Dental Examination to get in?

I've noticed that some programs require both a physical and dental exam to get in.
How important is the dental exam and what would prevent you from being approved?
I have some dental issues that I can't afford to fix (part of why I'm going back to school). I don't want to get stuck in a catch 22 of "I can't get into school because of my teeth but can't fix my teeth until I go to school and get a job".

Thanks for your imput