Post-radiotherapy dry mouth is one of the serious sequelae of conventional radiotherapy in patients with head and neck malignant tumors such as nasopharyngeal cancer and oral cancer. The main mechanism is that radiation damages the cells of the adenohypophysis and the ductal system, causing the atrophy of the adenohypophysis and the loss of function of the main salivary glands, such as parotid glands and submandibular glands, which leads to post radiotherapy xerostomia. Pathologic manifestations include glandular fibrosis, fat deposition, follicular atrophy and necrosis of glandular cells. When the irradiation dose reaches 10 Gy, the secretion volume decreases significantly, and dry mouth, mucous membrane congestion, burning pain of oral mucous membrane appear, and when the irradiation dose reaches 30-40 Gy, the symptoms become more obvious. Almost all patients had different degrees of dry mouth after radiotherapy, which was manifested by frequent drinking of water, using soup to help stirring and swallowing food when eating, and also led to pain, taste, speech and sleep disorders, and a large number of dental caries, which seriously affected the quality of survival of patients with head and neck tumors after radiotherapy. Therefore, to find a simple and effective treatment method for dry mouth after radiotherapy for head and neck malignant tumors, so as to improve the quality of life of patients, is one of the urgent and important topics of clinical research at present. Transplantation of submandibular gland is a new treatment method to prevent dry mouth after radiotherapy for head and neck tumors, which has been proved to be effective. Studies have confirmed that dry mouth after radiotherapy is mainly due to the damage of salivary gland function and the decrease of secretion. Under normal circumstances, each submaxillary gland can secrete 200-300 ml of saliva per day, and if one submaxillary gland is preserved, it is possible to prevent dry mouth caused by radiotherapy for nasopharyngeal cancer. Therefore, in order to alleviate dry mouth after radiotherapy, radiation to salivary glands should be avoided or minimized as much as possible. So is it possible to transplant salivary gland tissues into the radiation field before radiotherapy to protect the salivary glands from normal salivary secretion and oral health to prevent the occurrence of dry mouth? The latest research of scholars at home and abroad confirms that transferring the patient’s submandibular gland to the sub-chin space before radiotherapy, and shielding and protecting this part during radiotherapy, compared with conventional radiotherapy, can maintain sufficient saliva flow even after radiotherapy, which can effectively reduce the occurrence of oral dryness after radiotherapy and improve the quality of life of patients with nasopharyngeal carcinoma, oral cancer and other malignant tumors of the head and neck. At present, submandibular gland transfer to prevent dry mouth after head and neck radiotherapy has achieved good results in both animal experiments and preliminary clinical experiments, opening up a new way to prevent radioactive dry mouth. Submaxillary gland transfer is a simple, safe and effective surgical method that scholars are exploring to prevent dry mouth after radiotherapy. Indications and contraindications of submandibular gland displacement As a clinical treatment for preventing dry mouth after radiotherapy, submandibular gland displacement also has strict indications and non-indications. The specific manifestations are as follows: (1) Selecting patients whose first lymph nodes of metastasis from nasopharyngeal carcinoma and other cancers are not lymph nodes in zone I. The prerequisite for submaxillary gland translocation is that there is no lymph node metastasis in submandibular and sub-chin regions, i.e., zone I of the neck, so all the lymph nodes found in the region should be examined by intraoperative pathologic freezing. If there is positive lymph node metastasis in neck area I, submandibular gland transposition should be abandoned. (2) If the submaxillary gland of patients with nasopharyngeal cancer or oral cancer has its own dysfunction, or if the patients have undergone radiotherapy before surgery, they are not suitable for submaxillary gland transposition. 3. Surgical method The operation adopts conventional submandibular incision, and the mandibular marginal branch of facial nerve is protected during the operation. All lymph nodes in the submandibular region were excised and sent to frozen pathology biopsy to confirm that there was no cancer metastasis. The proximal end of the external maxillary artery and the anterior vein were ligated in the retroventral plane of the bicuspid muscle to protect the submandibular ganglion, and the blood supply of the submandibular gland was supplied from the distal extra-mandibular artery and the anterior vein in the reverse direction. The submandibular muscle was partially cut off, and the free submandibular gland was moved to the sub-chin region by using the distal part of the external maxillary artery and the anterior vein and the duct of the submandibular gland as the tip, the submandibular gland was fixed to the deep anterior abdominal surface of the diastasis muscle by absorptive suture, and the metal wire was fixed around the gland as a marker for the position of the gland during radiation therapy. Drainage strips were placed and the wound was closed in layers. 4.Submaxillary gland displacement —- Gospel for head and neck radiotherapy patients Traditional radiotherapy prevention and treatment of dry mouth often uses improved radiation therapy techniques with intensity modulation radiation therapy (intensity modulation radiation therapy ,IMRT) or three-dimensional conformal radiotherapy techniques to optimize the dose distribution, protect part of the parotid gland, so as to preserve some of the functions of the salivary glands. The results of the study have confirmed that three-dimensional radiotherapy is the most effective way to treat parotid glands. It has been confirmed that IMRT is not effective in preventing xerostomia; in addition to the selective protection of parotid tissue by the protective agent amphotericin during radiotherapy and the use of salivary secretion stimulants such as cholagogues after radiotherapy, these measures are also commonly used in clinical practice for the prevention and treatment of xerostomia. However, these measures are often accompanied by adverse effects such as nausea, vomiting, hypotension and heart rate changes, and some clinical studies have confirmed that there is no significant difference in the degree of dryness between patients protected by drugs and those who did not use drugs; in addition, the use of artificial saliva or lubricating fluid to alleviate radiological dryness of the mouth is also partially efficacious. Submaxillary gland transfer is being explored as a simple, safe, and effective surgical procedure to combat dry mouth after radiation therapy. Compared with the traditional treatment, the submandibular gland can be successfully relocated to the sub-chin region, and with appropriate shielding, adequate salivary flow can be maintained even after radiotherapy, which can effectively reduce the occurrence of oral dryness after radiotherapy and improve the quality of life of patients with head and neck malignant tumors. At present, although the clinical indications and possible complications of submandibular gland transfer for the prevention and treatment of dry mouth after radiotherapy still need to be explored, the therapeutic advantages of submandibular gland transfer as shown in the existing studies indicate that its use will provide a new dawn and a gospel for radiotherapy patients to reduce and avoid the pain of dry mouth.