Hi,
Actually, I'm pretty sure that Canadians can get US licenses (NERB, etc) on TN visas (without being green Card holders (permanent residents) and work as dentists in the US. However, I think they cannot open or buy a practice because the TN visa requires you to work for someone else. To own a practice, you then need to be a permanent resident.
The TN visa was set up to allow mobility for some types of professionnal in the North American market. NAFTA's goal is to get each country to "eliminate any citizenship or permanent residency requirement for the licensing and certification of professional services provided in its territory". This deregulation is to allow free movement of the most mobile and highly skilled groups of workers within the three countries.
The only thing is that you need someone (a company, an organisation) to sponsor you for this TN visa.
texas_dds: All you have to do is to take your NDEB and I think you also have to notify your provincial College of Dental surgeons to register.