Improvement of orthodontic friction by coating archwire with carbon nitride film

► CNx film is coated on the surface of archwire to reduce wire-bracket friction in orthodontic application. ► The CNx film has sp2 carbon dominated structures and diversiform bonds coexist in the film. ► This CNx film with sp2 rich structures remarkably reduces the wire-bracket friction both in ambient air and in artificial saliva. ► The reduction of friction of the CNx coated wire is more significant at large angulation than that at small angulation.