I did research on WhatClinic, TripAdvisor, and a number of random blog posts people made about their experiences abroad. I found several that sounded good, talked to all of them, and went with the one that just felt right.

The dentists there had been trained at UCLA, and their coordinator was a Johns Hopkins alumni, so I felt really comfortable with both their level of education and their command of English (to minimize potential for misunderstandings, since my Spanish is barely enough to understand telenovelas).