We dont need a placebo group randomly assigned to receive fillings without hg. We know that hg is toxic. The only issue is whether the level of hg exposure from fillings is within a toxic range. There is conclsive evidence that Amalgam hg exposure exceeds levels considered safe by govt. agencies.
There are however studies on sheep and monkeys which are double blind.
Dentists are'nt scientists. Most people go to dental school because they are'nt smart enough to get into a U.S. med school.