There are several reasons for yellowing of teeth: 1. Exogenous staining due to plaque and tartar adhesion, which generally requires daily brushing and regular scaling to resolve. In addition, you can also use teeth whitening methods, that is, cold light whitening. 2, pulp necrosis, if the tooth is impacted by external forces, or if there has been a root canal treatment, the tooth may turn yellow or grayish brown after a long time, and in this case, if it is pulp necrosis, it may need to be treated first, and then you can perform internal bleaching. Finally, for a more aesthetic result, cold light whitening or restoration of veneers and porcelain crowns can also be performed. Therefore, different treatment methods are needed for different reasons.3. If the tooth is fluoride or tetracycline, the tooth also appears yellow or gray, this color can be filled with resin for small areas, if the large area or the whole tooth surface wants to get beautiful effect, you can choose dental veneer or crown restoration.