If the gap between the teeth and gums becomes black, it should be judged differently. If the gap between the teeth becomes large, resulting in a black gap, which is called black triangle in medical science, this is caused by the destruction of the dental bed around the teeth, that is, the bone, and finally the tooth decay. There are also other conditions that can cause the gap between the teeth to become black, such as periodontitis, which is originally caused by plaque, tartar, and tartar. Especially the tartar under the gums can be exposed after the gums recede, and after it is exposed, some patients will be more concerned about it and think that the blackening of the gap between the teeth affects the beauty. There are also some common cases where there is no abnormality in the periodontium itself, but the teeth themselves have problems, especially tooth decay. Many patients plug the gap but never floss, plaque will cause demineralization on the surface of the teeth, after demineralization the teeth will rot further, and after decay the teeth will become black. Some of the blackness can be seen through the outside or inside, and a faint blackness can be seen. In this case, if the decay is mild, a filling is needed, and if the decay is serious, root canal treatment may be needed. Whether it is filling or root canal treatment, it is not done in periodontal department, but in endodontic department of dental hospital for standard treatment.