Why would they do it for pennies there if they could do it for a lot more money in the US? Lack of malpractice insurance, no need to be properly licensed, etc....
The average dental student graduates with $300k in tuition debt in the USA. In Costa Rica, tuition is free for their citizens. Plastic surgery is also very cheap in Costa Rica, few of the surgeons are members of the tribe and are highly recommended. On a 4 night trip, I did both crowns and plastic surgery.
Note, lots of the dental clinics that are geared only to tourists are owned by business man / marketing professionals, not by dentists themselves. The one I went to, I saw both locals and foreigners using it and it came highly recommended from friends in Miami.
There are also lots of other countries where dental tourism is popular, ie Columbia, Thailand, etc. Europeans tend to go to Eastern European countries for dental work. Not to mention, the dental schools / universities in Eastern Europe are filled with Israeli students.