I'm not Hellth, but I'll venture a reply to your question. When one starts mobilizing heavy metals from the body, the mobilizer, in this case, ALA, will try to mobilize whatever metal is present in the body. So it will pull metals right out of your Amalgams and they will get into your system and toxify you even more. The second go round with a toxin is much more toxic than the first and to be avoided at all costs.
It's always advisable to have all Amalgams removed before starting metal detox so as not to re toxify the body.