Dear Dr
You can apply for Orthodontics programmes in the US, almost all Dental Schools in US as well as some hospitals offer training in ortho., however you have to attened at least 2 years in Dental schools after taking NDB part 1, and then after that you may apply to ortho. programme, there are also some school like New York Univ., that offers Ortho. trainig programme only to International students provided that they practice outside the US once they are done! but in General most school require you to get a DDS or DMD from US or Canadian Dental School
I hope that was helpful
Sincerly
Khalid Al-Hussein