There are many causes of abnormal tooth color, which can be either congenital or acquired. Congenital tooth coloring is caused by the symmetrical color change of most teeth at the time of tooth eruption, such as fluorosis, tetracycline, and enamel hypoplasia. The coloring of teeth caused by congenital reasons is normal at the time of tooth eruption, and the color of individual teeth gradually changes after the effect of adverse stimulus, such as after tooth decay or trauma. Fluorosis is the coloring of tooth surface caused by excessive intake of fluoride at the stage of tooth development. The more fluorine intake, the more serious the coloring is, in order of expression, chalky, yellow, light brown, dark brown, the coloring range can be part of the tooth surface and all of the tooth surface, and in serious cases, can also be seen in the tooth surface pit-like defects, both affect the aesthetic and dental quality. Fluorine only damages the developing teeth, so if you live in an area with high fluoride content in drinking water for a long time before the age of 6 to 7, even if you move to another place later, you cannot avoid the involvement of permanent teeth that will erupt in the future; on the contrary, if you move to a high fluoride area after the age of 7, you will not develop dental fluorosis. Tetracycline teeth are stained teeth caused by taking tetracycline family drugs during tooth development. The extent of the effect of tetracycline on tooth staining is related to the type of tetracycline family of drugs, the dose and the period of administration. It can appear as cadmium yellow, lemon yellow, or dark gray. Tetracycline drugs can enter the placenta through the mother’s blood circulation and affect the fetus, so tetracycline can cause staining of milk teeth and permanent teeth during the mother’s pregnancy or the infant’s own consumption of tetracycline. Tetracycline only affects the developing teeth. Generally speaking, it will not cause significant tooth staining when given after the age of 6 to 7. To prevent the occurrence of tetracycline teeth, the Ministry of Health stipulated in 1983 that tetracycline drugs should not be used in women who are pregnant and breastfeeding, and in children under 8 years old. Enamel hypoplasia is a disorder of enamel development in permanent teeth caused by systemic diseases, nutritional disorders or localized lesions of milk teeth in pregnant women and infants during tooth development. For example, severe malnutrition, hyperthermia such as measles, pneumonia and sepsis in infants, rubella and toxemia in pregnant women. Periapical infection of individual milk teeth can lead to hypoplasia of the permanent teeth in that tooth position. Enamel hypoplasia is mostly characterized by chalky white horizontal stripes on the enamel surface, or substantial defects in the form of bands or sockets, with yellowish dentin showing at the defect site. The enamel defects are also prone to pigmentation and caries. If the enamel development is caused by systemic factors, the affected teeth tend to be symmetrical, such as the hypoplasia of root-side permanent teeth due to periapical infection of milk teeth, which is manifested by small, irregularly shaped crowns and often gray-brown coloring. Poorly colored teeth can affect the aesthetic appearance of the face. The main treatment methods for poorly colored teeth are: Decolorization bleaching: the application of oxidizing agents or acid etching agents to eliminate the staining and discoloration layer of the teeth, thereby achieving the purpose of bleaching the teeth. However, bleaching is not effective for everyone and the specialist should strictly select the indications and protect the oral mucosa to prevent the gums from being burned during the operation. Decolorization bleaching can be divided into two types of bleaching: external bleaching and internal bleaching. External bleaching is mainly used for the decoloration of moderate non-defective fluorosis and tetracycline teeth. Internal bleaching is mainly used for discolored anterior teeth, unpulpable teeth or severely tetracycline discolored teeth. Composite resin coating restoration: a technique that has been gradually developed since the 1980s. It is a polymer composite resin bonded to the surface of the affected tooth to cover the discolored tooth or to repair a tooth defect. Veneer: It is mainly used for cosmetic restoration of anterior teeth that are neat, complete, and free of dental caries. There are resin veneers, porcelain veneers, cast ceramic veneers, and neo-plastic hard resin veneers. Cast ceramic and porcelain full-crown restorations Cast ceramic and porcelain full crowns are ideal for restorative and cosmetic purposes because their shape, color, transparency and luster are close to those of natural teeth. To make a full crown, 1-2mm of the tooth’s week is ground away, and sometimes the nerve is removed. In terms of color, full porcelain crowns have the best shade.