Baking soda. Just apply some small amounts on your brush and use it like it's tooth paste only powder form. Use it 3 times a week and not consecutively each day. This can whiten your teeth but it can also kill some gum cells that protect your teeth form bacterial intrusion. It has something to do with controlling the pH levels in your mouth. Bad bacteria responsible for breaking down enamel of your tooth creates acid and baking soda is alkaline and neutralizes that acid.
But too much exposure to alkaline will also kill your own gum cells. Use it sparingly. Another method is avoiding foods and beverages that stain teeth. I'm talking about coffee. Cigarettes also stain teeth.
I have always heard peroxide. I have tried it a couple times and it makes you mouth feel extremely bubbly afterwards and I always have to rinse my mouth afterwards with water to get rid of it. It does seem to work though.
in my opinion, there are several things that must be done so that white teeth naturally.
First, avoid smoking. smoking causes teeth to turn yellow. Because the nicotine content contained in cigarettes will stick to the teeth.
second, avoiding drug use. as is often the case, someone who uses drugs will cause damage to his teeth.
third, brush your teeth 3 times a day. in the morning, after waking up, during the day, and at night when going to sleep. and a lot of people now do tooth brushing only 2x a day. when you wake up and when you want to sleep. in my opinion it is not enough for health in the teeth. so you should brush your teeth 3 times a day. so that the teeth remain white and healthy.
In my opinion, that is the only way to naturally whiten teeth.