I do not this it is a "requirement" per say for most dental schools that you HAVE to have a 4 yr degree to get in, but 90 credits and the pre-reqs. That being said, it depends on the school as to what their normal operating procedures are. Some school don't require a 4 yr degree, but virtually all of their students have one. Other schools aren't so strict. For example, when I interviewed at Louisville, they had quite a few students w/o a 4 yr degree(so one of the students there said at least). The moral of this story is, even if you don't get a guaranteed program of some sort, you can still apply to schools after you have 90 credits assuming you have good stats and DAT's and all. As others said, private schools may be your best bet. As for Louisville, they are a state school and have a great program. It just so happens that the state of Kentucky has 2 schools and produce more dentists than the state needs, so instead of shutting down one school they let in more out-of-staters. (again...that's the story I heard at the interview) There may likely be other schools like this too.
Best of luck!