Before you sign up to another course, find out what it was about your application that caused you to be rejected, if there's something you can work on, that would be the smartest option (1 more year improving your application is better than 3 years of a degree you don't want and £27,000 debt)
If it's something like low GCSE's or something you can't really change now, have a look at moving abroad, there are dental schools within the EU that are accredited in the UK
I would advise against the graduate entry route, I honestly don't see a difference, they even say graduate entry is harder, if they wouldn't accept you now (for reasons you can't change) why would they accept you later? They tell you the minimum requirements are lower but look around you'll see the majority of successful applicants to these schools still have an impressive academic record