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Coating failure of commercial orthodontic magnets and DNA fragmentation of oral mucosa cells.

OBJECTIVE
To investigate possible adverse effects of orthodontic magnets on the oral mucosa.


METHODS
Twenty orthodontic patients, between 14 and 20 years of age, were used. All patients consented to participate in the trial, which ran for six months. Following extraction of the first premolars, samarium-cobalt (SmCo5) orthodontic magnets were used to move the upper right canines into the extraction spaces. The contralateral canines were retracted with elastomeric chain. The orthodontic appliance consisted of direct-bonded standard edgewise fibreglass brackets and molar tubes, and teflon-coated preformed archwires. At regular scheduled visits the following were recorded: the condition of the protective magnet coating; weight loss by the magnets; levels of nickel, iron and chromium ions in unstimulated saliva; viability of recovered oral mucosa cells with trypan blue. DNA fragmentation of the oral mucosa cells was analysed at the start of the trial, after one week, one month, three months and six months with the single cell gel electrophoresis assay (Comet assay). The elemental compositions of five magnets were assessed with energy dispersive X-ray microanalysis.


RESULTS
By the third month the magnets had lost their protective resin coats. At six months the magnets had lost 3 per cent of their initial weights. Significant weight loss and raised saliva levels of nickel, iron and chromium ions occurred from the first week. The number of oral mucosa cells with DNA fragmentation increased steadily on both sides of the mouth from the first week. More DNA fragmented cells occurred on the Magnet side than on the Non-magnet side. The trial was discontinued when half of the subjects showed DNA damaged mucosal cells.


CONCLUSIONS
Because the protective coating failed after a few weeks, orthodontic magnets are unsuitable for long-term intra-oral use. It is uncertain if the greater cell damage on the Magnet side was due to the corrosion products, proximity to the static magnetic field or both factors.