I used to have dreams of my teeth falling out and disintegrating when I was younger. Some of the answers on here may be right, but for me, my dreams always seemed to be about someone in my life's health. Everytime it happened, someone in my life ended up getting very sick or injured. That's probably not the case for you, especially if you could put your teeth in milk after they fell out, but I think it might have something to do with health, just not as extreme as my dreams. It could also just be a stress dream.