I don't know about the whole teeth theory. I've never seen any footage of him chewing and showing pain (even when he drinks those weird milkshakes), it seems to me that he pulls those pained faces when taking a bite because he has a horrible flabby droopy face that squishes up whenever he does anything. He has a Shar Pei face.
Edit: Also if you had fucked up teeth, doing that swishy liquid chewing thing he does seems counter-intuitive. If your teeth are sensitive, you'd immediately swallow it so it has as little contact with your teeth as possible, not the opposite which is to swish it around and have it hit all your teeth.