They used to go to the dentist, I assume regularly. Then they stopped, I think they had probably stopped before the first lockdown but they certainly never went back once appointments were becoming more regular for routine check ups again, so they can't even use the excuse of having moved and can't find one. And to be honest, they drive around so often anyway I would happily drive back to the old dentist they had already been registered at if I could not find one closer that was taking new patients. They have the time so could have done that, except they will have been taken off the list long ago by now. They could also spend some of the money on it rather than buy more vans, lawnmowers, skates, sofas or a 50th ride on vehicle for Jace.
I remember Isla having a tooth out and they claimed that she just has bad teeth, it's not their fault. I suspect like most things that's a lie given what we see them eat and general lack of personal hygiene. However, I do have a child who does have weaker teeth for no apparent reason (said by the dentist, not me!). The hope is that the big teeth are normal and it's just the baby teeth affected, and thankfully we haven't needed any treatment yet. Because of this, my child has appointments every 3 months rather than the 6 months that the others have. I can't imagine if they had been told Isla is unlucky enough to just have teeth more susceptible to damage/decay why they would ever think the solution is to just stop going to the dentist at all!