I was ASDA political advocacy chair in my local chapter last year when the dental therapy bill was proposed a 2nd time in the Arizona state legislature (it died early the year before). We spent a lot of time on this issue, coordinating with the Arizona Dental Association, and testifying before lawmakers why dental therapists as proposed in the Arizona bill would not work and actually presented a danger to the public.
The bill that was proposed here in Arizona was brazen to say the least. Dental therapists would have only required 3-years of training after high school and been allowed to perform anesthesia and nearly the full suite of restorative dental procedures. Additionally, they could perform simple extractions, and pulpectomies, all without direct supervision by a dentist. Imagine, someone with three years education, to your eight, having a large scope of practice without knowing the implications or fully understanding the risks. That bill was the camel's nose under the tent, as Arizona would have been the incubator for the same kinds of dental therapy laws around the nation. "They train them in three years in Arizona, and look how good it's worked out!" As the AzDA pointed out to the state legislature during hearings here, there was no data to track malpractice from DTs in Alaska (the place they used as an example of how effective DTs are) because the malpractice claims fall under the overseeing dentist. So, when DTs claim they have a "perfect record," they are in essence lying by omission.
I'll give you two good reasons Dental Therapists are not a good solution for access to care issues:
1.) Dental therapists in Minnesota are largely collected in the Minneapolis-Saint Paul area working at private clinics under doctors who are often running Medicaid mills. Access to dental care in rural areas of Minneapolis has not budged since the introduction of dental therapists. In the end, dental therapists want to live in the same places that dentists do. Why wouldn't they?
2.) The New Zealand model of having dental therapists in the school system to provide preventive dental interventions has not had a significant impact on childhood caries in New Zealand's schools. Furthermore, overall caries incidence across New Zealand has increased slightly over time, particularly in remote regions, suggesting that dental therapists have been ineffectual at preventing this increase or providing better care to rural populations. The same may be said for Minnesota and Alaska as well.