The guy who is buying them up posted a picture of the Chael Grill Gear on twitter (@mrsamedmonson85). Looks like the pic is gone now. It was a brand new mouthpiece. You could see that it had never been molded to anybody's teeth.
Quick google search yielded these pics from Topps. You can see the mouthpiece is new.
Topps UFC trading cards include mouthpieces worn by Chael Sonnen and more - Los Angeles Trading Card | Examiner.com