In the natural world you use your teeth to grind the food before you swallow it.
So the teeth become a front row processor of the resources that are coming into your mouth.
Since dreams often have spiritual and emotional symbolism, you need to translate the role of the teeth into the spiritual world.
Your soul and spirit does not need physical food, but it is very much influenced by the information that comes your way. Information can produce fear, sadness, anger, etc.
So your teeth in the spiritual dimension represent the filters in your soul with which you interpret the information that comes your way. Your opinions, past experiences, love relationships, etc. all are the key factors growing your spiritual teeth.
When you dream your teeth are falling out that means that something is going to happen in your life that will cause to totally remove any preconceived opinions or points of view you currently have.
For example, you can be a huge fan of one news station and you swear they are always telling the truth. One you you learn that the truth is that they were always lying to you...that is when the teeth fall out.
There is no way for me to know what you believe and what will happen that will cause you to change your points of view.
But this dream should only caution you to be careful what you believe, and be open to questioning everything, so that one day you don;t learn you were brainwashed by someone.