Well I just did a long post about my positive experience with a US citizen, ADA member dentist in Progresso and the system lost it.
Recommend Dr X (Xavier Aguirre) if you need major work such as full dentures, partials or implants. He is a University of Texas BS-Biology grad, but could not afford US dental school and did his dental training in Guadalajara. He later earned his ADA membership, implant training in Texas and teaches continuing education classes in Houston and Austin on implants and cosmetic dentistry twice a year. He runs his own lab and turns around dentures, crowns, partials in 24 hours.
For smaller, simplier work - my wife uses the Zacaharias family. They don't speak english fluently, but do have fluent staff members on had to translate. They do not have their own lab, so thinks like the inlay she had done take 2 days turnaround.
I don't know about the laws in Mexico for becoming a dentist. I will say that Nuevo Progresso is a competitive dental, and medical, market for US/Canadian customers - and poor dentists don't stay in business long.
You will be greeted by the usual hustlers as you get across the bridge and past Mexican customs/immigration (which will usually wave you through without even looking at your documents). If you don't have a particular dentist in mind to visit, take their referral cards, look them over an visit at least three offices before making your decision. Personally I only will go to a dentist who is a member of the US ADA.
If anyone gives you a high pressure sales technique - get up and walk out the door. There is a better, more friendly dental office literally a few doors down.
Pricing - The costs are significantly lower than from a US dentist. You are not going to get the dentists exclusive time for the entire visits. The assistants are going to do most of the work that actually doesn't involve your teeth. The dentist will supervise and check everything. You won't get a lot of x-rays, they are frugal with supplies. They provide you safe bottled water (usually from Sam's or Costco) for rinsing, but it will be one 8 oz bottle.
But it will not be dirt cheap. My dentist charged $40 per extraction for 23 teeth, including any dental surgery needed to remove them. He charged $800 per set of dentures - which was two sets - the initial set and the implant set three months later. He charged $950 per implant for the two implants to hold my lower plate. That was $4,420. I spent about $100 for antibiotics and pain meds. (My dentist strongly recommends allowing the gums to heal and the implant bases to 'grow in' for at least two months between fitting the first dentures and setting the posts an the final dentures. The first dentures are mainly to help the gums heal into a good shape for the final dentures. Kind of like a cast.)
The best quote I had in the US was $10,000 for an identical two implant process, or $7,200 for one set of no-implant dentures.
My wife spent $190 for a cleaning and one inlay.
Payment - US cash is preferred and should get you a 5-7% discount over quoted price. Expect to pay full price up front. US checks are accepted by most. Canadian checks by fewer. Visa, Master Card and JCB are accepted almost everywhere, and Discover and Amex by most.
Drugs - Mexican dentists and doctors do not have DEA permits to write prescriptions to be filled by US pharmacies. You will have to buy any necessary antibiotics, pain meds, etc in Mexico. The dentists/doctors know to give you a prescription form, and keep the Mexican pharmacy receipt. US Customs/Border Patrol is very familiar with hundreds to a few thousand people coming back from Mexico with such drugs every day. When they ask if you bought anything - simply tell them you had dental work done and have the drugs the doctor prescribed. They may or may not want to look at the prescription and the drug boxes.
(Side note - I met two US trained dentists and one US trained doctor during our trips and border crossings. All were unable to practice in the US because of high school age drug convictions for marijuana use/ possession. They were very forthcoming about their dissatisfaction with the US dental/ medical schools who took their money for years of training, only to learn later that the FDA will not give them a license to dispense prescription drugs).
Safety - Nuevo Progresso survives on tourists, a great many of them seeking dental or medical care. Of course you want to be sure you have only what you need on you, and to be wary of possible pick-pockets. Though I've never heard of anyone having been hit. Think of it as a big city, like riding the subway in New York. Be aware of your surroundings.
Insurance - I haven't heard of any dentist in Nuevo Progresso taking a US dental insurance. Many of the MDs do take US insurance. None of the pharmacies take US insurance.
Medical Care - I know a half dozen people who use doctors in Nuevo Progresso for their medical care. All only need to visit their doctors a couple times a year. For chronic, frequent care - you need to live in the area. One of my friends has well controlled type two diabetes, visits their doctor twice a year and loads up on diabetic meds (metformin and glimepiride) and testing supplies for six months at about 20% of their US costs during each visit.
Other friends buy their long term maintenance drugs in Mexico with prescriptions for their US doctors.
I recommend using Mexico to save money, but do your due diligence in selecting a doctor, and don't be afraid to negotiate price, or ask for detailed explanations. Or to walk out the door and find another healthcare provider.
EDIT - One final note - Timing - Aug is when many of the Mexico dentist take their vacations, especially the ones who are US citizens/ residents who live in the US. They want to get that done before their kids go back to school on Aug 28 or Aug 21.