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."

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.

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.