Anything coming out of the mouth is usually associated with words being spoken. We have an expression:"it's like pulling teeth". This is meant to imply that getting information out of someone is very difficult. If in a dream scene, the teeth are falling out on their own, it can imply the opposite kind of situation - one in which
you are too readily or too willingly providing others with information. This can be seen as a loss to yourself (as you would now be missing some teeth).
To relate to teeth dreams, one needs to give them their proper meaning, one based on their function or purpose. As we know, teeth allow us to chew food, that is, to process new food for thought that comes our way in order to be able to incorporate the new information into our existing body of knowledge - or in other words digest or understand it. What allows us to do this is our intelligence. Thus teeth would represent our intelligence. Where the teeth are breaking into pieces, it can simply imply that the intelligence (the information or data) being used is not very sound or reliable.
On a physical level of interpretation, falling out teeth or crumbling teeth can represent a falling out with friends. (Note how friends are responsible for providing us with information.)