If at all possible, avoid ANY kind of metal in the mouth, not just mercury amalgams.
Also be aware that even white fillings can sometimes contain metals such as lead.
Be very demanding to know the EXACT ingredients/specifications of any filling material before you let a dentist put it in your mouth. Dentists are rarely (I didn't say never) to be trusted when asked about this. I would insist on seeing an actual product data sheet for the material a dentist intends to use.
If the dentist refuses to provide this or fobs you off, or tries to to imply that you're being fussy, paranoid, obnoxious, contrary, disrespectful, inappropriate or any other such negative thing, by asking him/her for exact specifications, WALK OUT OF HIS or HER SURGERY and FIND ANOTHER DENTIST. Dentists have put poison in the mouths of millions of people over the course of many decades, and are often too quick to dismiss legitimate concerns of patients. Self-education is your best defence against this.
Two useful resources, to get the ball rolling, are: