Question For Dentists, Orthodontists, Or People Training To Be Either.?

Hi guys. Am entering my last year in Secondary School -high school- and i know what i would like to study when i finish school, orthodontics.
I would like to become an orthodontist.
My question is; Do you have to study dentistry and THEN orthodontics, Or would i be able just to study orthodontics and NOT dentistry to become an orthodontist?