Metallic Orthodontic Materials Induce Gene Expression and Protein Synthesis of Metallothioneins

Due to the long-term contact with metallic elements of orthodontic appliances, the potential influence of released metal ions on living organisms and the type of induced changes was investigated.

Twenty-four young domestic pigs classified in two groups (experimental and control) were chosen as the object of this study. In the experimental group of animals, two metal plates consisting of orthodontic bands representing the mass of orthodontic appliance were mounted on the internal side of the cheek for six months. The liver, lung, and brain samples were taken post mortem from animals of both groups. The gene expression of two isoforms of metallothionein (MT-1 and MT-2) were investigated using the qPCR technique. Protein expression was confirmed by the Western blot and ELISA techniques.

The differences in metallothionein concentrations were observed in the lung and brain in the group of experimental animals, but not in the liver. The expression of MT-1 and MT-2 genes in the experimental vs. control group (respectively) was as follows: lung MT-1 1.04 vs. 1.11, MT-2 0.96 vs. 1.05, liver MT-1 0.89 vs. 0.91 vs. 1.12, MT-2 0.91 vs. 1.05, brain MT-1 1.24 vs. 1.20, and MT-2 0.955 vs. 0.945. These results were confirmed by gene activity, which was tested by qPCR. This increased the activity of metallothionein genes in the lungs and brain as a consequence of the release of metal ions into these tissues. The possible effects of detected change in metallothionein-2 gene expression could be the alteration of physiological functions of lung tissue.

The effect of long-term exposure to metal orthodontic appliances on metallothioneins gene expression, as well as the induction of protein synthesis was proved.