Certainly, metal fillings corrode in time and enter the circulation. They are highly toxic for the body and it is a very good idea to replace them with glass/plastic fillings, especially if they are older than 6-8 years. If have written about this subject in my book, the Key to Health and Rejuvenation, if you want more information.
When you have them replaced, you may want to do the kidney cleanse for a few days before and after the procedure to make sure any dispersed metals will be removed and not end up in the kidneys. Another method is to place Kinotakara pads under the soles of the feet while you sleep (search for this product on the web, you may use my distributor ID 900003034 if necessary). They draw metals and other toxins out of the body.
The Higgins protocol is excellent, although I believe that it is not necessary to take all those things recommended. I have had hundreds of people who safely had their metal fillings removed without any side-effects. Of course, they were all doing liver cleanses and kidney cleanses, which helped enormously.
With kind regards