The first reason is that there are stains in the teeth, most of them are due to the habit of smoking or drinking colored drinks, and the stains can be cleaned up by scaling and sandblasting. In the second case, if there is caries on the surface of the teeth, the teeth will not only be black but also form cavities, the depth of caries can be determined by taking x-ray film, and the shallow caries can be filled with resin after removing the black material to restore the beauty of the teeth. If the decay has hurt the nerve of the tooth, root canal treatment is needed, and then crown restoration will be done.