Hello, Teeth may gradually become yellow due to aging, hereditary factors, poor dental hygiene, or excessive consumption of tea, coffee, tobacco and cigarettes.
In addition, high doses of antibiotics, climatic conditions, infection and improper metabolism can contribute to discoloring of teeth.
Mix a small pinch of baking soda to your tooth paste and brush with the mixture, rinse with warm water, daily. Or rubbing your teeth with orange or banana peal once a day also helps. Eating strawberry can also whiten your teeth. Avoid the things causing discoloration as said above.
Or else visit a dentist.