Technically, anybody can become a dentist. But if you're in Dental Hygiene school, or plan on going to dental hygiene school, then you may already know; Most DH programs are 2 years long and some colleges offer a 4 year DH program. So if you plan on going to dental school, you'll want to get a 4 year degree in dental hygiene (you can get a 4 year degree in anything, but I know you're interested in Dental Hygiene). Most dental school have pretty similar requirements that you have to fulfill before applying to dental school, so be sure to check with the schools that you'll want to apply to a couple years down the road. Most want you to 2 semesters of organic chem w/ labs, 2 semesters of bio w/ labs, among others. You'll complete these requirements while obtaining your 4 year degree. You'll then want take the that (dental admissions test). You'll want at least a 3.4 overall GPA and a 3.75 science GPA with that scores of 20 or higher in all areas of the test to be competitive.
Good luck! : )