11 month old rests teeth on nipple while eating help!

So my 11 month old son has 8 teeth & for the past week or two he’s been resting his teeth on my nipple while he eats! It’s very painful and has caused me to be in pain during feedings & throughout the day🙄 I don’t think he understands that he’s doing it. I try to tell him no teeth & point to his teeth while shaking my head.. but he doesn’t seem to get it. I’m not sure what to do at this point! I tried different positions and such, but nothing is seeming to work. I’m always left with teeth imprints on my nipple when he’s done.!