If black lines appear on the surface of the tooth, there are two possible situations that require different treatments for different situations. The first case may be the presence of soot spots, pigmentation, etc. on the tooth surface, and in this case the pigmentation is attached to the tooth surface and removal requires sandblasting treatment. The sandblasting process can completely clean out the pigmentation, smoke stains and discoloration on the tooth surface. After sandblasting, a regular polishing process is required to make the tooth surface smooth, so that the pigmentation and smoke stains will not be easily attached. The second situation is likely to be the existence of caries, in the early stage of caries formation there will be black lines on the surface, with the prolongation of time, it will make the yellow and white demineralization on the tooth surface locally, and even form local enamel defects. Once the early caries with black line is found on the tooth surface, we should brush the teeth carefully and apply fluoride locally to remineralize the enamel.