Half of the tooth is missing, through clinical examination and X-ray examination to determine the degree of tooth loss, the assessment of the remaining tooth retention is carried out as follows: 1. If the tooth loss is manifested as root fracture, extraction is generally recommended; 2. If the tooth loss is manifested as partial crown loss, it can be restored by means of filling or full crown; 3. If the tooth loss injures the nerve, root canal treatment is required before restoration; 4. If the tooth loss is manifested as crown root fracture, for the loss within two millimeters under the gum, pile crown restoration can be carried out after root canal treatment, for the loss more than two millimeters under the gum, extraction is generally recommended.