I Am Currently A Junior In High School. I Am

I am currently a Junior in High school. I am sure that i would like to go to college to be an orthodontist. I am unsure on how the college years go, and the classes i would need to take. I am also wondering what would be best for me to major in during college. Could you please explain to me what i would need to do year by year and after i get done with undergraduate classes.