I studied math. My personal belief is that as an undergrad, you should study whatever it is you think you'll enjoy the most. If you can believe it, I really liked math. I also would have liked to have studied linguistics.
In terms of dental school, it's more important that you do well in school and on the DAT, not so much your major. If you ask me if a science degree makes you more competitive than a non-science degree, all else being exactly equal, I'd say there is a very, very slight advantage to the science major (but I think some others in the forum would disagree). But the advantage is only slight, and it's more important that you thoroughly enjoy your undergrad years, since you only get that once in your life.
Biology and Chemistry (BS) - studying a science (and understanding the process) will help you catch on to what they're really talking about in the main didactic science courses during your first year or so of dental school. However, I like to think of a dentist's undergrad degree as his/her "hobby." Your future dental school will teach you everything you need to know to be a competent dentist, but it's not like they will help you become a more well-rounded or interesting person. It's very healthy for professionals to have interests outside of science/dentistry - keeps you from going nuts. Anyway, to make a long story short - study your passion or at least something you're really interested in during undergrad - even if there's no way you would want to make that your profession. (I really like German lit, for example, but had zero desire to teach it or research it - i dropped the major a class away from finishing it to graduate early). You will still be taking the courses that will enable you to do well in dental school, while at the same time contributing to your future quality of life.
If you are simply really really focused on dental school - getting in, getting perfect grades, etc, - then take a major that allows you to "pre-take" courses you'll encounter during the "academic" portion of dental school. There are some guys at my school who majored in "medical biology" in undergrad which somehow allowed them to have already even have gross anatomy experiance coming in - very helpful.
I majored in Computer Science because it was a very valuable degree at the time, and I wasn't sure what I career I wished to pursue. I decided on Dentistry and completed my prerequisites while working.