We thank Dr Zahrowski for his interest in our article. The term “toxic ions” was originally based on the basic characterization of the metal components of silver solder, since all belong to the group of heavy metals—defined as metals with medium to high atomic numbers and that are toxic in low concentrations. Moreover, metals are chemically reactive and highly bioaccumulative; ie, living organisms cannot eliminate them.
Allied to this, studies in the literature show that these ions (copper, zinc, cadmium, and silver) are considered potentially hazardous, and are included in the list of substances and processes considered to have a high risk to human life by various regulatory bodies, such as International Register of Potentially Toxic Chemicals of the United Nations Environment Program, the World Health Organization International Agency for Research on Cancer, and the United States National Toxicology Program. We also add that, given the results in the literature on the cytotoxicity of silver solder, high toxicity was observed, confirming the correct use of the term.
According to Barrett et al, when assessing the potential influences of orthodontic appliances on health, one must measure 3 factors: the rate of release of harmful components from metal appliances in the oral cavity, the degree of absorption of metal compounds by the body, and the time that these compounds are retained in the tissues. They added that the release of ions from orthodontic appliances might increase the concentration of ions in the body, above the concentration of intake of or exposure to metals in the environment.
These findings underlie our concern with the results, since, even with a low concentration of ions, there could be an association with other sources of contamination favoring the retention or absorption by the body, and this could lead to clinical signs and symptoms. Along this line, the concentrations cited as the threshold maximum intake per day apply only to the risk of acute toxicity, underestimating the ability of ions to cause subclinical or chronic changes, whose effects are expressed in the long term and are not clear in the literature.
Another important detail is that there are reports of greater susceptibility to toxicity in children (stage at which some treatment is performed with orthodontic appliances) and elderly people. The primary means of exposure in children to many toxic metals is food, and they consume more calories per total weight than do adults. In addition, children have higher rates of gastrointestinal absorption of metals. The rapid growth and cell division in the body of a child represent opportunities for the effects of toxicity.
Finally, in the last paragraph of our article, we suggested the need for longer-term studies, as well as research into blood and urine levels to check for possible retention and absorption of these ions by the human body and their possible consequences.