The NBDE (National Board Dental Examination) is a exam dental students take after completing two years of dental studies in the US. There are two parts. Part one is a theory exam, while part two is a clinical exam.
Foreign dental graduates wanting to pursue a career in the US are required to complete Part one before beginning a two year continue education program specifically for foreign dental graduates. While part two is not required for admission into the continue education programs, some students have part two passed, which makes a more competitive application.
For more information on the NBDE you can visit the American Dental Association's(ADA) website.
ADA.org: National Board Dental Exam Part I (NBDE) 