Modelling of Cr and Ni ions release during orthodontic treatment: In vitro and in vivo methods

• We evaluated kinetics of Cr and Ni ions release from orthodontic appliance.
• In vitro, in vivo studies on pigs (hair) and on human (hair) were modelled.
• Results of in vivo were translated to in vitro by conversion coefficient.
• This enabled to extrapolate results of in vitro trials to in vivo conditions.

The kinetics of metal ions release from orthodontic appliances in in vitro, in in vivo on pigs, and in vivo trials on patients (where hair samples were taken) was discussed. We have evaluated (by means of ICP-OES and ISO 17025) and compared the mass of Cr and Ni ions released. Not all the metal ions released from the appliance were transferred to hair tissue. The transfer factor was expressed as coefficient ω and evaluated as: ωCrpatients 33.0%, ωCrpigs 17.2%, ωNipatients 49.8%, ωNipigs 0.553%. The kinetics was described by a power function. Coefficient ω was used to combine the models: the in vitro and in vivo on animals on the one hand and the in vitro and in vivo on human on the other, which enabled the extrapolation of in vitro and translation of the results into in vivo conditions. The dose of metal ions released during orthodontic treatment was estimated.