Effects of Fluoride on NiTi Orthodontic Archwires: An X-ray Diffraction Study

Objective: To explore the changes in nickel-titanium (NiTi) archwires after exposure to fluoride-containing acetic acid solutions. Materials and methods: Preformed rectangular NiTi wires were immersed in either an acidulated fluoride solution, a neutral fluoride solution or distilled water (control) for 1.5 hours at 37°C. After immersion, the unloading force values at four deflection points were measured by three-point bending test. Scanning electron microscopy and X-ray diffraction analysis were also performed to characterize the effects of the fluoride exposure on the wire. Results: Unloading force values of NiTi orthodontic wires were significantly decreased after exposure to both fluoride solutions (p < 0.001). Corrosive changes in surface topography were observed for both fluoride solutions. Wires exposed to acidic fluoride appeared as more severely affected. X-ray diffraction analysis showed no change in crystal lattice of NiTi wires in both solutions. Conclusion: The results suggest that using topical fluoride agents with NiTi wire could decrease the functional unloading mechanical properties of the wire and contribute to prolonged orthodontic treatment.