Teeth bleaching principle: the main ingredient of common teeth bleaching agent is 10% concentration of urea peroxide, the decomposition of urea peroxide produces 3.3% hydrogen peroxide, hydrogen peroxide is easy to penetrate into the tooth enamel and dentin, which will break down the large molecules of pigmented material into small molecules, so that the teeth lighten in color. Bleaching methods: Tooth bleaching is currently divided into clinic bleaching and home bleaching. Clinic bleaching is the use of a high concentration of bleaching drugs in a special light source irradiation, generally 1 to 2 times can be, each time about an hour. Home bleaching is done by taking an impression of the teeth and making a thin, personalized tray, adding medication to the tray every day, and wearing the tray for 4-6 hours a day for about 1 month. Clinic bleaching has its own advantages and disadvantages compared to home bleaching: clinic bleaching has the advantage of being quicker, but more expensive and more irritating, home bleaching is slower but cheaper, and the end result of both is the same. Indications of teeth bleaching: the best adaptation of bleaching is officially orange and brownish discoloration of teeth, the best effect on the yellowing of teeth aggravated with age, the effect of mild tetracycline, fluorosis is moderate, and the effect of severe tetracycline, fluorosis is not good.