Surface ultrastructure and mechanical properties of three different white-coated NiTi archwires

The recent trend in orthodontic treatment is to apply esthetic materials to orthodontic appliances with adequate clinical performance. The aim of this study was to investigate the ultrastructure (surface roughness) and mechanical properties (load-deflection curve) of three as-received, white-coated superelastic nickel-titanium (NiTi) archwires using atomic force microscopy (AFM) and modified three-point bending test assessments, respectively. Three representative esthetic NiTi archwires were used, silver-platinum- and polymer-coated NiTi Natural Dany (Dany group), epoxy resin-coated Orthoforce Ultraesthetic™ (Ultra group), and Teflon®-coated Perfect (Perfect group). Uncoated metallic areas of each wire were used as controls. The diameter of the Perfect archwire was significantly larger than that of other archwires. The Dany and Ultra groups showed more deflection than the Perfect group. The hysteresis area of the Dany and Ultra groups showed approximately two- and fourfold increases compared to the control and the Perfect group. The Dany group (2037.5 ± 527.3 nm) had the highest peak-to-peak surface roughness in the coated areas, followed by the Ultra group (811.1 ± 407.5 nm) and the Perfect group (362.7 ± 195.8 nm). However, reverse nanostructural changes in the surface roughness were observed in the uncoated metallic areas. The results suggested that the load-deflection properties and the surface roughness of superelastic NiTi archwires were affected directly by the coating materials. Although the efficiency of orthodontic treatment was affected by various factors, when only considering the frictional force and mechanostructural properties, the epoxy resin-coated Orthoforce Ultraesthetic™ archwires were the most effective for orthodontic treatment.