1) baking soda  
2) hydrogen peroxide雙氧水(You can replace hydrogen peroxide with salt. Salt is even more abrasive so reduce the frequency.)
(3) normal toothpaste

Mix a teaspoon of baking soda with a few drops of hydrogen peroxide, brush your teeth with the mixture (should be a paste form substance). Rinse with water. Then brush your teeth with toothpaste as normal.

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