The bottom of the tooth should refer to the neck of the tooth, the neck of the tooth appears black covering usually consider dental calculus, plaque or caries caused. It is recommended to go to the dentist for a clear diagnosis. 1. Considering too much calculus and plaque, bacteria accumulate and produce biofilm to form plaque, and later calcification to form calculus, in order to avoid repeated stimulation of the gums, resulting in gingivitis, it is recommended to go to the hospital for scaling to remove calculus and plaque. 2. Considered due to dental caries, bacteria caused by dentin caries tissue lesions, there is also the possibility of foreign pigment staining, in order to avoid caries continue to aggravate caused by pulpitis, it is recommended to the hospital to go to the net decay for filling. In short, patients should do a good job of oral hygiene maintenance in ordinary life, the neck of the teeth appear black should be timely to the hospital for testing, under the guidance of the doctor for the cause of treatment.