Effect of fluoride toothpaste on the physical, chemical, and mechanical properties of NiTi orthodontic archwires: an in vitro study

Fluoride is used to prevent both primary and secondary dental caries. Using fluoride-containing products is strongly correlated with the corrosion of orthodontic archwires. The aim of this study was to examine the physical, chemical, and mechanical properties of nickel-titanium (NiTi) orthodontic archwires affected by exposure to fluoride-containing toothpaste. According to the study protocol, sixty round 0.014″ diameter archwires were tested. The study sample consisted of three groups, each containing twenty archwires. One experimental group used toothpaste without fluoride, while the other used toothpaste containing 1448 ppm fluoride. The control group was not exposed to any toothpaste. Both study and control groups were divided into two subgroups, incubated for 120 min and 240 min at 37 °C. Study groups were incubated in artificial saliva mixed with toothpaste, while the control group was immersed in distilled water. Surface topography analysis was performed by scanning electron microscopy (SEM), and images were taken at 2,500×, 5000×, and 10,000× magnification. The chemical properties were evaluated using energy-dispersive X-ray spectroscopy (EDS). The mechanical properties were assessed using a universal testing machine with a tensile test. Statistical analysis was performed using SPSS 29.0. Compared with the non-fluoride and control groups, the fluoride group archwires increased the amount of corrosion and caused more surface degradation with deeper dark scratches. Compared with non-fluoride and fluoride groups, the surfaces of unused wires are less prone to surface irregularities. The strength analysis revealed that the applied force remained consistent across all study groups at the point of archwire breakage, with no statistically significant differences. However, after 240 min of incubation, the fluoride toothpaste group exhibited a significantly greater decrease in elongation compared to the other groups (42.2%) (p < 0.001). Moreover, chemical analysis after 240 min of exposure revealed the greatest decreases in titanium ions (19.23%) and nickel ions (15.97%) in the fluoride group compared to the other groups (p > 0.05). Fluoride group archwires exhibited more corrosion, surface degradation, the weakest elasticity, and fewer titanium and nickel ions. Prolonged exposure to toothpaste also affects the mechanical properties of NiTi archwires, significantly reducing elongation, suggesting that archwires should be replaced more frequently during treatment.