What are you trying to fix? We'll need to know your GPA and DAT for a clearer picture of what you're lacking.
If it is a DAT problem, then the only solution is retake the DAT and apply early.
GPA issue, well it gets tricky. If you're hovering around ~3.0-3.2, then look into either an SMP with guaranteed linkage into their program (not sure which dental schools have this), but it is assumed you have a high DAT before you can apply to SMP programs. If your GPA is like a 3.4ish, than a year of postbacc would be fine.
Informal post bacc and postbacc programs associated with dental schools are about the same so go to the cheapest one. Only focus on postbacc programs that have a guaranteed linkage program or a very high post-bacc -> same dental school acceptance rate.
If it is both DAT and GPA, focus on DAT first, then look above for options regarding GPA repair.
Good luck!