At first, I was going to say either is fine, but now that I think about it, going DH route might be a waste of time. It takes 2 years to finish and if you work after you graduate, that's another year or two. If you are doing it just to make your application better, it's probably better to do post-bacc/smp or masters to raise your GPA, which is probably what you need for them to favorably consider your app.
I believe that having been a dental assistant and dental hygienist can be helpful, but it probably will not trump GPA. Also, it takes longer than what post bacc or smp will take you. If you are looking for back up plan to fall back on in case you don't get into D-school, that's different story.
I heard similar things about MPH. It's not as helpful as doing well in smp/post bacc.