Differences in human gingival and dermal fibroblasts may contribute to oral-induced tolerance against nickel

The prevalence of allergic contact dermatitis has increased steadily with nickel (Ni) still as the main sensitizer.1,2 In this context, it seems contradictory that orthodontic materials contain high amounts of Ni, which lead to the inevitable release of Ni ions (Ni2+) into the oral cavity.3 However, intraoral allergic reactions are rare and current evidence indicates that orthodontic treatment before piercings may even prevent Ni hypersensitivity probably via oral-induced tolerance against Ni.4 The detailed mechanisms still remain unclear.