all groups had lower microhardness values at 50 \(\upmu\)m and 100 \(\upmu\)m compared to the control group, but values were higher in the EDTA group. This corroborates another study, which concluded that utilizing EDTA 17% can reduce dentin microhardness. This may explain why all experimental groups exhibited significantly higher microhardness than the chelating agents compared to the control group [49]. When comparing the microhardness at 50 \(\upmu\)m and 100 \(\upmu\)m, it showed a lower mean value at 50 \(\upmu\)m than at 100 \(\upmu\)m because there is an inverse relationship between dentin hardness and depth of radicular dentin at the distance between the pulp lumen and cementodentinal junction within the same tooth. The area near the pulp lumen at 50 \(\upmu\)m had low microhardness because of the increased number and width of dentinal tubules, which was associated with a lower amount of peritubular dentin than the area close to the cementodentinal junction at 100 \(\upmu\)m [67]. In the present study, the coronal section had lower dentin microhardness than the middle and apical sections in all groups because of the increased tubular density of coronal dentin compared to middle and apical dentin, reflecting a histological pattern of radicular root canal dentin [68]. Changes in dentin microhardness from the coronal to apical sections are related to changes in mineral amount during different treatment protocols [69]. In the present study, the analysis of the points at 1 mm above and below the midpoint of the root section at the lumen surface showed an increase in the microhardness of root canal dentin after irrigation with IONPs, especially for the MUI group compared with the control group and the EDTA group. This occurred due to the change in calcium/phosphorus ratio in the root lumen due to the effect of iron ions. In contrast, phosphate ions may attract calcium ions to form a satisfactory layer for the nucleation of crystals, resulting in the construction of a calcium-phosphate surface [70]. This study has several limitations. First, the analysis of the antibacterial effect, cytotoxicity, and fracture resistance is based on preliminary data from unpublished work and has not yet undergone peer review. Second, using an external magnetic field to guide the irrigant may present practical challenges in routine clinical settings. Third, this study did not assess long-term effects on dentin structure and canal healing and only assessed the immediate effects (e.g., microhardness or smear layer removal). Consequently, the technique has not been clinically validated, given that it has not yet been tested in actual patients. Future clinical trials are necessary to confirm these findings and evaluate the method's effectiveness and safety in real-world settings.