flanaganse

As a US kid in the 2000s my dentist would give some kind of foam fluroide treatment. Foam would be put into two trays and you'd have to keep them on your teeth for two minutes. I remember hating it because it made me nervous I'd swallow some.

I still get fluoride treatments from my dentist but now it's something he paints on, perhaps the same as what you've described.

Anyway, according to a dentist friend, whether you get cavities is also dependent on the natural groves in your teeth. Some people's genetics cause them to have more cavity prone teeth than others.

Without insurance you can often get reasonably priced dental care at dental universities if you have one local.

At least for anything students can work on (fillings, extractions, etc). If you need a root canal, ortho, jaw surgery, or etc then I doubt it'll be a great option.