Effect of manufacturing method on metal ion release from orthodontic brackets and tubes

The aim was to evaluate ion release from various brackets and tubes, considering manufacturing methods and alloy composition. An experimental in vitro study was conducted following UNE-EN ISO 10,271:2020 and ISO 27,020 standards. The sample included 120 brackets and 32 tubes, divided into: Group 1 (control solution), Group 2 (MIM brackets), Group 3 (CAD-CAM brackets with welded mesh), Group 4 (CAD-CAM monoblock brackets), Group 5 (MIM tubes), and Group 6 (CAD-CAM tubes). Two sets per bracket and tube type were tested, with triplicate measurements per sample. Devices were immersed in a lactic acid and NaCl solution (pH 2.34) for 7 days at 37 °C. Ion release (Ni, Cr, Cu, Mo, Mn, Si) was quantified using inductively coupled plasma optical emission spectrometry (ICP-AES). Statistical analysis included Kruskal-Wallis and post hoc tests (p < 0.05). Significant differences were found in ion release among bracket types. Group 2 (MIM) showed the highest Ni release (mean ± SD: 2.59 ± 0.35 µg/ml), Cr (7.05 ± 0.73 µg/ml), and Cu (2.35 ± 0.28 µg/ml), with p < 0.001. CAD-CAM monoblock brackets (Group 4) exhibited the lowest levels across all elements. No significant differences were observed between tube groups and the control (p > 0.05). As a conclusion, orthodontic devices release trace metal ions, with CAD-CAM monoblock brackets showing superior corrosion resistance.