This isn’t complete bunk. The new indicator of wealth is healthy teeth. Poor kids don’t get to go to the dentist regularly, so have more problems later on; rich kids get regular cleanings to prevent buildup, and have much healthier teeth.
The trick was making us equate white-white teeth with healthy teeth, even though there’s a shade of ‘white’ that is just healthy, clean enamel with no plaque buildup but isn’t true white.
I only retained this when I heard it as I was a poor kid and, wow, am I glad I have a good job as our dental care is still mercenary as fuck.