Application of zirconium-coated titanium wires as restorative orthodontic materials

Abstract

Orthodontic archwires are made from different alloys. It is now possible to match phases of treatment with orthodontic archwires according to its mechanical properties. On this basis, the titanium molybdenum alloys (TMA) in its beta phase have an excellent combination of strength and flexibility when used as archwires to apply biomechanical forces that affect tooth movement. It has recently gained increased popularity in orthodontic treatment. There are, however, disadvantages associated with the use of orthodontic archwires, such as high surface roughness, which increases friction at the archwire-brackets interface during the sliding process. The surface roughness of dental materials is of utmost importance. Properties such as desirable tensile strengths, load deflection, hardness and low modulus of elasticity and resistance against corrosion & wear determine the area of the contact surface, thereby influencing the friction. The main object of this study was to improve the strength and surface roughness of the beta-titanium orthodontic archwires (β-Ti III) and timolium archwires (TIM), taking into account of retention of the archwires strength. The following tasks were performed. Layers of Zr were deposited on the β-Ti archwires and compared with the archwire strength before and after Zr deposition. The structure of selected archwires and its composition and surface roughness was investigated before and after Zr deposition, using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The force of selected archwires before and after deposition with layers of Zr by Hounsfield deflection testing was studied. Two commercially available orthodontic archwires were used in this study, namely, β-Ti III and TIM orthodontic archwires. The archwires were cut into 25 mm long specimens. In this study, the electron beam-physical vapour deposition (EB-PVD) technique was applied to deposit pure Zr (thicknesses of 5, 10, 25 and 50 nm) on selected archwires and the effects thereof were investigated using AFM, SEM and the Hounsfield deflection test. Results of SEM and AFM analysis and deflection tests showed significant differences between Zr-coated archwires compared with uncoated archwires. Zr-coated archwires (5, 10, 25 and 50 nm depositions) had reduced surface roughness compared with uncoated archwires. A high load deflection rate was exhibited by the coated β-Ti III archwires and a low load deflection rate was exhibited by the coated TIM archwires. There was a difference in load deflection rate between the coated and uncoated archwires. Deposition of 5, 10, 25 and 50 nm Zr on both types of β-Ti orthodontic archwires is recommended for even sliding mechanics due to resulting reduced surface roughness with a good load deflection rate compared with uncoated β-Ti orthodontic archwires.

KEYWORDS Surface roughness Zirconium Titanium Deflection test Beta titanium orthodontic archwires Orthodontic archwires alloys Coated materials Electron beam-physical vapour deposition Scanning electron microscopy Atomic force microscopy