There are several threads on this but in a nutshell, post-bacc can be informal or formal. A formal post-bacc is often geared towards individuals that did not take pre-reqs while in undergrad. There are 1-year, 1.5-year and 2-year post-baccs and I think you get a certificate for many of them. The informal post-bacc just means you took classes after college. You do not get a degree, certificate, nor do you have an adviser that requires you to take certain classes.
I got a degree in biology but needed to raise my gpa so I did an informal post-bacc for 2 years, taking all upper-division biology courses. I wasn't too ambitious in college, only taking the classes I was required to take, so there were plenty of biology courses that I had yet to take. When I was in your position, deciding btwn informal/formal post-bacc, MSPs and MPHs, the schools that I called and spoke to told me that while getting a degree/masters of some sort is obviously not negligible, doing FULL-TIME coursework as part of an informal post-bacc will also help someone who's deficiency in their application is a low GPA.
In the interest of full disclosure, I am applying this year (tomorrow!!) and so clearly have not gotten into dental school. However, many people that I've spoken to, including people that have formerly been on adcoms, have echoed the same things I've described above.
Hope this helps.