Teeth whitening is a procedure that lightens the colour of your teeth, hence they appear brighter and whiter in colour. It helps to remove stains and discoloration but it will require more sittings time to time in order to maintain the brighter colour. The outer most layer of a tooth is called enamel. The colour of a tooth is basically based on enamel and the colour of the dentin under it. If the enamel is thinner then it allows more of the color of the dentin to show through and if it is smooth, again the colour and reflection of the tooth is affected. The most common factors that lead to yellow or staining of teeth are – tobacco usage, drinking liquids like coffee, cola, tea etc., unhygienic oral practices. It is also possible to have stains inside the tooth and these stains are known as intrinsic stains.