Hi all, I've heard that if you leave a bottle i...

Hi all, I've heard that if you leave a bottle in babys mouth (when they have a nap or at night time) it can do some damaging stuff to their teeth etc. Just wondering if keeping the boob in there would do the same thing? I breastfeed DS in the morning in my bed then we fall asleep together. Some days I wake up and he has my nipple in his mouth, it's not as if I'm constantly flowing in there, he's pretty much emptied it already and just uses it for comfort. What do you think?