There are a tremendous different types of white fillings and cementing agents. I learned about that after speaking with my naturopath and dentist. You have to find a competent dentist - one that does this all the time - one that has good experience with it. It's also unfortunate if one has a dentist that may do too much work, when it may not be necessary.
It's necessary to do some research on this, before deciding. Things are much different now, than what they were, from what I've read. Advertisements claim that the white fillings are much better than what they used to be. I don't know for sure, but that's what they say....
Sorry to hear of anyone's troubles with this. My dentist and I decided that I would have the change-over for cosmetic reasons. I didn't want him to get caught up in the controversy. It was my decision alone to have the mercury removed from my mouth. It wasn't until years later, when I continually got better, that I realized further how fortunate I was to have these toxins removed.
To each his own, but I won't have mercury in my mouth at any cost. I used to be so sick that it hurt to walk. Now I run for miles.
I can't understand how someone can mess up with white fillings so bad. All my dentist did, was remove the poisonous dental amalgam (also he took precautions with a dental dam etc.) and then he filled the newly-made cavity with a temporary plug. We waited until the shop made the white filling piece from the mold, and he cemented it in. It has the same shape as my original tooth. There's no extra filling, gaps, cracks, or anything bad. These fit just like a glove. I can barely see that they are there - only with a flashlight (or as the British say - with a torch).
To sum it up: Find a good dentist - one that will listen to you - one that communicates very well - one that is technically knowledgeable.