It's going to be interesting to see how this one plays out. The labeling on the packaging for fixodent saysto use a small amount, I know personally when I'm instructing my patients in denture adhesive use, that I tell them to use just 3 or 4 pea sized dots of adhesive.
The problem it seems with the zinc in the adhesive is from people who choose not to follow the directions on the packaging, and apply a large quatity of adhesive to their denture multiple times per day. These people would likely benefit more from a trip to their dentist for a denture reline or a new denture being made, or some implants to retain their denture then from a trip to the drug store to buy another tube of adhesive!