Do you mean humanitarian work or setting up shop and being a permanent dentist in a foreign country?
I went on a dental humanitarian trip with my church to Guatemala over a year ago. I paid my own way and was able to assist, take xrays, and observe so much. It was a blast.
However if you're talking about permanently being a dentist in another country, the predental forum might not be the best source of info. But who knows. I'm a dual citizen (Canada-US) and I'd love to know what is required to practice in Canada after getting licensed in the US.