DO ESTHETICS CONTRADICT WITH FUNCTION? IN VITRO ASSESSMENT OF LOAD DEFLECTION AND FRICTIONAL RESISTANCE OF COATED VERSUS UNCOATED SUPERELASTIC NICKEL-TITANIUM ARCHWIRES

Abstract

Objectives: The present study aimed to investigate the effect of esthetic coating on the load deflection properties, surface roughness and frictional resistance of superelastic Ni-Ti orthodontic wires. Materials and Methods: Four types of Ni-Ti wires were investigated: Alpha Wire Super Elastic Ni-Ti, OrthoPro (Uncoated OP) and its coated counterpart: Alpha Wire Tooth-Coated Super Elastic Ni-Ti, OrthoPro (Coated OP); Super-elastic Nitanium, Ortho Organizer (Uncoated OO) and its coated counterpart: Super-elastic Nitanium Tooth Tone, Orthodontic Organizer (Coated OO). The load deflection properties were investigated using three-point elastic bending test by a universal testing machine (Lloyd Instrument LR5K series, London, UK) to record the average unloading force (n=8). The surface roughness was measured using a non-contact profilometer (ZYGO Maxim-GP 200, USA) (n=4). The static and dynamic frictional resistances were measured using a specially designed test assembly that allows sliding the wires through the slots of monocrystalline zirconia brackets using a universal testing machine (n=8). Results: No significant difference was found between the coated OP wires and their uncoated controls regarding the load deflection, surface roughness or frictional resistance whether static or dynamic. On the contrary, compared to their uncoated group, the coated OO wires showed significantly lower average unloading force, higher surface roughness, and higher static and dynamic friction. Conclusions: The effects of the esthetic coating on the critical function-related properties of orthodontic wires vary from one manufacturer to another which indicates that satisfying the esthetic demand does not always come at the expense of wire function.