The 65-year-old Li Bo, a few years ago removed all the roots of the teeth, because the alveolar bone is low, wearing a denture loose, often open mouth fall, he regretted that the root of the tooth was easily extracted. In the end, is it necessary to pull out all the tooth roots and crowns? The value of a crown in the oral cavity depends on the condition of the tooth defect, the length of the remaining root, and the health of the periodontium. If the crown can be used as an abutment for some kind of restoration after systematic periodontal treatment and root filling, then it can be retained. If the crown is too defective and the tooth is very loose, it should be extracted to avoid becoming a potential source of infection in the body. The root and crown remnants in the mouth are mainly caused by dental caries, wear and tear, traumatic fracture, etc. It can cause periodontitis, periapical periodontitis, bad breath, traumatic ulcers, tongue cancer and other oral diseases. Long time embedded food makes the place of residual root and crown become the breeding place of bacteria, forming the source of infection and causing gingivitis, periodontitis and other local infectious oral diseases, causing long-term chronic pain, bleeding, redness and swelling, loosening of teeth and weakness of chewing. Severe periodontitis sometimes spreads from the lesion to adjacent teeth, leading to inflammation and/or loosening of adjacent teeth. The residual roots and crowns in the mouth can easily hide food and are not easy to clean. The bacterial growth and reproduction can also cause bad breath and inconvenience to the social activities of the patient. Long-term tooth loss can cause occlusal disorders, causing displacement of neighboring teeth and elongation of the opposing teeth, reducing chewing function and possibly causing temporomandibular joint disorders, resulting in unnecessary joint pain and difficulty in opening the mouth. If a tooth defect forms a sharp tooth tip, repeatedly rubbing the oral mucosa and soft tissues at the tongue and cheek, it will cause repeated traumatic ulcers or even ulcers that do not heal for a long time. What is more serious is that the sharp tooth tip constantly damages the oral mucosa and becomes a long-term chronic adverse stimulus, which may become a carcinogenic factor (such as causing tongue cancer and cheek cancer). Patients with root and crown remnants should be seen in a timely manner and treated correctly with the professional advice of the doctor. Do not take lightly the oral problems caused by root remnants and crowns, and avoid easy removal to affect future restoration, as well as avoid the possible harm caused by long-term neglect. Retaining roots and crowns with retention value should be preserved as much as possible 1. First of all, in the root with pile core material can be fixed denture restoration (such as porcelain teeth, all-ceramic teeth), simple, beautiful, comfortable, and does not wear adjacent teeth. It has an important role in maintaining the stability of the tooth alignment. 2. Special devices (e.g. magnetic, button attachments, etc.) are installed on the roots of the teeth to support the retention of the movable denture above them, so that the denture is not easy to loosen and fall off and improve the chewing efficiency of the denture. If all the teeth are extracted and the remaining alveolar bone is low, then the full denture is often loose and painful, so we can only rely on dental implants to increase the retention stability of the denture. 3, the retained roots are buried in the alveolar bone after treatment, which can slow down the resorption of the alveolar bone and maintain the height of the alveolar bone; it can preserve the proprioceptors of the periodontal membrane, which is favorable for patients to perceive the size and shape of food, control the chewing strength and improve the chewing function. In addition, the retention of residual crowns and roots contributes to the patient’s psychological health and slows down the degeneration of the brain. For some elderly people who cannot tolerate tooth extraction (such as those suffering from systemic diseases like hypertension, diabetes, heart disease, etc.), and with the fear in their hearts, most of them are reluctant to remove the residual roots and crowns in their mouths, the residual roots can be preserved by turning the harmful roots into harmless roots through root canal treatment. Women should treat the residual roots and crowns before pregnancy to avoid the effects on the fetus from extractions or infections requiring medication during pregnancy. Therefore, the residual roots and crowns in the mouth should be treated promptly, and those that can be preserved after treatment should be treated restoratively, while those that cannot be preserved should be extracted promptly. At least the sharp tips of the teeth should be rounded and smoothed.