depending on the location of the dye

External whitening This type targets external pigments that are formed due to environmental factors including smoking, food and beverage dyes, antibiotics, and metals such as iron or copper. The colored compounds from these sources are absorbed into the acquired deposits present on the tooth or settle directly on the surface of the tooth, which leads to the appearance of pigments.[6]
Internal whitening This is done to treat internal tooth discoloration that occurs as a result of a structural change in the thickness or composition of the hard tissues of the tooth. Yellow/gray discoloration caused by tetracycline administration.[16] Unlike external whitening, which whitens teeth from the outside in, internal whitening whitens teeth from the inside out. Internal whitening includes making a hole that reaches the upper part of the tooth nerve and is cleaned and then isolating the root canal with a material to protect the filling and usually sodium perborate is used in this process. [17] It was found that using a hydrogen peroxide solution may be aesthetically successful in the short term. However, in the long run, the success rate drops to less than 50% because it may cause a risk of root erosion [18] This process is repeated and the amount of time between appointments varies from patient to patient until the desired shade is achieved and is difficult to determine before treatment is completed.