Major in something you are passionate about studying, not something that you merely think will make you look good to dental schools. If you are that passionate about biology, by all means go ahead. If you have your heart set on going to dental school, your time as an undergrad will pretty much be your only chance to study something unrelated to dentistry that you are passionate about.
The ADEA guidebook will tell you requirements for each individual school, but in general, they consist of two semesters of biology, two semesters of general/inorganic chemistry, two semesters of organic chemistry, two semesters of physics, one semester of biochemistry, and two semesters of English. When you get to college, talk to a pre-health advisor at your school about which courses at your university correspond to these requirements. For the science courses, it will generally be the introductory sequences. Again, the requirements for each school vary, so it will be your responsibility to ensure that you have the requirements for your schools of interest done.
You don't need to worry about preparing for dental school until you are actually in college. If you were hoping to get AP credit for the any of the dental school requirements during your senior year, note that a good number of dental schools DO NOT accept AP credit for fulfilling their requirements. If the university you choose to attend gives you AP credit for any of their courses, for the purposes of dental school admissions, you will either have to repeat those courses at your university or take advanced courses in the same subject area to make up for it. Also, even if a dental school of interest says they accept AP credit for their prerequisites, they will still want to see you take advanced courses in the disciplines for which you received such credit in order to show them an actual college grade in the area.
