THE KOREAN JOURNAL of Original Article ORTHODONTICS pISSN 2234-7518 • eISSN 2005-372X https://doi.org/10.4041/kjod.2021.51.4.270 Effectiveness of medical coating materials in decreasing friction between orthodontic brackets and archwires Nursel Aricia Objective: The aim of this in vitro study was to evaluate the changes in friction b Berat S. Akdeniz between orthodontic brackets and archwires coated with aluminum oxide (Al2O3), Abdullah A. Oza titanium nitride (TiN), or chromium nitride (CrN). In addition, the resistance Yucel Gencerc of the coatings to intraoral conditions was evaluated. Methods: Stainless steel Mehmet Tarakcic canine brackets, 0.016-inch round nickel–titanium archwires, and 0.019 × a Selim Arici 0.025-inch stainless steel archwires were coated with Al2O3, TiN, and CrN using radio frequency magnetron sputtering. The coated materials were examined using scanning electron microscopy, an X-ray diffractometer, atomic force microscopy, and surface profilometry. In addition, the samples were subjected to thermal cycling and in vitro brushing tests, and the effects of the simulated a intraoral conditions on the coating structure were evaluated. Results: Coating Department of Orthodontics, Faculty of Dentistry, Ondokuz Mayıs University, of the metal bracket as well as nickel–titanium archwire with Al2O3 reduced the Samsun, Turkey coefficients of friction (CoFs) for the bracket–archwire combination (p < 0.01). bDepartment of Orthodontics, Faculty When the bracket and stainless steel archwire were coated with Al2O3 and TiN, of Dentistry, Kırıkkale University, the CoFs were significantly lower (0.207 and 0.372, respectively) than that Kırıkkale, Turkey recorded when this bracket–archwire combination was left uncoated (0.552; cMaterials Science and Engineering p < 0.01). The friction, thermal, and brushing tests did not deteriorate the Department, Engineering Faculty, overall quality of the Al2O3 coatings; however, some small areas of peeling were Gebze Technical University, Kocaeli, evident for the TiN coatings, whereas comparatively larger areas of peeling were Turkey observed for the CrN coatings. Conclusions: Our findings suggest that the CoFs for metal bracket–archwire combinations used in orthodontic treatment can be decreased by coating with Al2O3 and TiN thin films. [Korean J Orthod 2021;51(4):270-281] Key words: Thin film coating, Coefficient of friction, Bracket, Archwire Received October 15, 2020; Revised December 18, 2020; Accepted December 24, 2020. Corresponding author: Selim Arici. Professor, Department of Orthodontics, Faculty of Dentistry, Ondokuz Mayıs University, Atakum 55139, Samsun, Turkey. Tel +90-532-4367923 e-mail [email protected] How to cite this article: Arici N, Akdeniz BS, Oz AA, Gencer Y, Tarakci M, Arici S. Effectiveness of medical coating materials in decreasing friction between orthodontic brackets and archwires. Korean J Orthod 2021;51:270-281. © 2021 The Korean Association of Orthodontists. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 270 Arici et al • Coating and friction INTRODUCTION archwires and SS brackets using the plasma-based ion implantation/deposition method.9,20,25 Controlled mechanical forces are used in orthodontics Several coating techniques and materials have been to create a biologic response to move the teeth. Al- used with the objective of improving the surface proper- though several mechanical systems are available, edge- ties of orthodontic appliances. For instance, a coating wise mechanics, which involve the sliding of brackets technology known as the electrostatic powder technique or tubes through an archwire, are the most popular.1 As was used to apply epoxy paint to NiTi wires, and it was observed in all mechanical systems, friction is gener- found that the coating resulted in reduced friction rela- ated at the point of contact between the bracket and tive to that without coating.26 Another coating tech- archwire when teeth are moved through the archwire nique, physical vapor deposition, was used to coat beta during treatment using sliding mechanics. This friction titanium orthodontic archwires with titanium aluminum is caused by the contact between the wire and the sur- nitride and tungsten carbide/carbon for the assessment face of the bracket slot, binding between the wire and of frictional properties, the surface morphology, and the corners of the bracket, and notching of the wire as the load deflection rate.18 Radio frequency (RF) magne- a result of permanent deformation at the wire–bracket tron sputtering is another technique used for coating corner interface.2 Friction can occasionally slow or even orthodontic