You can get tooth decay from milk it doesn't have to be formula. We got warned by our dentist not to give milk last thing at night always clean teeth last as milk has natural sugars in it.
A friend of mine only ever let her dc have milk or water to drink and her son got a couple of fillings. She was told it was the natural sugars in milk and water is basically the safest option for bedtime drinks.
The odd filling isn't quite the same as a mouth full of rotten teeth. That must be caused by other things too not just bedtime drinks. I also think the bottles themselves must be to blame as they keep the liquid in the mouth.
No child over 1 actually needs a bottle, it's pure lazy parenting. They can't be arsed to go through the initial upset of taking the bottles away so basically they just let them keep on having them. It's the same with too much food,tv,computer games,sweets,bad behaviour etc etc. Some parents just don't think they have any responsibility and want an easy life,they simple can't be arsed to get off their backsides and actually parent. They then expect the state to pick up the pieces in schools,hospitals etc. It really makes my blood boil,if we all parented in the same way it would be total anarchy.
I've taught in areas like this and you can throw whatever info,money you like at some parents and it won't make a jot of difference.