I am breastfeeding my second child now for 18 months and counting. My first I breastfed for 19 mos.
My advice: Let it get ugly. Scream with pain when he bites. Let him get scared over your cry of pain. And...put the milk bar away. He needs to learn the consequences of his doing. Here: Biting hurts and will not be tolerated.
Once you've yelped your pain (you have every right to. After all they still are _your_ breasts), reprimanded him sternly that biting is an ouchy and a no-no (don't think he doesn't understand, cuz he does.), and packed everything away, then it is time to comfort him and distract him. I wouldn't try to breastfeed again until Griffin gives some signal of being hungry again. My experience shows me, that when a baby is hungry, they eat, and don't play around with their food.
Another thing you might try, would be to give him piece of fruit or veggies to gnaw on. Like a slice of apple, piece of carrot or cucumber sticks. Don't worry about this starting the weaning process. From Griffin's standpoint, he's got these two nifty things in his mouth that need to be tried out. What better way than with healthy foods? He can't really eat them yet, but it will get him used to the idea of solids and different flavors of food. I gave my daughter apple and cucumber pieces to play with with 2 months, and nursed her exclusively for 7 months.
This maybe more than you wanted, but I personally think that the nursing relationship is to precious, valuable, and short-lived to be thwarted by a couple of teeth :-)
Good Luck
Angie