When I applied I read:
- A UKCAT book
- Getting into Dental School
- Basic Guide to Dental Procedures
It would be worth doing some quick google searches into key topics that might come up in an interview such as caries, water fluoridation, amalgam vs composite.
And also reading a bit further into anything that you might see during work experience. If you buy an oral anatomy or operative dentistry book, it'll probably put you off applying :P
And of course ask around in this forum, it's an excellent resource. I'm a dental student at King's so i'd be happy to answer any appropriate questions.
Cheers.