Metal ion release from fixed orthodontic appliances--an in vivo study

The aim of this study was to test the hypothesis that there is no difference in salivary metal ion content between subjects with fixed orthodontic appliances and their same-gender sister or brother without any orthodontic appliance. This retrospective study was carried out on 28 subjects (16 females and 12 males) who had undergone fixed orthodontic therapy for a duration of 12-18 months. In order to limit the effects of dietary and hygiene habits on salivary metal ion concentration, a same-gender brother or sister (total of 28 subjects) was selected as a control. Approximately 5 ml of saliva was collected from each subject, and the samples were analysed using an atomic absorption spectrophotometer. The detection limit of the method for sample solutions was 1 ng/ml. Since some variables were not normally distributed, non-parametric tests (Mann-Whitney U and Wilcoxon W) were used for statistical analysis. The mean salivary nickel (Ni) content in subjects with and without a fixed orthodontic appliance was 18.5 ± 13.1 and 11.9 ± 11.4 ng/ml, respectively. A statistically significant difference (P < 0.035) was found between the two groups. The mean salivary chromium (Cr) ion level recorded was 2.6 ± 1.6 ng/ml in the study group and 2.2 ± 1.6 ng/ml in the control group. The difference, however, was statistically insignificant. Within the limits of this in vivo study, it can be concluded that the presence of fixed orthodontic appliances leads to an increased concentration of metal ions in salivary secretions.