Okay, no fair! This throws a monkey wrench in my MSG theory!
I've had dentures for 7 years, and use Fixodent. I do have small gums, so use very little, but still....

ADDITION:

This made me research myself. Found a link (provided by Fixodent at http://www.fixodent.com/questions-and-answers.php) that may help answer some questions about Zinc toxicity and safe values.
http://ods.od.nih.gov/FactSheets/Zinc.asp