He got his first two teeth a couple of weeks ago. Sometimes he clamps down (to slow the flow or hold nipple while he looks elsewhere) and it really hurts. He doesn't care if i scream, (he looks annoyed at me if i do), and pushing his face in my breast doesn't seem to do anything, (he just stays limp when i do that).
I make a big reaction and poke my finger into my baby's mouth. My DS hated this and it only took a few times before he learned (and he got teeth early at 4mo). Just keep playing with things until you find something that causes a reaction.
My DD was a persistent biter and she'd make me bleed. No matter what I did, she didn't stop. I started giving her Camillia by Boiron and she stopped. I'd give her a dose before we started nursing and it was a world of difference. I also used lanolin on my nipples because they stung from being bit.