I went on a dental mission through International Service Learning. It is an agency stationed in Kansas City, and they have sites all over Central America and one in Africa. Very organized and reputable. I just found them on the internet...but they have a direct link from the Texas A & M Study Abroad page, so that put my mind to rest. I would highly recommend them. Thier website is very informative. I went to Costa Rica/Panama. I have heard from people in the ISL office that Panama and Nicaragua are locations that need more help.... just something I picked up. The cost includes most food, lodging, and transport while you are in the country. Airfare is on your own.
www.islonline.org
As an undergrad I was able to do cleanings, extractions, and fillings, Plus your world view will never be the same. It was truly life changing. It gave me a very good look at dentistry. I would highly recommend doing something like this...not just as an line on your resume, but something that will make you a better professional and human being.
Hope this helps.