In their investigation of chemical exposure in dental personnel, Lindbohm et al1 conclude by saying that there is a weak association between exposure to chemical agents and an increased frequency of spontaneous abortion. Based on their data, the authors propose in the Policy implications section that “In general, there is no need to restrict work in dental clinics during pregnancy”. We would like to express our concerns about their statement before these results reach public health policy.

In this survey, the most important methodological limitation was the complete absence of measures of exposure to chemical agents in the dental office. For example, there were neither environmental nor biological monitoring data to show the level of exposure to mercury vapor, to estimate the risk for dental staff.

Furthermore, the number of total dental amalgams was determined by a self-report questionnaire. It seems highly unlikely that all participants were able to report their exact number of mercury fillings. Self-report can lead to flawed data. We believe that the self-reported figure of amalgams cannot be considered a reliable measure of exposure to non-occupational mercury vapor.

Most unexpectedly, in their discussion, the authors did not take into account the very high concentrations of mercury vapor in the air in the breathing zone of the dental team, especially during amalgam removal.

These concentrations are often higher (10 times) than the short-term threshold limit (STEL) of 150 μg/m³, with levels peaking around 1.5 mg/m³.2 3 Consistent with this finding, dental workers show elevated placenta concentrations of mercury as well as in fetal membrane.4 Also, results from animal models suggest that chronic mercury exposure causes fetal resorption in pregnant rats.4

Surprisingly, the authors do not mention that the fetus is exposed through the placenta to mercury vapor inhaled in the operator’s breathing zone. As estimated from previous studies, the developing brain has a critical sensitivity to mercury vapor, which may cause an accumulation in fetal brain.4^–7 In addition, there is evidence that a fetus exposed to chemicals may experience adverse health effects that continue into old age.8

It has been shown in experimental study in non-human primates and humans that urine may not reflect the levels of mercury body burden.5 9 Notably, the frequency of symptoms associated with mercury vapor exposure was also increased in subjects who had low mercury concentrations compared with subjects with higher urine mercury levels.9 Our ongoing study seems to confirm this findings.10 Because of these limitations, we believe that this work is incomplete at the least.

Given that during amalgam removal dental personnel may be exposed to very high levels of mercury vapor, these unsafe procedures that put dental personnel at risk should be avoided during pregnancy.