I'm told by my dad that his (private) dentist as a kid also used to be awful; whereas my (NHS) dentist was great. Though I'm told that surgery went downhill when our dentist retired. Very hard to separate out what's going on.

And I think essentially all NHS dentists do private work as well these days. The one bit of private work I've had done was a rear filling: standard amalgam was covered on the NHS tariff, but a cosmetic 'upgrade' to a white composite one was private and at cost.