howdy stranger, where have you been? All I can give you is my own experience. I have 4 ancient Amalgams and I've had no ill-effects from doing this..I don't know if that's because most of the mercury is long gone...I know that there are those who would argue that with me on that:)
At any rate, I use the waterpik between the teeth and at the gum line, not on the fillings...
WHERE have you been? I was just thinking about you(no lie). :)