Effect of Fluoride Prophylactic Agents on the Mechanical Properties of Nickel-Titanium Wires: An in vitro Study

Abstract

Titanium-based alloys have high corrosion resistance because they form a thin, stable oxide layer. Nevertheless, fluoride prophylactic agents can cause corrosion and associated discoloration of titanium-based orthodontic wires. Objective: The purpose of this investigation was to study the effects of fluoride prophylactic agents on the mechanical properties of nickeltitanium (NiTi) and copper-nickel-titanium (Cu-NiTi) orthodontic archwires. Materials and methods: Preformed rectangular NiTi and Cu-NiTi wires were immersed in either an acidulated fluoride agent, a neutral fluoride agent, or distilled water (control) for 1.5 hours at 37°C. After immersion, the loading and unloading elastic modulus and yield strength of the wires were measured with a 3-point bend test in a water bath at 37°C, in accordance with the criteria in the current American National Standard/ American Dental Association Specification No. 32 for Orthodontic Wires (2000). Scanning electron microscopy was also used to characterize the effects of the fluoride treatment on the wire topography. Results: The results showed that unloading mechanical properties of both the NiTi orthodontic wires were significantly decreased after exposure to both fluoride agents [one-way analysis of variance (ANOVA) and Dunnett’s post-hoc,  = 0.05]; corrosive changes in surface topography were observed for both wires, with Phos-Flur gel creating more detrimental effects. 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.