Effects of self-ligating brackets on the surfaces of stainless steel wires following clinical use: AFM investigation.

In orthodontic treatment, the frictional force between the archwire and bracket reduces the effectiveness of orthodontic treatment. The frictional force is affected not only by the geometry of the self-ligating brackets but also by physical changes between the bracket slots and archwire surfaces during sliding movement. This study examined quantitatively the effect of self-ligating treatments on the surfaces of stainless steel (SS) archwires during tooth movement in vivo by atomic force microscopy. Orthodontic 0.019″ × 0.025″ SS archwires after clinical use with the first bicuspid-extraction treatment were employed using the Damon 3MX(®) SS self-ligating brackets, Clippy-C(®) ceramic self-ligating brackets, and Kosaka(®) SS brackets. Intact SS archwires were used as the control group. All SS archwires after clinical use showed severe scratches and significantly higher roughness caused by frictional interactions between the brackets and archwires (p < 0.0001 vs. control). The descending order of surface roughness was the SS archwires treated, with ceramic self-ligating brackets, with conventional SS brackets, and with SS self-ligating brackets (p < 0.001). These findings suggest that an orthodontic treatment with SS self-ligating brackets may require smaller orthodontic forces than that with ceramic self-ligating brackets or conventional SS brackets.