We've spoken with several dentists who tell us it's not illegal to keep the teeth -- but most dentists either throw them away or give them to dental schools for research purposes.
Dr. Bill Dorfman -- a world famous dentist who treats some of the biggest stars on Earth -- tells TMZ he keeps a "secret stash" of the teeth he's plucked from the mouths of his famous patients ... in the hopes of eventually selling them on eBay.
Dorfman -- who recently treated Lindsay Lohan and whose website features Jessica Simpson, Usher, Ozzy Osbourne, Anne Hathaway and Eva Longoria -- was outside Rock & Brews in El Segundo yesterday when he revealed his secret.
"I actually save famous people's teeth when I pull them ... but I can't tell you [their identities] 'cause it's like patient confidentiality."
He continues, "There have been a few really famous people and I thought one day maybe I could sell this on eBay."
Dorfman insists he always offers the teeth to his patients first ... but they often decline, "So I put it in the back and i just hold on to it."
One dentist told us, "What Dorfman is doing is just sick."
We spoke to Doc Dorfman today on TMZ Live, and he changed his story -- drastically. Check it out ... around the 16-minute mark.