Excessive amounts of grinding (bruxism) or crunching down heavily on your teeth in your dream(s) strongly suggests to me that your levels of anxiety concerning where your life is currently heading are particularly high at the moment when you are awake.
Dreaming of teeth falling out in pieces may mean that you are feeling particularly insecure.
Such dreams often happen at a time of transition or major change between one phase of your life and the next one.
When each of us lose our baby or milk teeth (approaching our teenage years), we also slowly but surely in most cases lose our sense of childhood innocence.
Losing your teeth therefore may symbolize that in recent days you have had similar feelings of uncertainty and self-consciousness as you once did when you were about to leave your childhood permanently behind you.
As if you no longer feel that you have any sense of direction or purpose in your life, and that you are now entering a previously unknown grown up world or no man's land between no longer being a child, but not quite yet fully being an adult.
The dream could also be over dramatizing or exaggerating (as our inner dream director often tends to do, in order to get your urgent focus of attention) your current concerns about getting older or of having to change your ways of doing familiar things and thinking about the "big, bad world out there" and the people who are living in it, outside of yourself.
Trying to put your teeth pieces back into your mouth may therefore represent you wanting to go back to how you were before these changes started, and by so doing attempting to deny the reality of the situation that you will continue growing in spite of any resistance on your part.
Crawling around on gritty asphalt and rummaging through a grimy rubbish bin looking for your fallen out teeth suggests to me that you are presently looking in totally inappropriate places for the answers you are seeking to your many questions about just where your life is now leading you.
EoT
