Dr. Popat talks about amalgam fillings
According to scientific research amalgam fillings, which contain Mercury, are safe. They are, as a rule, safe for a few reasons:
When there are large amalgam fillings present there is the danger of these fillings cracking when hot or cold food or drinks are consumed. As the different metals involved have a different rate of expansion or contraction, when heated or cooled, there is the danger of the filling starting to separate from the tooth, or of the compound itself slowly breaking down.
The problem of large amalgam fillings has another, perhaps an even greater risk by forcing the tooth itself to crack. Large amalgam fillings can do this because the tooth has been excavated severely and, as such, it is already weakened to the point that a small amount of pressure can crack the tooth.
Because large amalgam fillings have multiple problems it is wise to have these teeth checked by your dentist and to be consulted about other choices. Gold restorations are always a wise choice as gold expands and contracts very nearly the same as the natural components of a tooth.
Other beneficial properties of gold restorations include the malleability and the strength of gold fillings which also match very closely to that of your natural teeth. The cost of creating gold castings in a lab with the molds from your dentist are quite high, but the long term benefits may out way the up front costs. You will need to ask your dentist about the cost and benefits of gold restorations.
There is a lot of controversy, in general, about the safety of amalgam fillings. To acquire a broader view of whatever risks that may be involved and to learn more about the fear factor, that seems to get the most attention, you will find it useful to visit Quackwatch by Stephen Barrett, M.D. as it is an informative site on these matters, as well as for many other topics.