Lactation Consultant and other BFCs I've seen have said that teething doesn't affect feeding. I BFed DD for 20 months so managed fine with all her teeth.
But my tiny, poor gaining, 'failing to thrive' 17 week old has had his FIFTH tooth come through today. It seems logical to me that he may well have been in pain/ discomfort in his mouth since birth, so feeding may not be a very pleasurable experience for him. He's certainly never really been one for 'comfort sucking' and often doesn't want to feed or doesn't feed for long.
I can see 3 more about to erupt too. Poor little mite.