I think the average applicant applies once. At least from the people/predents at my school. The ones who usually don't make it are pretty below average around here.
I think it has to. The number of applicants has been increasing over the years but not the number of spots so people need to apply a second or even a third time. It kind of compounds on itself. Then there's the fact that dentistry is f***ing awsome, so of course, everyone wants a piece of the action and then there are even more applicants...
I think it has been going up. More applicants, same number of spots, it has to be. I applied as a 'no degree' the first time and didn't get in (it was worth a shot) and then applied a second time with a degree and did get in.