## 1 Introduction
These attributes make them interesting for technological applications in biological and medicinal fields [22], including for imaging and diagnostics, where they are used in magnetic resonance imaging (MRI) probes and positron emission tomography (PET) [23; 24]; for improving combination therapy (alongside chemotherapeutic drugs); as hyperthermia factors [25]; and for magnetic separation, drug delivery [18; 26; 27], iron detection, and cancer treatment [28]. The low cytotoxicity of IONPs, as well as their ability to produce a magnetic response under an external magnetic field, can improve their application in the biomedical field [29]. In 2018, [PERSON] et al. suggested that uncoated magnetite nanoparticles or those coated with amino acids up to a concentration of 373 \(\mu\)g/mL showed no cytotoxicity [30]. Another study showed that IONPs functionalized with tri-sodium citrate solution have no cytotoxicity for fibroblasts at concentrations lower than 0.08 mg/mL [31]. This is consistent with the present study's unpublished results, which recorded no toxic effect up to 312.5 \(\mu\)g/mL at 24, 48, and 72 h. It has been suggested that IONPs, at lower concentrations, do not harm cellular structures [32]. Metal oxide nanoparticles, including magnetite, have different mechanisms of antibacterial action. The first mechanism involves their small size, being smaller than bacterial pores. This improves their ability to access the cell membrane, resulting in continuous destructive activity. By penetrating the cytoplasmic membrane, they can interfere with nucleic acid or protein synthesis and disrupt the functional activity of the cell [33; 34; 35], thereby enhancing their antibacterial effects. The second mechanism that accentuates their antibacterial activity is the formation of reactive oxygen species (ROS) from ferrous ions, which includes superoxide radicals, hydroxyl radicals, hydrogen peroxide, and singlet oxygen free radicals. This occurs through the Fenton reaction, which can damage bacterial DNA, compromise lipids and proteins through oxidative stress, and restrict or limit further growth of the organism [36; 37]. The third mechanism involves static electricity. In an experimental study, positively charged IONPs may be attracted to the negative charge on the surface of _E. faecalis_ bacteria biofilm. When guided through an external magnetic field, the IONPs can eradicate biofilm from the treated root canal wall, preventing acidic formation and subsequently causing bacterial cell death through physical damage [38]. In this study, a dental irrigant incorporating IONPs under the control of an external magnetic field was developed to improve the microhardness of root canal systems without requiring extensive canal shaping. A simulated irrigant solution was tested to evaluate the influence of a magnetic field in mimicking clinical conditions. This approach demonstrated a potential protocol for avoiding conventional instrumentation techniques and the loss of unnecessary root structure. A magnet's external field was applied to root canal dental walls, and an IONPs solution was agitated inside the root canal space. This study aimed to investigate the optimum effect of IONPs in enhancing hardness and identify the concentration of ions in the root canal walls. The null hypothesis states that there are no differences among all the irrigant protocols and the no-treatment group, and that the combination of magnetic activation with ultrasonics to agitate the IONP irrigant in the root canal space does not preserve or enhance dentin microhardness compared to other groups.