Peroxide decoloration can be applied to treat mild and moderate discolored teeth. There are generally two types of peroxide decolorization: dead pulp teeth and living pulp teeth, which can be called internal bleaching and external bleaching respectively. Internal bleaching is usually performed by a doctor, first of all, the dead pulp teeth must first undergo proper root canal treatment, that is, to prevent the infected material inside the tooth from invading the tissues around the root, and then the bleaching drug is placed in the pulp cavity and root canal of the affected tooth for decoloration, usually using a high concentration of hydrogen peroxide, i.e. 30%. For external bleaching, there are two types of bleaching: in-office bleaching and home bleaching. In-office bleaching uses a higher concentration of bleaching medication, usually 30% hydrogen peroxide, mixed with a small amount of excipients for ease of use and to reduce accidental burns to surrounding tissues, and special devices can be used to assist with light to improve results. In-office bleaching is fast-acting and the treatment can be completed in a few sessions. Home bleaching means that the hospital provides special tooth bleaching trays and home bleaching agents for the patient to use on their own, mostly using peroxide for safety reasons; it takes a long time to work. Severely discolored teeth are difficult to correct completely by bleaching alone, and are generally treated by bleaching plus restoration, i.e., using porcelain veneers or all-porcelain crowns to cover the color on the basis of bleaching, or even taking porcelain crowns with opaque bases for overall coverage.