If I have white spots on my teeth, should I remove the stains by micro-abrasion BEFORE or AFTER using Crest White Strips?

I have very yellow teeth. And I have some yellow-brown spots and white spots on my incisors teeth. I want to whiten my teeth but I'm afraid the spots will remain. I have seen some photos with people with this problem that have used the product and have gotten good results, except from the white spots (they get even whiter). So I guess they don't dissapear using this product. I know that they can be removed with micro-abrasion. Should I do the micro-abrasion before or after using the product?

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