Application of a Molybdenum and Tungsten Disulfide Coating to Improve Tribological Properties of Orthodontic Archwires

Abstract

Coatings incorporating nanoparticles of molybdenum and tungsten disulfide (MoS2 and WS2)—known for their lubricating properties—are applied to orthodontic stainless steel wires to verify if there is an improvement in terms of tribological properties during the sliding of the wire along the bracket. To simulate in vitro sliding of the wire along the bracket and evaluate friction 0.019 × 0.025 inches orthodontic stainless steel (SS) wires were subjected to the application, by electrodeposition, of Ni, Ni + MoS2, and Ni + WS2. The samples produced were analyzed with scanning electron microscopy and assessment of resistance to bending. Thirty-two test conditions have been analyzed, arising from the combination of four types of coatings (SS bare wires and strings with three types of coating), two types of self-ligating bracket (Damon Q, Ormco and In-Ovation R, GAC International), two bracket-wire angles (0° and 5°), two environments (dry and wet). Analyses carried out on the samples show acceptable coatings incorporating MoS2 and WS2 and a resistance of coatings after a minimum bending. In “dry conditions” a statistically significant decrease in friction occurs for wires coated with MoS2 and WS2 if associated with the In-Ovation bracket. In “wet conditions” this decrease is observed only in isolated test conditions. Analysis of the wires after sliding tests show little wear of the applied coatings. Nanoparticles are acceptable and similar in their behavior. Improvements in terms of friction are obtained pairing coatings incorporating MoS2 and WS2 with the In-Ovation bracket in dry conditions.