Corrosion resistance of Ni-Cr alloys in different mouthwashes

Varias ligas tem sido utilizadas na confeccao de restauracoes proteticas nos ultimos anos. Essas ligas apresentam na sua composicao ouro, paladio, prata, niquel, cobalto, cromo e titânio; quando na cavidade bucal sao passiveis de corrosao, a qual pode empobrecer a estetica e comprometer as propriedades fisicas e biologicas. O objetivo deste trabalho foi avaliar a resistencia a corrosao de duas ligas odontologicas, Ni-Cr e Ni-Cr-Ti em tres tipos de colutorios bucais com diferentes ingredientes ativos: colutorio I u 0.5g/l de cloreto de cetilpiridineo +0.05 de fluoreto de sodio; colutorio II -0.05 de fluoreto de sodio + 0.03% de triclosan e colutorio III u 0.12% de diclonato de clorexidina. Curvas potenciodinâmicas foram realizadas por meio de potenciostato PAR283 e celula de vidro convencional de parede dupla para termostatizacao. Utilizou-se eletrodo de referencia Ag/ AgCl, KClsat e auxiliar espiral de platina. A microestrutura das duas ligas foi observada por meio de microscopia otica. Analise das curvas obtidas mostraram que a liga Ni-Cr foi menos reativa na presenca de digluconato de clorexida a 0.12%, enquanto a liga Ni-Cr-Ti foi mais sensivel para os outros dois tipos de colutorio. Isto ocorreu, provavelmente, devido a presenca de titânio na composicao desta liga. Analise microestrutural revelou microsestrutura dendritica na liga Ni-Cr e euteticos na liga Ni-Cr-Ti(AU) Several alloys have been used for prosthodontics restorations in the last years. These alloys have a number of metals that include gold, palladium, silver, nickel, cobalt, chromium and titanium and they are used in oral cavity undergo several corrosion. Corrosion can lead to poor esthetics, compromise of physical properties, or increased biological irritation. The objective of this study was evaluated corrosion resistance of two alloys Ni-Cr and Ni-Cr-Ti in three types of mouthwashes with different active ingredients: 0.5g/l cetylpyridinium chloride + 0.05% sodium fluoride, 0.05% sodium fluoride + 0.03% triclosan (with fluor) and 0.12% chlorohexidine digluconate. The potentiodynamic curves were performed by means of an EG&G PAR 283 potentiostat/galvanostat. The counter electrode was a platinum wire and reference electrode was an Ag/AgCl, KCl saturated. Before each experiment, working electrodes were mechanically polished with 600 and 1200 grade papers, rinsed with distilled water and dried in air. All experiments were carried out at 37.0oC in conventional three-compartment double wall glass cell containing mouthwashes. The microstructures of two alloys were observed in optical microscopy. Analysis of curves showed that Ni-Cr alloy was less reactive in the presence of 0.12% chlorohexidine digluconate while Ni-Cr-Ti alloy was more sensitive for others two types of mouthwashes (0.5g/l cetylpyridinium chloride + 0.05% sodium fluorideri and 0.05% sodium fluoride + 0.03% triclosan). This occurred probably due presence of titanium in this alloy. Microstructural analysis reveals the presence of dendritic and eutectic microstructures for NiCr and Ni-Cr-Ti, respectively(AU)