Effect of anodization on friction behavior of β‑titanium orthodontic archwires

To evaluate the effects of anodization on the friction behavior of beta-titanium (β-Ti) orthodontic archwires in conventional or self-ligating brackets in vitro.

β‑Ti archwires (0.018 × 0.025 inch) pre- and postanodization were tested in combination with 0.022-inch stainless steel conventional and self-ligating brackets. The surface composition and oxide thickness of the β‑Ti archwires pre- and postanodization were measured using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). Detailed surface topography and roughness were assessed using atomic force microscopy (AFM). Surface topographies of the β‑Ti archwires pre- and postanodization were examined using scanning electron microscopy (SEM). Friction was measured using a universal testing machine; the data were statistically analyzed.

Postanodization, the identified titanium oxide layer on the surface of the β‑Ti archwires increased in thickness from 10 to 100 nm; at the same time, the values for surface roughness were significantly reduced by half (p < 0.001). The archwire surfaces post anodization were harder and had fewer scratches after the friction test. Anodization significantly reduced 23.77% of the static (p < 0.01) and 25.61% of the kinetic (p < 0.001) friction of the β‑Ti archwires in conventional brackets, while it significantly reduced 85.71% of the static and 84.38% of the kinetic friction (p < 0.01) in self-ligating brackets.

Anodization reduced the β‑Ti archwire friction, which was particularly more effective in combination with self-ligating brackets. The friction reduction via anodization could be attributed to the increased thickness, surface hardness, and decreased surface roughness of the titanium oxide layer.