I never went back. I found an older dentist and every patient in the office was a retiree, which made me feel confident they knew what they were doing (I'm sure they've got a lot of hard cases). I asked about the possible cavity and they said they saw nothing, everything is fine.
That's all just to say that the young dentists likely have a lot of debt between school and office build outs, and I wouldn't be surprised if they're up-selling services to try and get their practice out of it. I wouldn't trust them any more to be honest about practices just because they're young.
Highly capitalized, expensive leasehold improvements plus obscure pricing and surprise charges seem to be the typical playbook of that business model.
Reliable doctor-owned dental practices seem to be increasingly hard to find, at least here in the urban Southeastern US