Changes in ultrastructure and properties of bracket slots after orthodontic treatment with bicuspid extraction

This study examined the effects of an orthodontic treatment using a bicuspid extraction on the surface roughness and mechanical properties of stainless steel (SS) brackets adjacent to the extraction space. Four experimental groups were employed; groups 1 and 2 used the Archist(®) SS brackets before and after the extraction treatment, respectively, and groups 3 and 4 used the Victory(®) SS brackets before and after the extraction treatment, respectively. The slot surfaces of the bracket were scanned in air at a resolution of 512 × 512 pixels with a scan speed of 0.8 line/s. The visco-elasticity of the bracket slot was determined from the force-distance curves of atomic force microscopy. The orthodontic treatment with bicuspid extraction led to a significant increase (p<0.0001) in surface roughness in both groups. In particular, the Archist(®) SS brackets showed more changes than the Victory(®) SS brackets (p<0.0005). However, there was no significant difference in properties of the Victory(®) and Archist(®) brackets between before and after treatment. This suggests that the orthodontic treatment with bicuspid extraction is more responsible for the changes in surface roughness than the properties of the brackets.