A Novel Friction-Reduced Orthodontic Archwire Coated with Fulleren-like Nanoparticles

Objectives: Sliding a tooth along an archwire involves a frictional type of force that resists this movement. Use of excessive orthodontic force might cause loss of anchorage and root resorption. This study was aimed at reducing this friction by coating the orthodontic wire with inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS₂), which are known for their excellent dry lubrication properties. Methods: The first part of this study dealt with coating the orthodontic wires. The IF-WS₂ were dispersed in an aqueous solution of nickel phosphorus (Ni-P) and plated on the wire by means of electroless deposition. Analysis of the microstructure was conducted with scanning electron microscopy and energy-dispersive X ray spectrometry. The adhesion of the coating to the wire was evaluated by scotch bond and bend tests. After achieving a coating with adequate properties, tribological tests were conducted using the “ball on flat” method and a 50% reduction in the coefficient of friction on the coated wires was recorded. Next, we evaluated friction that develops between the wire and bracket in a setup simulating the type of movement encountered during tooth movement. Coated and uncoated stainless steel wires were engaged into brackets, which were attached to a special device set at 0°, 5° and 10° angulations to the wire. The device was connected to the base of an instron-4502 testing machine and pulled down at a constant speed of 10 mm/min to a distance of 5mm. Results: The friction forces were reduced on the coated wire by up to 54% (from 4.00N±0.19 on the uncoated wire to 1.85N±0.21 on the coated one) at the 10° angulation. Conclusions: Coating archwires with a composite Ni P-IF-WS₂ will be able to offer a novel opportunity to substantially reduce friction force during orthodontic tooth movement after further investigating the biocompatible properties of the coating.