I am amazed that you think you want to be a dentist and you haven't even picked out a college yet. I wasn't sure what I wanted to do ever. Just make sure that you don't rush into a field of medicine without exploring other options. If you go to a liberal arts college you're going to have to focus on the sciences that are required a lot earlier than if you go to a larger university. Make sure you leave yourself room to take a few different classes other than what's required of you. If you pigeon-hole yourself this early in your life you may get burned out quickly when you actually get to dental school.