Fe leaking from orthodontic appliances affects buccal enamel more than lingual during in vitro experiment

The presence of trace metals in the oral cavity, whether natural or treatment-induced, may influence enamel properties and health. Evidence suggests that metals released from orthodontic appliances affect enamel integrity, though the underlying mechanisms remain unclear. This study examined whether Fe ions from orthodontic devices preferentially incorporate into either the buccal or lingual enamel. For this, six human molars underwent a 12-month in vitro simulation involving metal appliances and cyclic pH fluctuations. Bacterial and enzymatic effects were not assessed. Lingual-buccal enamel cross-sections were analysed using LA-ICP-MS pre- and post-experiment. Fe concentration increased over time, varying among teeth. Fe accumulated significantly more (Student's t-test, p = 0.000000) and penetrated deeper (U-Mann-Whitney, p = 0.000000) on the buccal side. Unlike the lingual side, the buccal Fe increase correlated with a Ca decrease (Pearson, r > -0.79), while final Fe levels correlated with initial Zn on both sides (r > 0.68). Findings suggest greater Fe susceptibility in buccal enamel with an assimilation mechanism different from lingual enamel. Further research should examine its and Zn's roles in post-treatment alterations, with proposed clinical trial outlines. The in vitro method used may help optimise buccal and lingual systems for enamel preservation and post-appliance care.