J.,
I suggest that you switch to water in the bottle or sippy cup when he goes to bed. Explain that he is a big boy now and that milk is for meal and snack time. He can have milk in the morning. I'm sorry, but you may have to just sweat out a few tantrums on this one. Milk is very bad for his teeth while he is sleeping the sugars will destroy the enamel surface if this goes on for long.
My nephew had to have all his front teeth capped before he was four, because of this exact problem. Sam was so embarassed by his teeth even at that age that he contorted his mouth to hide his brown pointed teeth. The family had problems understanding him and he refused to smile. The caps made a huge difference, but it was an avoidable sittuation. My sister-in-law still blames herself for his continuing dental problems.
When you are ready to potty train you will need to cut back on the water at night as well. We are doing this with our daughter right now. She knows that she only gets a little bit of water in her cup, about 2 ounces at the most.
Best of luck,
J.