Root bifurcation lesions can be divided into four degrees according to probing and radiographs, as follows: 1. Degree I lesions: superficial periodontal pockets are formed, bone is mildly resorbed, the probe can detect the shape of the root bifurcation, but cannot penetrate the root bifurcation. 2. Degree II lesions: bone resorption occurs in the root bifurcation, no contralateral penetration is formed, some alveolar bone and periodontal membrane remain, and sometimes vertical resorption of periodontal tissue can occur. 3. Degree III lesion: root bifurcation, all the alveolar bone is resorbed, the probe can pass through the root bifurcation, the surrounding area is covered by soft tissue, and only exposed in the periodontal pocket. 4, degree IV lesion: all the bone in the root bifurcation area is destroyed, accompanied by heavy gingival atrophy, reaching below the root bifurcation, and the root bifurcation area is completely exposed in the oral cavity.