In vitro corrosion of metallic orthodontic brackets: influence of artificial saliva with and without fluorides

Abstract

Objective: This in vitro study verified the resistance to corrosion of metallic brackets, evaluating the superficial aspects in scanning electron microscopy (SEM) and the residual components. Methods: The sample consisted of 17 sets of brackets of four different metallic alloys: Titanium, Cobalt-Chromium, Stainless steel with low nickel concentration and with titanium nitride coating (NiTi). Twelve sets were submitted to corrosion by immersion in 50 ml of artificial saliva (pH 6.5) and four in saliva (pH 6.5) containing fluoride (2 g/l), all at a temperature of 37 ºC and analyzed after 7, 9 and 11 weeks. One was kept as control set. The analysis consisted in qualitative evaluation of the corrosion by the images obtained on the SEM, in semiquantitative evaluation of chemical composition of the surface residue by SEM-EDS and the amount of ions released in saliva on evaluation of atomic absorption spectrophotometry. Results: The results showed that the pure titanium brackets and the ones with low nickel concentration were superior regarding resistance to corrosion. The cobalt-chromium alloy showed the greatest corrosion. In the presence of fluoride, it was observed greater variation in all alloys, especially in the ones of NiTi coated steel and the ones of cobalt-chromium. Conclusion: Although observed corrosion on the SEM, the spectrophotometry showed low ions release in the artificial saliva, however, the presence of fluoride negatively affected the corrosion resistance. Objetivo: este estudo in vitro verificou a resistência à corrosão de braquetes metálicos, avaliando-se os aspectos superficiais em microscopia eletrônica de varredura (MEV) e os componentes residuais formados. Métodos: a amostra consistiu de 17 conjuntos de braquetes de quatro diferentes ligas metálicas: titânio, cobalto-cromo, aço inoxidável com baixa concentração de níquel e com cobertura de nitreto de titânio (TiN). Doze conjuntos foram submetidos à corrosão por imersão em 50ml de saliva artificial (pH 6,5) e 4 em saliva (pH 6,5) contendo flúor (2g/l), todos sob temperatura de 37ºC, e analisados após 7, 9 e 11 semanas. Uma montagem foi mantida como controle. As análises consistiram na avaliação qualitativa da corrosão por meio das imagens obtidas no MEV, na avaliação semiquantitativa da composição química dos resíduos superficiais por meio de MEV-EDS e da quantidade de íons liberados nas salivas na avaliação da espectrofotometria de absorção atômica. Resultados: os resultados demonstraram que os braquetes com liga de titânio puro e os de aço com baixa concentração de níquel foram superiores em relação à resistência à corrosão. A liga de cobalto-cromo foi a que apresentou maior corrosão. Na presença do flúor, observaram-se maiores alterações em todas as ligas, com destaque para as de aço cobertos com TiN e as de cobalto-cromo. Conclusão: apesar de se observar a corrosão no MEV, a espectrofotometria mostrou baixo desprendimento de íons nas salivas artificiais, porém a presença do flúor interferiu negativamente na resistência à corrosão.Palavras...

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