I think the difference is that ultrasound/imaging is routine annual from dentist and monthly or whatever from OB during pregnancy, but otherwise requires a spec

I think the difference is that ultrasound/imaging is routine annual from dentist and monthly or whatever from OB during pregnancy, but otherwise requires a specialist referral for a specific injury or complaint. It's also the case that a pregnancy is a hugely obvious invisible but major health situation, and teeth are expected to rot frequently.