According to Huggins book "It's All In Your Head", many dentures use an oxidated form of mercury for the red coloring.
Might want to check this out also.
Sounds like your dentist is not being very honest with you. I wonder why there would be silver under the ceremic. Also, ceremics have aluminum which, I've heard, have bad effects, especially when mixed with mercury.
Sorry for all the bad news. I guess today it's, "Let the buyer beware." Too bad it's come to this.