You need a box of baking soda, a lemon or bottle of lemon juice, and a toothbrush.
Mix 1 teaspoon of lemon juice with a small amount of baking soda, and form a paste.
Dip your toothbrush in the mixture, or scoop a bit of the mixture onto your toothbrush. Brush your teeth for the length of time you normally do. Be sure to use gentle, circular strokes for the most effective stain removal.
Rinse your mouth well with tap water. Even though lemon juice is safe, allowing it to remain on your teeth and gums causes sensitivity in the future.
Fruit juice stains teeth quickly. Avoid stains by only drinking one or two glasses of dark fruit juice per day. Drink your juice using a straw so that the juice doesn't come in contact with your front teeth. Eat plenty of raw vegetables to naturally scrub your teeth. Strawberries are also a natural teeth whitener.