engleski

Chemical stability of nickel-titanium (NiTi) orthodontic wire in artificial saliva and commercial fluoride agents

AIM: Determination of corrosion rate of NiTi orthodontic wires in artificial saliva and commercial fluoride agents in imitation of regular prophylactic regime. MATERIALS AND METHODS: Ten cm long specimen of NiTi wire was immersed in 10 mL of artificial saliva (1.5 g/L KCl, 1.5 g/L NaHCO3, 0.5 g/L, NaH2PO4–H2O, 0.5 g/L KSCN, 0.9 g/L lactic acid, pH=4.8) incubated at 37 °C. All experiments were performed in triplicate. Artificial saliva samples were collected after 3, 7, 14, 21, and 28 days of immersion and the amount of eluted Ni2+ and Ti4+ ions were measured by means of inductively coupled plasma-optical emission spectroscopy. In between collection of saliva, wires were immersed for 5 minutes at 37 °C to three commercial fluoride agents as imitation of regular weekly treatment: 1) Elmex gelée (7500/5000 ppm of fluoride) ; 2) MI Paste Plus (900 ppm of fluoride) ; 3) Mirafluor-k-gel (6150 ppm of fluoride). After fluoridation, the wires were rinsed with distilled water and immersed to fresh artificial saliva. One experimental group was immersed only to artificial saliva. The fluoride agents were chosen because of their commercial availability, identical methods of application, various fluoride ion concentrations, various chemical formulations, and different pH values (Mirafluor-k-gel 5.1 ; Elmex gelée 5.5 ; MI Paste Plus 6.6). RESULTS: Release of Ni2+ and Ti4+ ions from NiTi orthodontic wires increased in following order: artificial saliva < MiPaste < Elmex < Mirafluor. Calculated average daily Ni2+ ion release did not reach allergenic potential. CONCLUSIONS: Chemical stability of NiTi wires decreases with increased fluoride concentrations due to deterioration of protective TiO2 layer.

corrosion; ICP-OES; NiTi wires; prophylactic agents

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