THE CORROSION RESISTANCE AND CYTOTOXICITY OF A COMMERCIAL Nd-Fe-B MAGNET IN SIMULATED PHYSIOLOGICAL SOLUTION Mara Cristina Lopes de Oliveira Instituto de Pesquisas Energéticas e Nucleares (CCTM) Av. Prof. Lineu Prestes, 2242, CEP 05508-900, São Paulo-SP, Brasil Email: mcolivei@net.ipen.br Sizue Ota Rogero, Instituto de Pesquisas Energéticas e Nucleares (CQMA) Av. Prof. Lineu Prestes, 2242, CEP 05508-900, São Paulo-SP, Brasil Email: sorogero@net.ipen.br Mitiko Saiki Instituto de Pesquisas Energéticas e Nucleares (CRN) Av. Prof. Lineu Prestes, 2242, CEP 05508-900, São Paulo-SP, Brasil Email: mitiko@curiango.ipen.br Isolda Costa Instituto de Pesquisas Energéticas e Nucleares (CCTM) Av. Prof. Lineu Prestes, 2242, CEP 05508-900, São Paulo-SP, Brasil Email: icosta@net.ipen.br Abstract. In this investigation, in vitro corrosion tests have been carried out in naturally aerated Hank’s solution at 25 o C, to evaluate the corrosion resistance of a commercial sintered NdFeB magnet by immersion test and electrochemical techniques. Generalized corrosion occurred and Instrumental Neutron Activation Analysis (INAA) was applied to analyze elements leached into Hank´s solution. The results showed that Co, Fe and Nd have been released into the physiological medium. In the cytotoxicity test by neutral red uptake and agar diffusion methods, the commercial Nd- Fe-B magnet tested did not present toxicity. Keywords. Corrosion, Biomaterials, Cytotoxicity, Sintered Magnets, Nd-Fe-B. 1. Introduction Magnets have been used in dentistry since the 1950’s to improve retention and stability of dental prostheses (Freedman, 1953). In the past, however, the large size required to produce adequate forces limited their extensive use (Moghadam and Scandrett, 1979; Behrman, 1964; Javid, 1971; Wilson et all, 1999). Since the introduction of Rare Earth magnets it has become possible to produce magnets with small enough dimensions to be used in dental applications as retentive devices for overdentures, mainly due to their strong force and compactness (Becker, 1970; Sagawa et all, 1984; Tsutsui et all, 1979). These magnets show great improvements in the maximum energy product comparatively to the old types, leading to a huge reduction in the size required to generate a particular magnetic flux (Harris, 1990). Dental materials should present high corrosion resistance and be innocuous to human tissues, however, Nd-Fe-B magnets are highly susceptible to corrosion. One of the main problems associated with the use of Rare Earth-Fe-B magnets in clinical use is corrosion once these types of magnets have low corrosion resistance in aqueous media. For dental applications they are usually encapsulated in a stainless steel or titanium can. However, due to wear of the can or failure of the laser weld, saliva is able to leak into the can and cause corrosion of the magnet. Therefore, there is a continuing concern on investigating the potentially harmful biological effects caused by toxic elements released from the magnet due to corrosion. In this study, the corrosion resistance of a commercial sintered Nd-Fe-B magnet in Hank’s solution has been investigated by electrochemical impedance spectroscopy and potentiodynamic polarization curves. The toxicity of magnetized and demagnetized Nd-Fe-B magnet was also investigated in the neutral red uptake and agar diffusion cytotoxicity assays. The corrosion products leached into Hank’s solution were analyzed by instrumental neutron activation analysis (INAA).