Some border towns, like Algodones, specialize in a particular medical service. For Algodones, it is dentistry. There are other medical services there, of course. But people needing dentistry would obviously look there.
For other medical services, however, if you can travel further inland to Mexico's interior, you will find the largest community of expatriat Americans is found around Guadalahara, and most densely, nearby Lake Chapala. As a result, Mexican medical professionals who seek to earn slightly better than they can elsewhere in the country tend to migrate there as well, to serve the often well-funded retirees. There are many discussion forums on the internet about the subject of seeking medical services in Mexico. Sometimes this is called "Medical Tourism".