system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible to reverse yellowing of teeth by brushing harder? Or is tooth yellowing permanent?

Edit: wow, calm down mods! I'm seeing a lot of helpful comments being removed.
gpt
Staining isnt the only reason teeth turn yellow.  Enamel is white-ish but it's not completely opaque.  Dentin, the material underneath your enamel is naturally yellow, aging and natural wear thins your enamel making the dentin more visible. If you brush too hard you could just end up stripping away more enamel resulting in even yellower teeth.