Characterization of the coatings covering esthetic orthodontic archwires and their influence on the bending and frictional properties

Objective: To analyze the coatings covering esthetic orthodontic wires and the influence of such coatings on bending and frictional properties. Materials and Methods: Four commercially available, coated esthetic archwires were evaluated for their cross-sectional dimensions, surface roughness (Ra), nanomechanical properties (nanohardness, nanoelastic modulus), three-point bending, and static frictional force. Matched, noncoated control wires were also assessed. Results: One of the coated wires had a similar inner core dimension and elasticity compared to the noncoated control wire, and no significant differences between their static frictional forces were observed. The other coated wires had significantly smaller inner cores and lower elasticity compared to the noncoated wires, and one of them showed less static frictional force than the noncoated wire, while the other two coated wires had greater static frictional force compared to their noncoated controls. The dimension and elastic modulus of the inner cores were positively correlated (r=0.640), as were frictional force and total cross-sectional (r=0.761) or inner core (r=0.709) dimension, elastic modulus (r=0.777), nanohardness (r=0.802), and nanoelastic modulus (r=0.926). The external surfaces of the coated wires were rougher than those of their matched controls, and the Ra and frictional force were negatively correlated (r=-0.333). Conclusions: Orthodontic coated wires with small inner alloy cores withstand less force than expected and may be unsuitable for establishing sufficient tooth movement. The frictional force of coated wires is influenced by total cross-section diameter, inner core diameter, nanohardness, nanoelastic modulus, and elastic modulus. (Angle Orthod. 2017;87:610-617).