Tehran University of Medical Sciences Journal of Craniomaxillofacial Research 2345-5489 12 1 2025 08 25 46 53 Manijeh Mohammadian Department of Dental Materials, Faculty of Dentistry, Alborz University of Medical Sciences, Karaj, Iran. Shahin Shahbazpey Department of Periodontology, Faculty of Dentistry, Kerman University of Medical Sciences, Kerman, Iran. Abolfazl Hosseinabadi Department of Orthodontics, Faculty of Dentistry, Kerman University of Medical Sciences, Kerman, Iran. 2025 05 28 2025 07 05 Introduction: This study aimed to evaluate the effects of 0.2% sodium fluoride and Persica mouthwashes on the flexural strength and surface characteristics of nickel-titanium (NiTi) orthodontic wires through an in vitro investigation.  Materials and Methods: Twenty-seven 0.016-inch NiTi wire samples (3cm long) were divided into three groups (n=9/group): distilled water (control), Persica, and 0.2% NaF mouthwash. Wires were immersed for 90 minutes (simulating 3 months of daily use) and subjected to a three-point bending test (0.5mm/min deflection). Surface changes were analyzed via scanning electron microscopy (SEM). Data were compared using ANOVA and Bonferroni tests. Results: Unloading-phase forces, yield strength, and elastic modulus significantly decreased in NaF and Persica groups versus control (p<0.05), with no differences in loading-phase (p>0.05). SEM revealed the highest corrosion in NaF and the lowest in control. No significant differences were observed between NaF and Persica (p>0.05).   Conclusion: Exposure to 0.2% sodium fluoride and Persica mouthwashes adversely affects the mechanical properties and surface integrity of NiTi orthodontic wires. Clinicians should consider the potential implications of prolonged mouthwash use during orthodontic treatment.  Keywords: Mouthwash; Orthodontic wire; Mechanical properties; Corrosion; Nickel-titanium. https://jcr.tums.ac.ir/index.php/jcr/article/view/545 https://jcr.tums.ac.ir/index.php/jcr/article/download/545/440