materials. This technique removes surface stop tooth movement, and orthodontic tooth movement atoms from a solid cathode (target) by bombarding it occurs only when the applied forces can adequately with positive ions from an inert gas discharge; then, it overcome the frictional force between the bracket and deposits the surface atoms on the surface to form a thin archwire.3 Studies have shown that up to 60% of the film.27 RF magnetron sputtering is an effective technique applied force could be lost because of friction during because of the inherent versatility, low-temperature thin sliding mechanics.4-6 For optimal tooth movement and film deposition, and uniform surface coating.28,29 Using tissue responses, the amount of applied force should be this technique, a thin layer of photocatalytic titanium such that it maximizes tooth movement without irre- dioxide was applied to SS orthodontic brackets in order versible side effects.5-7 to utilize the antiadhesive and antibacterial properties of In orthodontic treatment, the friction force is affected this compound.30 This technique was also used to coat by several factors such as the width and depth of the NiTi orthodontic wires with titanium in order to assess bracket slot, bracket–archwire angulation, shape and deterioration of the superelasticity of such wires, and it size of the archwire, method of ligation, interbracket was concluded that this coating method has potential distance, level of bracket slots between adjacent teeth, for application in the orthodontic field.31 forces applied for retraction, and biological variables.8,9 Although some of the surface treatments and coatings The surface characteristics of orthodontic materials also described above can decrease the coefficients of friction affect the friction force between the bracket and arch- (CoFs), most had other drawbacks such as low resistance wire during treatment with fixed appliances.10 Different to challenging intraoral conditions, high frictional wear, materials with different frictional characteristics, such and delamination or wear of the coating.32 Thus far, at- as stainless steel (SS), gold, chromium–nickel alloy, tita- tempts at improving the mechanical properties of orth- nium, polycarbonate, aluminum oxide or alumina (Al2O3), odontic archwires using surface treatment and coating and zirconia, are used to manufacture brackets.11-14 techniques have been somewhat satisfactory. However, However, SS brackets and archwires have been shown to limited studies have evaluated changes in the frictional produce the least friction.12,15-17 Therefore, metal slots properties of brackets and archwires coated with the were placed in ceramic brackets to reduce the frictional same material. Therefore, the aim of this in vitro study resistance between the archwire and bracket.12-14 Re- was to evaluate the changes in friction between SS orth- search has accordingly targeted different approaches, odontic brackets and NiTi and SS archwires coated with including surface treatments and coatings to further Al2O3, titanium nitride (TiN), or chromium nitride (CrN). reduce friction between the bracket and archwire.18-21 Moreover, the resistance of the coatings in simulated Surface treatment techniques such as electrolytic intraoral conditions was evaluated. The null hypothesis treatment and ion implantation have been used to was that coating of SS orthodontic brackets and NiTi modify the surfaces of orthodontic metal brackets and and SS archwires with Al2O3, TiN, or CrN does not affect archwires.22,23 In one study, the surfaces of nickel–tita- the in vitro CoFs for the bracket–archwire combination. nium (NiTi), beta titanium, and SS wires were modified by a polytetrafluoroethylene (teflon) coating applied MATERIALS AND METHODS using the ion implantation technique.24 In other studies testing friction and other mechanical properties, dia- Materials mond-like carbon films were deposited on NiTi and SS In this in vitro study, Al2O3, TiN, and CrN were used www.e-kjo.org https://doi.org/10.4041/kjod.2021.51.4.270 271 Arici et al • Coating and friction as coating materials for 50 0.016-inch round, heat-ac- in the presence of argon and nitrogen gases (Table 1). tivated NiTi arch wires (3M Unitek, Monrovia, CA, USA), 50 0.019 × 0.025-inch rectangular SS archwires (3M Surface characterization Unitek), and 100 upper canine brackets with a slot di- The surfaces of the samples were examined using mension of 0.022 inches and zero torque and tip values Dektak 8 Profilometer and Nanoscope IV Multimode (Victory series, 3M Unitek; Table 1). Atomic Force Microscopy (AFM) (Veeco Metrology Inc., Santa Barbara, CA,