Good question.
There isn't any public health done here, actually. At least not in the traditional sense.
During our fourth year we are away from campus on rotations, and those rotations can be assigned to us, or we can set them up on our own.
So, if you want to go down to Latin America on several rotations then you certainly can. Of course, you'll be expected to complete dental requirements while you are down there, so that sort of negates any public health.
Still, that doesn't mean you wouldn't have a chance to better the oral health of people in Latin America, it simply means you would mostly be dealing with patients rather than a group of people as a whole. I'd imagine there would be time, however, for some community instruction, but the point of the rotations is to practice dentistry in another area and to better your clinical skills.