This goes in the "I'd rather not know" category... just like rats in restaurants, roaches at starbucks, and all the rest. Everybody knows it happens, but until somebody tells you about it, you're blissfully unaware.

It's why we have immune systems I guess.

Edit -- If you think this story is gross, you don't want to know how your toothbruth gets "leveraged" in the cleaning process. Keep em hidden!