Biocompatibility Investigation of Nickel-Titanium Archwires with New Nanocoating

Objectives: Biocompatibility is interpreted as the material’s ability to act with the appropriate response of the host in a particular situation. The biocompatibility refers not only to the degree of cytotoxicity, but also to the material’s ability to achieve the desired biological effects after its implementation. Biocompatibility of orthodontic materials is of great importance precisely because of their long-term contact with oral tissues, potential corrosion and the release of various toxic elements due to frequent pH changes in the oral cavity. The aim of this study was to investigate the biocompatibility of nickel-titanium archwires with new nanocoating using human gingival cells in comparison with nickel-titanium and stainless steel archwires.
Methods: The nanocoating consiting of TiO₂, TiN, TiN+Cu was obtained by pulsed magnetron sputtering using the commercially available nickel-titanium archwires. The samples were analized using X-ray diffraction and atomic force microscopy. The release of Ni, Ti, Cu, Fe, Cr, Zn ions into DMEM and acidic solution was conducted using ICP-OES. Biocompatibility of samples' eluates (7-day, 21-day and 28-day; n=10) was investigated using Neutral red and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide test.
Results: The nanocoating mainly consisted of an amorphous and crystal phases of anatase and rutile. The release of nickel was statistically lower in case of nanocoated archwires both in DMEM and acidic environment (p<0.05). Only the release of zinc was statistically lower in the acidic environment for all the investigated groups compared to DMEM, as the copper for the nanocoated archwires (p<0.05). The relative cell viability was the highest regarding the 7-day eluates of nanocoated archwires (p<0.05). The metabolic activity of cells decreased following the extraction time, except in case of stainless steel archwires after 21-day (p<0.05).
Conclusions: As new nanocoated archwires showed better stability in both acidic and non-acidic conditions, as well as satisfactory biocompatibility, they may be considered for further clinical investigations.