Aim: To report and evaluate the confinement of metal ions released by dental amalgam restorations in vacuum-formed thermoplastic retainers (VFRs). Methods: VFR samples that contained corrosion tarnish corresponding with dental amalgam restorations were collected from patients, and replacement retainers were fabricated. The stained retainers were tested for trace metals utilizing inductively coupled plasma-atomic emission spectrometry (ICP-AES) and for mercury utilizing cold-vapor atomic absorption (CVAA). The results were compared to a control piece of VRF material from the manufacturer. Results: The tarnished sections of the VFRs contained mercury (61.00 ppm), calcium (205.00 ppm), and zinc (3.05 ppm). The control sample results were below qualitative limits for metal ion and mercury testing and can be considered, for our purposes, to be uncontaminated. Conclusion: VFRs that cover surfaces of teeth restored with dental amalgam become tarnished and confine amalgam corrosion products, including mercury and zinc. Orthodontics 2011;12:70–74.

Key words: aligners, staining, thermoplastic