It could be from a galvanic reaction, some dentists believe there is an order to removing the amalgams to prevent this...I think it may be in Huggins or Cutler's books.

You can read more about it here...

http://www.medical-library.net/sites/framer.html?/sites/_dental_amalgam_mercury_poisoning.html

Hope you feel better soon.

Sandi
xoxo