Teeth whitening gum; the effects seem short term. How does it work?

Does it mearly coat the teeth in a whitening substance?
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Xylitol is a natural, sugar-free sweetener that can not be "digested" by the cavity-causing bacteria in your mouth so that acid can't eat away at your enamel and you are less likely to get cavities. It really doesn't have much effect on the level of staining. Many whitening gums (like Orbit White) contain baking soda. The abrasive particles "scrub" your teeth while you chew. Others (like Trident) have a fancy name for something that whitens teeth, but if you look at the ingredients you'll find baking soda as well.
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