I can honestly say hand on my heart it hasn't been a problem. When the top teeth first came in there was a few days when they left a slight mark where they rested but it's not possible to compress milk ducts with teeth - it doesn't work - so soon the latch adjusts and the discomfort went completely. I just relatched and it was fine.
The baby's mouth compresses the milk ducts with the area of the mouth behind the teeth and the tongue. Put your thumb in your own mouth now and give it a suck (noone is looking
). Make sure your tongue covers your teeth on the bottom (not the way we usually suck a thumb). Suck with your tongue - can you feel how your thumb naturally rests on your upper palate and you can hardly feel your top teeth. Your nipple is even further back than that - where the hard palate meets the soft palate.
The bottom line is that nature's not daft - breastfeeding happens throughout the mammal world with some pretty scarily sharp teeth around (think baby tigers!). Extended breastfeeding is historically the norm - it really isn't a problem with top teeth. I swear. Some people get bitten - but it's fewer than you might imagine - and in my experience the issue of teeth 'resting' for a few days while things adjust is about as bad as it gets. Good to be prepared though!
The most pain I've ever experienced is pre-teeth clamping down at around 3-4 months.
