Surface characterization of retrieved NiTi orthodontic archwires

The structure and morphological condition of retrieved NiTi orthodontic arc hwires was evaluated and any possible alterations in the surface compositio n of the alloy following 1-6 months in vivo were characterized. NiTi wires (GAC, German Orthodontics, ORMCO) of various cross-sections were collected through a retrieval protocol and were subjected to multi-technique characte rization. Optical microscopy revealed islands of amorphous precipitants and accumulat ed microcrystalline particles. Micro MIR-FTIR investigation of the retrieve d samples demonstrated the presence of a proteinaceous biofilm, the organic constituents of which were mainly amide, alcohol, and carbonate. Scanning electron microscope and X-ray microanalysis showed that the elemental speci es precipitated on the material surface were Na, K, Cl, Ca, and P, forming NaCl, KCl, and Ca-P precipitates. Increased intra-oral exposure was consist ently associated with the presence of a mature film, while evidence of allo y delamination, pitting, and crevice corrosion, as well as a notable reduct ion in the alloy grain size was observed. Intra-oral exposure of NiTi wires alters the topography and structure of th e alloy surface through surface attack in the form of pitting or crevice co rrosion or formation of integuments. Further in vivo research is required t o resolve the implications of the described ageing pattern in the corrosion resistance of the alloy, the potential for nickel leaching, as well as bra cket-archwire friction variants.