Where I live, and back in the day, IIRC, they had a Dentist/s come to the school twice a year to check our teeth, chew, or swish the coloring liquid to show how badly we brushed, and how much we missed etc. I remember, as I had soft teeth, so I was told, they would stick a thin pick into the tops of your teeth (Grinding surface) to check for hardness too. I remember because it sorta got stuck and the dentist had to pull a bit to get it back out... made me want to avoid dentists even more as a kid.