DS #1 was BF'd 24/7...healthy teeth (got them early at 4 months, upper two and bottom two a week later).
His teeth were super healthy, and I ate and drank alot of what he did when he was learning solids from 6 months on.
We shared food from my plate (come to think of it, I remember 'chewing' stuff and offering the softened up bits to him without even thinking about it).
At around 1 year he started eating cheerios (didn't know better back then)....and THAT's when his upper top teeth started looking wierd and he got cavities in them. Had to go to a pediatric dentist at 18 months because one chipped the end off! ACK!
She, (no kids of her own) said it was because I was still breastfeeding him! And that especially at night was soooo wrong, and I would need to stop that. She said (OMG, where do they learn this stuff???) that 'Once they have teeth, then they really should be weaned! and no more night feedings at all!' **Wean them at 4 months because of risk to teeth???!!**
HAH! Obvious she didn't have a clue about breastfeeding or a headstrong nursing toddler that loved to night cuddle/nurse.
Anyway, got his two cavities fixed (OMG what a trauma for a 18 month old) and then never went back.
DS#2 has upper teeth already (at 4 months) and again, teeth look great. I will just not let him have cheerios and other 'sticky' traditional snack carbs once he eats solids and will start a brushing routine for when he starts eating a few solids during the day (not starting him on solid training until 6-7 months)...
Just my experience. The S. Mutan thing had me worried, but I really do think it was due to eating 'sticky' carbs that are hard to remove and or a combination. The breastmilk probably saved his bottoms, as it 'rests' on them more.