Before reapplying, I'd try to figure why you weren't successful this cycle. If it's simply a matter of less-than-stellar DAT scores, then I'd recommend retaking the test this summer and getting the rest of your application materials submitted in June. If it's a serious GPA issue (sub 3.0), I'd consider waiting until after completing the post bac because you can take this year to seriously improve your GPA and (hopefully) throw in some extracurricular experiences that will make you a more competitive applicant.
I was in kind of a similar situation in that I'd been accepted to a post bac program and I decided to apply and take the DAT during the summer before the program started, but I decided instead to just take some classes at the school on a per-credit basis (i only took 3 classes) and research. I couldn't have made a better choice because I got several interviews in the fall, and I had plenty of time to prepare properly for them and travel around the country without worrying about balancing an intense courseload. I was in a couple of classes with the students in the post back program (i took the classes at the school that offered the post bac), and I know that I would've done poorly in my interviews, courses, or both, if I'd been trying to get straight A's in 5+ science classes while having to miss all of my Thursday and Friday classes every week for interviews.
The scariest parts of taking an extra year is that it is an extra year of your life and that you're losing a year of future "dental salary," but you should also appreciate that you're preparing to start a 40+ year career. A year spent devoting 100% of your attention to the post bacc (and doing well) and another spent meaningfully adding to your overall application will make you a lot more competitive and the time spent will feel like nothing when you look back on it.
Awesome is right- if you don't apply, nothing can happen. However, if you simply apply again this cycle (in 1-ish months), will your application have changed much from last year? Adcoms will 100% look to see what you've done to change/improve, and I imagine the only thing they're going to be able to judge you on is your fall semester of your post bacc- That's a lot of pressure to put on yourself this fall. As you know (since you applied last year), simply submitting your app takes a ton of time and money.
