Objective: The aim of this study was to decrease the friction between orthodontic brackets and arch wires by using aluminum oxide (Al₂O₃), titanium nitride (TiN), and chromium nitride (CrN) medical coating materials. The coatings’ resistance to intra-oral conditions was evaluated.
Methods: Stainless steel canine brackets, 0.016’’ round nickel titanium and 0.019 x 0.025’’ stainless steel arch wires were coated with Al₂O₃, TiN, and CrN using the Radio Frequency Sputtering method. The coated materials were examined using scanning electron microscopy, an x-ray diffractometer, atomic force microscopy, and surface profilometry. A modified tribometer was used to measure the in vitro coefficients of friction (CoFs) of the coated and uncoated materials. Samples were subjected to thermal cycling and in vitro brushing tests, and the effects of simulated intra-oral conditions on the coating structure were evaluated with scanning electron microscopy.
Results: Coating both the metal bracket and nickel titanium arch wire with Al₂O₃ reduced the CoFs of the bracket arch wire combination (p < 0.01). Coating the bracket and stainless steel arch wire with Al₂O₃ and TiN resulted in statistically significantly lower CoFs (0.207 and 0.372, respectively) compared to the uncoated bracket and arch wire combination (0.552) (p < 0.01). The frictional wear, thermal, and brushing tests did not deteriorate the overall quality of Al₂O₃ coatings, but some small peeled areas were evident for TiN coatings and comparatively larger peeling was observed for CrN.
Conclusion: The CoFs between the metal brackets and arch wires could be decreased with Al₂O₃ and TiN thin film coatings.

Keywords: Thin film coating, Coefficient of friction, Bracket, Wire