Salivary levels of nickel, chromium, iron, and copper in patients treated with metal or esthetic fixed orthodontic appliances: A retrospective cohort study

The purpose of this retrospective cohort study was to measure the salivary levels of nickel (Ni), chromium (Cr), iron (Fe) and copper (Cu) released from metal and esthetic fixed orthodontic appliances. Ninety patients were divided into three groups (n = 30): control (those who had never undergone orthodontic treatment), metal appliance (stainless steel brackets and bands, and nitinol archwires) and esthetic appliance (polycarbonate brackets and tubes, and rhodium-coated nitinol archwires). Patients undergoing orthodontic treatment had used their appliances for periods between one and six months. Ni, Cr, Fe and Cu salivary concentrations were measured by the Total Reflection X-Ray Fluorescence technique. Kruskal-Wallis and Bonferroni-Dunn test showed that Ni (p = 0.027) and Cr (p = 0.040) concentrations were significantly higher for patients undergoing metallic orthodontic treatment than for the esthetic group. No significant difference regarding Ni and Cr (p = 0.447) concentrations were observed between the metal and the control groups (p = 0.464 and p = 0.447, respectively) or between the esthetic and the control groups (p = 0.698 and p = 0.912, respectively). Ni and Cr concentrations were significantly influenced by the type of appliance used. Fe and Cu concentrations were not affected by the type or use of orthodontic appliances.