I did exactly that as a matter of fact...
On my first attempt at applying, I could not get into a dental school. Presumably my GPA was not spectacular (3.0), since I did try all the other tricks in the book (lots of research, observing, applying early, a 21 total on my DATs, what have you).
So I worked for a while and attended a masters program in biology, maintained a 4.0 GPA in the MS program, and got into two pretty good dental schools on my next try.
Yep, going to a graduate program first is definitely an option..