Abstract
Purpose: Nickel-titanium (Ni-Ti) orthodontic archwire corrodes under the application of oral fluoride products. This study aimed to develop a thin-film coating for Ni-Ti archwire to prevent surface corrosion by fluoride attack while maintaining its superelasticity and without increasing friction with the bracket.
Methods: A thin yttria (Y2O3) film was deposited onto Ni-Ti archwire using a molecular precursor method. The surface of Y2O3-coated Ti disk was observed by scanning electron microscope (SEM) and its hardness was measured and was analyzed by X-ray photoelectron spectroscopy (XPS). Y2O3-coated Ni-Ti archwires were immersed in acidulated phosphate fluoride (APF) for 30 min, and their corrosion resistance was observed using SEM. Static friction between the archwire and orthodontic bracket was measured using a custom-made apparatus. Three-point bending tests were performed using an original three-point bending apparatus.
Results: The entire archwire surface was coated with Y2O3 without visible peeling or cracks. XPS revealed the presence of the Y2O3 coating. There were no significant differences in micro-Vickers hardness before and after coating. There was no remarkable corrosion of the Y2O3-coated Ni-Ti surface, and the presence of the coated layer was still observed after immersion in APF. There were no significant differences in static friction between Ni-Ti and Y2O3-coated Ni-Ti archwire. Three-point bending tests indicated that Y2O3-coated Ni-Ti archwire can maintain the same superelastic properties as Ni-Ti archwire.
Conclusion: Y2O3-coated Ni-Ti archwire can be applied to orthodontic treatment because of its corrosion resistance to fluoride attack, whilst maintaining the same friction ability and superelasticity as Ni-Ti archwire.
