He did pay for teeth, and it's assumed that some came from slaves (They can't prove that he used them for himself, but they were purchased). However, the bottom line is that he paid for them, he didn't just take them, and he never forced anybody to give up their own teeth. He also had pairs made of ivory and other elements, including his own teeth.

Btw, it wasn't uncommon back then for people to place ads seeking to pay for teeth.