In order to reduce frictional resistance between archwire and bracket during orthodontic tooth movement, carbon nitride (CNx) thin films were deposited on the surface of archwires with ion beam assisted deposition (IBAD). The energy-dispersive X-ray spectrometer (EDS) analysis showed that the CNx film was successfully deposited on the surface of the orthodontic wires. X-ray photoelectron spectroscopy (XPS) analysis suggested that the deposited CNx film was sp(2) carbon dominated structures, and diversiform bonds (N-C, N C, et al.) coexisted in the film. The friction tests indicated that the CNx film significantly reduced the wire-bracket friction both in ambient air and in artificial saliva. The sp(2)C rich structure of the CNx film as well as its protection function for the archwire was responsible for the low friction of the wire-bracket sliding system. (C) 2011 Elsevier B.V. All rights reserved.