Your opening sentence seems to miss what I actually said.But it's okay to use the time of a teacher with 5 years of training? It's not just a question of cost and convenience, it's a question of effectiveness. I'd question how effective a one-off lesson from a teacher is going to be compared to a lesson from a medical professional who has just checked your teeth in detail and knows exactly which bits of your mouth are the problem areas.
Kids teeth aren't rotten because they're not getting a lesson in brushing their teeth from schools, they're rotten because 40% of kids in the UK no longer have regular dental checkups. Teeth are the leading cause of hospitalization for children. The budget for dentistry in the UK has stayed at 3 billion for a decade, which in real terms, is a huge cut in funding. But I wonder how much this lack of funding has cost the rest of the NHS who have to clean up the mess.
But if children were taught how to look after their teeth then there wouldn't be as many "problem areas" to deal with.
You could send dental students on visits to schools as part of their training.
This has come down to the best way to prevent tooth decay in children. With NHS dentists in short supply, and children's teeth in a poor way, the only issue is whether to leave it to parents - which by definition is a failing policy.