Alison, maybe I'm in denial - Lisi won't drink milk from anything other than a bottle and dislikes most other dairy. There are a couple things I figure: 2 bottles a day amounts to maybe 8 minutes total with a bottle in her mouth so compared to the 12 hours sleep time with a dummy in her mouth that's pretty small fry. Better the bottle than no dairy (other calcium sources are even harder to get in her), most kids seem to get braces whether thumb suckers, dummy addicts, bottle users or completely viceless - my sister was in infant school and still sucking on her bottle every now and then - she was the only one of us that DIDN'T get braces (ok, ok, I sucked my thumb until I broke my arm aged 9 and couldn't get it into my mouth any more 'cause of the cast and my other sister still sucks hers - but hey!)
I think that more of the issue as pp has said is if the bottle is being used for all liquids or as a dummy replacement.