Effects of Abrasive Flow Finishing on the Surface Quality, Frictional Resistance, and Biological Performance of Brackets

Objectives This study aims to investigate the effects of abrasive flow finishing (AFF) on the surface quality, frictional resistance, and biological performance of orthodontic brackets. Methods Stainless-steel brackets were randomly allocated into blank, control, and AFF groups. The blank group was left untreated. The control group underwent conventional magnetic polishing, while the AFF group was treated with AFF. Surface morphology was observed using scanning electron microscopy. Surface roughness at the micro- and nanoscale was investigated via 3D optical profilometry and atomic force microscopy, respectively. The arithmetic average roughness (Ra) and root mean square roughness (Rq) were analysed. The changes in slot dimensions were evaluated. Frictional resistance was determined using a universal testing machine. Biological performance was evaluated via bacterial adhesion and in vitro calculus formation assays. Results The AFF group presented a mirror-like finish. Scanning electron microscopy micrographs exhibited the smooth and uniform surface in outer and slot areas in the AFF group, while the control group showed obvious defects and pits within slots. 3D optical profilometry and atomic force microscopy demonstrated the smooth and regular surface topography in the AFF group. Quantitative analysis showed that Ra and Rq values of the slot area in the AFF group were significantly lower than those of blank and control groups. There were no significant changes in slot dimensions following AFF treatment. The kinetic friction force was significantly reduced in the AFF group. Furthermore, AFF treatment inhibited bacterial adhesion and calculus-like mineral deposition on brackets. Conclusion AFF treatment effectively reduced the surface roughness of orthodontic brackets, especially within slot area, outperforming conventional magnetic polishing. This improvement further minimized frictional resistance and inhibited bacterial adhesion and calculus-like mineral deposition. Clinical relevance This study demonstrates that AFF is a superior post-processing technique for orthodontic brackets.