There are two kinds of tooth discoloration:

Extrinsic discoloration refers to stains on the enamel (the outer layer of your tooth) that can look like yellow tints, brown spots, or white streaks.
Intrinsic discoloration refers to darkening of the dentin (inner layer of your tooth) into a yellow or grey tint.

Intrinsic discoloration is much harder to reverse, and may require a cosmetic treatment like veneers. However, extrinsic discoloration can usually be taken care through a variety of whitening techniques.There are many over-the-counter remedies that can do this, but the effects only last for a certain amount of time. More importantly, they are merely covering up the real issue--the bacteria and other stain-causing molecules that build up on your teeth.The benefit of using natural remedies is that they take care of the root of the problem to give you the most natural-looking white smile possible. Here are some natural remedies that have proven quite successful at reversing tooth discoloration, and restoring your pearly-white smile.

Oil Pulling

Oil-pulling is actually a very old remedy, dating back 3,000 years, to the Indian Ayurvedic medicine system. Oil-pulling involves swishing about a tablespoon of oil in your mouth for about 20 minutes. Studies have shown that it helps to remove plaque, fight gingivitis, and kill the microorganisms that cause bad breath.

You can use coconut oil, sunflower oil, olive oil, or other standard cooking oils. However, it is said that sesame seed oil works best, specifically in "whitening" the teeth. While the other oils have the same cleaning and disinfecting effect, they don't have the same whitening ability as sesame oil.

Tips for Oil-Pulling

If 20 minutes is too difficult, start with 5 and work your way up. The whitening benefits usually don't start until you can swish for 15 minutes or more.
Only use a tablespoon. As you swish the oil around in your mouth, it oxygenates and grows. You may find that any more than that will be too much will cause you to want to spit it out. Oil is expensive...no need to waste it.
You don't have to swish very hard. 20 minutes is a long time. If your jaw gets sore, swish more gently.
Don't swallow or gargle with the oil afterward...it will contain all the bacteria that it pulled from your mouth and you don't want that staying in your body. Spit it out!
Spit it out in a trash can rather than down the sink--oil clogs drains.

Strawberries

This one may seem strange...because we all know that fruit is acidic and therefore can wear away at the enamel on our teeth, making them more susceptible to stains...But, the malic acid in strawberries can help remove surface discoloration on your teeth. You just have to make sure that you brush your teeth afterwards to keep it from eating away the enamel.Mixing strawberries and baking soda, makes for an even more effective solution.

Mix crush 1 strawberry and mix it with 1/2 tablespoon of baking soda until it is thoroughly blended.
Brush it onto your teeth using a toothbrush
Leave on for 3-5 minutes
Rinse your mouth thoroughly and brush using toothpaste
Make sure to get any stray seeds out with floss

You should only use this treatment once weekly as the citric acid can damage your enamel if applied too regularly.

Baking Soda & Hydrogen Peroxide

Hydrogen peroxide is an anti-bacterial agent, while baking soda works to scrub the teeth because of the grittiness of the substance. The free radicals that this mixture creates works to break down stain-causing molecules that rest on your teeth. You can then brush away the remnants.

Combine equal amounts of baking soda and hydrogen peroxide
Mix them into a paste
Brush your teeth as you would with regular toothpaste
Be sure to rinse thoroughly and brush with toothpaste afterwords

You can also use baking soda by itself, or mixed with your toothpaste. Just place some toothpaste on your brush, then dip it in the baking soda, and brush like you normally would, rinsing thoroughly afterwards. Follow-up brushing with just regular toothpaste.

Apple Cider Vinegar

Though Apple Cider Vinegar can take up to a month to do its job, many say that it bears results closest to that of a professional teeth whitening. It works particularly well on coffee and nicotine stains. It also makes a great gum cleaner.ACV is an acid, however, so you have to take the same precautions as you would with citrus peels and strawberries. Rinse thoroughly afterwards and brush your teeth with regular toothpaste. This will keep the acids from wearing down your enamel. You can brush with ACV, or simply put some on a cloth and run it over your teeth.

Brushing / Flossing

When it comes down to it, there is no replacement for regular brushing and flossing. Many people think that flossing is just to get chunks of food out from between your teeth, when you can't loosen them with a brush.

Actually, flossing is meant to reach the plaque and small, undetected pieces of food are underneath your gum-line. That is why your dentist nags you about it--because it is just as important as brushing.Many people were never taught the right way to brush and floss either.

Talk to your dentist about proper brushing and flossing technique and other important factors in oral hygiene.This is foundation to having healthy, white teeth. If you want whiter teeth, make sure you've got the basics down before you try these other remedies. It will accelerate their whitening effects.

A Short video on Brushing/Flossing: https://youtu.be/gepoVAR9PUg

Detergent Foods

No, its not like laundry detergent for your teeth! I had never even heard of detergent foods until recently. And you may be surprised to find that most of them are already in your fridge.

Cheese
Apples
Gum
Peanuts
Raw Carrots
Celery
Popcorn

What do all these foods have in common? They are natural toothbrushes. Their hard or sticky structures act like brushes or scrapers that break away food particles from your teeth, and clear them of acids that are left behind from the meal.It is said that you should wait at least 30 minutes after a meal before you brush your teeth, because the acids left behind to break down the food can be spread around your mouth and damage the enamel on your teeth, and leave it prone to stains. Eating detergent foods is a great alternative to making sure your mouth is free of stain-causing molecules if you don't want to wait that long or don't have a toothbrush handy.One reason for discoloration is the failure to clean your mouth regularly enough. We're busy people. We don't always have time to take a break 30 minutes after a meal to brush our teeth. BUT we can certainly grab an apple or a carrot to munch on while we work or are off to the next appointment.

Prevention

Both extrinsic and intrinsic discoloration are caused by the same things. When beginning to restore the whiteness of your teeth, it is important to not add further to the problem. Here are different culprits of tooth discoloration, that you should avoid (if possible) if you want whiter teeth. It is the simplest, yet perhaps most difficult part of teeth whitening.

Foods like coffee, tea, cola, wine, cherries, blueberries, and potatoes.
Smoking or chewing tobacco
Illegal drugs, as well as some prescription drugs--particularly antihistamines, antidepressants, and high blood pressure medication
poor dental hygiene
some dental materials, such as silver amalgam
overexposure to flouride

There are other factors such as age and genetics that you, obviously, can't control. But in those cases, the best you can do is be vigilant in your oral care and talk to your dentist about your concerns. together you can find the best solution to whiter teeth.