Most of the crown of a tooth is missing due to decay, and the crown is basically missing, and only the root remains, which is called residual root. Once the residual crown and root are formed, the pulp cavity and root canal of the tooth will be exposed to the bacterial environment of the mouth, and the bacteria can reach the root tip through the root canal, forming periapical inflammation and making the tooth a focal tooth, which may further cause other diseases of the whole body. In addition, the continuous stimulation of the oral mucosa by the residual root and crown may cause some lesions, such as oral ulcers and cancer. Root and crown remnants should be treated as early as possible and in time. In the past, most of them were extracted, but with the progress of oral material science and the improvement of restoration technology, the residual crowns and roots of permanent teeth, as long as there is no obvious resorption and loosening, can be treated with thorough root canal treatment first, and then restored to its appearance and function by root canal staking for full crown restoration, or retained for overdenture restoration. Not only the functional and morphological effect of the denture is good and short, but also it reduces the trauma of one extraction and avoids jawbone resorption after extraction, so the residual root and crown should be retained as much as possible. Only when it is obviously loose, or has long-term chronic irritation to the oral mucosa, extraction should be considered.