Well, so far so good for my kids. Breastmilk is still acceptable cos no sugar ... lol If it is formula milk, yes, you will have to make it a habit for them to brush their teeth after milk time at night to prevent tooth decay. My #3 and #4 still latch and they are fine with beautiful teeths. My #3 is 2 yrs old and #4 is 9 mths old.
this is something which i been pondering. My 2nd son tooth start to develop these brown stains. I wonder if its the latching issue that it's affecting it.
With my daughter, I would dampen her bib with water and gently wipe her teeth and tongue :)