The aim of this thesis was to explore the extent of metal ion release in corrosive media, to assess in vitro the cytotoxicity of these appliances, and to investigate whether an existent alternative, can sufficiently replace the standard metallic wire used for orthodontic retention.
The main conclusions were: 1. "Nickel-free" orthodontic retention wires are not free of release of Ni; pH and mechanical loading influence the release of nickel from the wires tested. For the Pd-alloys casting manipulation to shape a crown and surface polishing, determined the release of metal ions. 2. The cumulative effect of the continuous release of ions from alloys for oral application may contribute to cellular damage. Concentrations of metallic salts equivalent to those reported to be released from dental alloys were able to induce cellular toxicity, although the appliance is not considered cytotoxic and, as such, safe for clinical application. 3. Fiber-reinforced composite retainers are not reliable alternatives for (long-term) orthodontic retention. The deflection of the retainer is of prime importance to accompany physiologic teeth movement and as such prevent relapse. But, the length of "free wire", i.e. the amount of wire not covered with composite, is the most critical factor for the success of the retainer system.
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