EFEITOS CORROSIVOS ENCONTRADOS EM MATERIAIS MAGNÉTICOS EMPREGADOS EM ORTODONTIA

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The employment of magnetic alloys have allowed the criation of new options on odontological therapies, specially in orthodontics, where its utilization is already quite outspread. The innovation with the use of magnets came with the introduction of new magnetic alloys based on elements rare earth that belong to the lanthanum family as well as the samarium-cobalt (SmCo5 ) alloys and neodymium-iron-boron (Nd2Fe14b) ones magnets manufactured with the alloys mentioned above are more than 20 times stronger than the magnets of alluminium-niquel-cobalt. However the alloy of Nd2Fe14b being 3 times stronger than SmCo5, it is 240 times more susceptible to corrosion inside the mouth. In this work the structural , morphological and magnetic characterization was carried out in the magnetic alloy Nd2Fe14b for orthodontic application and also the magnetic force and magnetic fields were analysed, beyond the corrosive behavior of magnets. To simulate the buccal means and to make the corrosion tests, the 16 magnets were involved with gold and silver (by electrolytic deposition) and were immerged in a solution of 1% lactic acid for a period of 70 days; and the value of their magnetic fields checked weekly by a hall probe. The element Fe released in the acid solution was analysed weekely through the atomic absorption spectrometry. The magnetic samples corroding were submitted to microanalyses by means of SEM (Scanning electron microscopy) and EDS (energy dispersive X ray detector) in the periods of 14, 21 and 70 days (in the end of the experiments). In the final experiments they were submitted to an analysis of x-ray diffraction. Statistics test (t test and ANOVA) were applied to check the differences among the averages of magnetic fields in both magnetic groups and correlate the corrosion process on magnets with the time of the experiment respectively. The initial characterization of the material was made through the x-ray diffraction analysis, thermal analysis (TG/DTA), SEM, EDS and WDS (wave dispersive spectrometry).For the measurements of magnetic forces, magnets were applied, attractively and repulsively, an accurate scale and a device for measure heights. To carry out the measurements of magnetic field variations, some magnets were applied in an attractive configuration: one magnet was placed in a fixed vertical stick an a second magnet adapted to XY position and angular dependency. The measurements were made applying a Hall probe. The first results of the microanalysis showed a magnet composed meanly by Nd2Fe14b phase, coated in Au, Ag, Cu and Ni, in 3 layers. The forces generated by the magnets in both configurations showed compatible for generating orthodontic movement, specially in short distances and low angles among the magnets. The magnets samples of boths groups suffered corrosion evident by the increasing of Fe free and confirmed by x-ray diffraction. analyses. The formation of new phases not iron magnetic gave a decreasing in the measures of the magnetic fields. The t test showed that the differences among the decreasing averages were not significant- 0,7333 mV for gold ones and 0,6803 mV for the silver ones. A significant reduction occurred in the magnetic fields in function of the time, when the gold and silver magnets were immerged in lactic acid (F=4691, gl=9, p>0,001).There was a difference of magnets in manufacturing view point (via powder metallurgy) and/or in the coating process via electrolytic deposition. Thus, for the application of this material in buccal means, with mechanical efficiency and effective biocompatibility, it is recommended that it must be hermetically sealed.

ASSUNTO(S)

engenharias magnetos, ortodontia, corrosão, campo magnético

ACESSO AO ARTIGO

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