It is found that the long black plaque on teeth may be caused by chronic periodontitis. In the early stage of chronic periodontitis, gum swelling and pain, gum bleeding, bad breath and brown or black plaque will appear beside the teeth. If not treated in time, the gums will atrophy, the teeth will loosen and even the teeth will fall off. It is necessary to go to the dental clinic regularly for periodontal treatment for a long time. By cleaning teeth, calculus or plaque around teeth can be removed in time, inflammation of gums can be controlled, swelling and bleeding of gums can be improved, and bad breath will disappear. I should pay attention to keep my mouth clean, brush my teeth every morning and evening, and rinse my mouth after meals. Another reason may be that tooth decay leads to tooth nerve necrosis and teeth may turn black, so root canal treatment is needed in dental clinic.