Exposure to metals from orthodontic appliances by hair mineral analysis

The aim of the present work was to investigate the exposure of patients to metals released from orthodontic appliances in situ. The paper reports the results of biocompatibility studies of orthodontic appliances by an in vivo method using hair sampled from the group of patients (N = 28) and a control group (N = 18). The mean content of metals (Ni, Cr, Mn, Fe) in hair that were hypothesized to be systemically absorbed from stainless steel, was provided. The highest difference between the groups was found for Ni (39% higher level in hair of patients), Mn (18%), Fe (4.1%), Cr (2.5%), as calculated by a new dimensionless metal release coefficient (α). The second coefficient defined in the present work (β) corresponded to the difference in the mean content of elements between the groups. The coefficient was the highest for Fe, subsequently Ni, Mn and Cr. None of the differences was statistically significant. For each group and a given element, ranges between 10th and 90th percentile were determined. The upper value of the range differed the mostly between the groups for Ni (82.5%) showing that stainless steel of orthodontic appliance can be the source of exposure to this element. The difference was also identified for Mn (26.5%). For Cr and Fe, the lower value of the range was elevated. It was noted that 22% of patients undergoing orthodontic treatment had elevated levels of Ni in hair. A correlation matrix between the content of the elements in hair was calculated. Statistically significant correlations were found between Cr and Fe, showing similar sources of exposure. Multiple regression analysis showed the dependence of Ni content (dependent variable) on the level of Co and Mg (synergism) and V (antagonism).