I believe the worry with conventional mercury/amalgam fillings is that the mercury continues to exude minor quantities of mercury vapour which is poisonous to the brain above. I have a variety of fillings and a few crowns, but most recent fillings are buildups with epoxy resin using a blue laser to set each level of the fill. They set almost immediately, no problems with vapour, are very strong indeed, but, of course, are more expensive. A very good solution!