Tooth discoloration is caused by exogenous or endogenous staining, and requires periodontal or intra-teeth bleaching treatment; brushing with salt cannot whiten teeth. 1. Exogenous staining is caused by poor oral hygiene, resulting in the interaction of bacteria and food debris to form a large number of yellow or dark brown tartar and calculus; it will adhere to the surface of the teeth to make the teeth yellowish and discolored, and periodontal treatment (such as ultrasonic scaling) will be required to clean up the tartar or calculus in order to restore the teeth to their normal color. 2. Endogenous staining refers to the hard tissues of the teeth during the development of the teeth are affected by water or drugs (e.g. fluoride, tetracycline agents) appearing inside the teeth pigmentation; the discoloration of the parts of the teeth is the internal tissues of the teeth, must be carried out in the teeth of the internal bleaching treatment, that is to say, the use of special oral bleaching agents such as hydrogen peroxide on the oxidation and decomposition of pigments, in order to achieve whitening purposes. Tooth discoloration is recommended to consult a doctor for symptomatic treatment, and should not be used on their own to avoid unnecessary damage to the teeth, such as prescriptions.