With my limited experience so far, undergrad is proving to be a real help in relevant areas. Gross anatomy is the first course they threw us into, and my undergrad anatomy was probably the weakest course in my entire degree. Needless to say, I'm struggling to lift myself into B territory. In molecular cell bio and SABS (systems approach to biomedical sciences), however, I feel like I'm starting out way ahead of the game thanks to my undergrad experience.
A lot of people will tell you to major in something you enjoy during undergrad, and I respect tremendously those people and their advice...but I have to advise getting as much biology under your belt as possible during undergrad. It'll be a big help in dental school...and if you don't enjoy biology in undergrad, what on earth makes you think you'll enjoy it in dental?