A couple of general thoughts:

The Principal-Agent Problem. Dentistry, like auto repair, is one of those fields where the customer is purchasing a service directly from a technical expert delivering the service. The customer is generally at a pretty severe disadvantage when it comes to knowledge of the subject. This makes it really hard for the customer to make an informed decision as to whether or not the service is required.

High- and low-trust societies. We seem to be in a period of rapid decline of trust in our society (Western societies in general). I think we’re much more likely to see small businesses and other service providers try harder to take advantage of customers in a low trust society due to a lack of connectedness and sense of community. When people feel that they are part of a close-knit community they feel a responsibility to preserve those relationships so they tend to not try to take advantage of people.