drinking from the bottle might let the milk stay in their mouth when they sleep. and bathing teeth in milk for a long period of time have prove to lead to tooth decay. that's why they say they should change to sippy cup by one yr old (cos they usually have teeth by 1-yr-old).
i personally think that drinking milk from the bottle before they sleep is a way the baby unwinds. & it's a form of comfort & security for them (at least for my little 13 mth old, it obviously is) my little one refused to drink anything else in the bottle since i introduced water at 6 mths (she's been breastfed until one-yr, but takes the BM in bottle sometimes). she only likes her milk in the bottle. anything else (water, diluted juice, etc) she wants from a cup (w/ a straw, she hates sippy cups). if i put milk in a cup, she looks at me funny. my ped said as long as i make sure that she swallows her milk after she's done & never fall asleep with the bottle she's fine. it's even better if i let her have a sip of water after the milk.
i think the thing about weaning from the bottle from 1-yr is because you see all these toddlers carrying their bttles around w/ milk, juice, etc in it, and keep sucking at it thru-out the say. which means that their little teeth are bathing in milk, juice whatever all day, which is why we should let them use a cup instead.
i think as long as you let them finish their milk in one go, and don't them carry it around w/ juice, it's fine.
