When the gum covering the root surface is no longer attached to the root surface for mechanical, pathological or physiological reasons, different degrees of root exposure will occur, and the root will be directly exposed to the oral cavity, saliva and various hot and cold stimulation environments, and the deep pulp of the tooth, which should have been protected by the root, will be subjected to the corresponding oral hot and cold stimulation to produce soreness and sensitivity. At the same time, due to the exposure of the roots, the supporting tissues around the roots are reduced, and the teeth may also become loose to varying degrees, or even fall out. It is especially important to note that gingival recession and root exposure can occur regardless of good or bad oral hygiene. In the case of good oral hygiene, it is usually associated with brushing, toothpick trauma, and tilted displacement of the tooth lip, while in the case of poor oral hygiene, it is often accompanied by loss of bone on the adjacent surfaces of the teeth and the crestal apex of the alveolar bone, which is manifested by extensive gingival recession on the adjacent surfaces of the teeth. It often involves multiple teeth and often appears as a blockage, which is commonly known as the black triangle phenomenon.