Source As the article says (but i have my own opinion) :

If you lack white teeth, you can point your finger at many things: coffee, cigarettes, Coke, Soya sauce, red wine, cranberry juice etc. This is why it is important to have a glass of water while consuming these products. On the other hand, there are natural items which help us whiten out teeth in a natural way: apples broccoli, spinage, celery and strawberries. Before you decide to undergo a chemical procedure to get whiter teeth, create a homemade paste which will give you that pearly white smile you used to have.

Strawberry

Rub a whole or crushed strawberry on your teeth. They do wonders thanks to enzymes which they contain, which make teeth whiter and clean sediments. Since strawberries contain sugar, it is recommended you clean your teeth with toothpaste afterwards.

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It’s up to you to use soda or not: I would advice SAFE method of Whitening Teeth at home. I have tested on my self:  My Method step - by - step, with pictures

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Orange or lemon

The inner side of orange zest includes teeth-whitening ingredients. Rub your teeth with orange or lemon zest and the results will be even better if you put some salt on the zest. Clean your teeth with toothpaste afterwards.

Apple vinegar

Make your teeth whiter with apple vinegar, although caution is required, because the acid can damage your gums. Mix a teaspoon of apple vinegar with half a glass of water – this makes an excellent mouth wash and if you repeat the process every day, you will see your teeth becoming whiter and whiter.

Baking soda

Mix a teaspoon of baking soda, some salt and a few drops of apple vinegar. Brush your teeth well with the mixture which will slightly foam. In the end, clean your teeth with toothpaste.
Hydrogen

Many types of toothpaste and whitening products contain hydrogen peroxide, known as the best teeth-whitening agent. Mix a teaspoon of hydrogen, a teaspoon of baking soda and water. Rub your teeth well, and be careful not to swallow because of hydrogen. In case this happens, drink at least one glass of water so that it dissolves in your organism. Use this method once a week, trybeautytips writes.

My BEFORE and AFTER teeth photos (other method - the best method tested by my self)