You've probably read on Pinterest or Facebook that activated charcoal can be used for teeth whitening. There are many positive reviews from users that swear their teeth are much whiter after brushing them with activated charcoal. You can buy this from a health food stores in tablet form. For details how to use this as a teeth whitener check this article. But make sure that you do a little research of your own before trying this method.
All Natural Charcoal Teeth Whitening, 'Tuxedo' Tooth and Gum Powder By Rocky Mountain Essentials. Coconut Activated Charcoal and Bentonite Clay Formula is another natural alternative that can whiten your teeth. Contains no synthetic additives, preservatives, foaming agents, fluoride, artificial colors or flavors, and no abrasive baking soda or salt. Most of the user reviews are positive and they also offer 100 % money back guarantee if you're not satisfied with it. /buy on Amazon/
Also you can check out this cool video from my favorite series 'Beauty Hack or Wack' and see how you can actually apply this method. It looks kinda scary for a moment but once you rinse off the charcoal and your teeth are white and shiny again, everything looks great.