everyday-lifefriction
Certain "whitening" toothbrushes are sold and I was wondering about the mechanisms behind the tooth whitening process. I suspect this is related to the shape and arrangement of the fibres, probably somewhat similar to how a microfiber cleaning cloth works, but couldn't find any authoritative confirmation.
So how does a whitening toothbrush work? I'm only interested in the physical effects – whitening toothpastes rely on their chemical properties so they're a completely different story.
The blades are at an angle. As the blade moves down it hits an air molecule and the air molecule "bounces off" toward you.
It's just like hitting a ball in tennis/baseball
This is due to a psychological effect known as Color constancy. Your brain seems to see something based on the context around it, for instance the blue image projected on the red wall may be more black than blue but your brain will compensate for some of that because you also see the red wall.
This is also the source of a number of related optical illusions. For instance consider the image below taken from here. The squares labeled A and B are actually the same color, but one looks dark gray and one looks white because tile B seems to be in a shadow and surrounded by dark tiles and A is not so our brain perceives that B must be lighter.
Here's another optical illusion that may be closer to your question. The center piece in both images is the same color (gray) which you can see here.
Best Answer
Whitening toothbrushes remove surface stains or to put it another way literally remove deposits that are darker than your teeth were before they were stained.