We've lived at Lake Chapala for 3+ years full-time and know the medical and dental scene well.
Dental Express is certainly the most aggressive in its pricing but there are many, many other options here. My wife's and my favorite place overall is Chapala Dental Care (
Chapala Dental Care - Lakeside Ajijic Dental Clinic & Dentists, 01-376-765-5584). Dr. Consuelo Sanchez is our go-to person there and they also have very skilled endodontists on staff. Have sent U.S. friends there for everything from routine cleanings to emergency root canals an all have been very happy.
The dental (and medical) scene here is very competitive and there's a decades-long history of people flying down, getting a lot of work done and spending a couple of weeks vacationing in the area and still coming out thousands of dollars ahead of U.S. prices.