Guidance for preschools around me is for them to brush kids teeth after every meal that’s served at school.
That was recently reinstated after being suspended for a couple years and the teachers are practically (as much as they legally can) begging the parents to sign the waivers to opt their kids out of it. I don’t blame them. It seems excessive and it’d take a ton of time for two teachers to scrub a dozen or so sets of toddler teeth, while also controlling said toddlers while they wait for everyone to finish.
There’s other factors than just brushing your teeth but brushing is probably the easiest factor that most people can reasonably take control of.
Genetics, obviously you can’t do much about. But you can avoid sweets and decide not to get pregnant (hormonal changes during pregnancy can cause mouths to get more acidic and make plaque harder to remove, and can also soften the gums and bones that hold teeth in, or even weaken the teeth directly). Also, if you want nice teeth, it’s especially important to abstain from smoking crystal meth. And that’s even more important during pregnancy.
But telling everybody “brush twice a day for two minutes” is a small ask with huge returns.