Residual roots and crowns caused by caries, dental trauma and wear are a common clinical oral disorder. With the development of endodontic treatment technology, it is possible to preserve the residual roots and crowns after perfect root canal treatment for a long time, and to preserve them in the form of pile crown restoration, avoiding patients’ bad luck of tooth extraction. What are the advantages of preserving root remnants and crowns? 1, the retention of the root is conducive to maintaining the height of the alveolar bone There is an interdependent relationship between the tooth and the alveolar bone, the alveolar bone develops with the growth and eruption of the tooth, and is maintained according to the health and function of the tooth and periodontal tissue. If the tooth is removed for any reason, the resorption and shrinkage of the alveolar bone is accelerated. Preserving the roots not only preserves the alveolar bone around the roots, but also slows down the resorption of the bone tissue between the roots, thus maintaining the height of the alveolar bone and facilitating the restoration of the denture. 2. Preserving the roots preserves the role of periodontal proprioceptors The periodontal membrane around the roots is one of the important organs involved in masticatory activities, and it is rich in proprioceptors that can receive mechanical stimulation. Clinical studies have confirmed that both natural teeth and roots with dead pulp can identify the size, thickness, hardness, thickness and texture of food masses as long as the periodontium is present. Therefore, retaining the roots retains the physiological discriminatory ability that natural teeth should have, enabling them to feel the direction of force, control the size of force, and improve chewing efficiency. 3, retaining the roots of teeth to improve the support and retention of the denture Retaining the roots of teeth as the abutment teeth of the overdenture, compared with the mucosa-supported denture, its support role is greatly improved. The more abutment teeth there are, the greater the retention force; the more decentralized the abutment teeth are, the better the stability of the denture.