In the treatment of head and neck tumors, radiation therapy is a very important treatment tool. However, radiation therapy can cause a variety of oral complications, such as: oral dryness, mucositis, radiation osteonecrosis, local infection, tooth sensory hypersensitivity, rapidly progressive periodontal disease, loss of taste, and difficulty in opening the mouth. Among them, oral dryness is the most common, its incidence is almost 100%, and 89% of them are moderate – severe. The normal flora of the oral cavity of patients with dry mouth is changed and more pathogenic bacteria are produced, which causes the loss of tooth components too quickly and leads to tooth decay; dry mouth also makes the oral mucosa dry, cracked, painful and ulcerated; it also affects the functions of chewing, swallowing, speaking and sleeping, causes malnutrition and affects social activities. All of these have a negative impact on the quality of life. I. Composition of salivary glands Salivary glands include parotid, submandibular, sublingual and minor salivary glands. The first three are collectively known as the major salivary glands. The parotid gland is a plasma gland that secretes plasma vesicles rich in water and protein; the submandibular gland is a mixed gland composed of plasma and mucus vesicles; the sublingual and minor salivary glands are mainly mucus glands. The parotid gland is the main gland that secretes saliva after stimulation, and its secretion mainly serves to moisten food and make it easy to swallow; the rest of the glands play their main role in the unstimulated or resting state. When stimulated, the parotid gland secretes 60-65% of the total saliva, the submandibular gland 20%, the sublingual gland 2-5% and the minor salivary glands 10%. When unstimulated, parotid secretion accounted for 20%, submandibular for 65%, and sublingual for 7-8%. Some authors suggest that unstimulated salivary secretion plays an important role in oral health, while post-stimulation salivary secretion reflects glandular function. Although the secretion of the minor salivary glands is small, its main component, mucin, accounts for 70% of the total mucin; some authors suggest that the recovery of oral dryness is mainly the result of mucin secretion [13]. The daily salivary secretion in adults is about 600 ml, and even 1000-1500 ml has been reported. II. Radiation damage to salivary glands Radiation damage occurs mainly in the alveolar and ductal systems, causing alveolar atrophy and chronic inflammation of the salivary glands. Plasma alveoli are more radiosensitive than mucus alveoli, so the parotid gland is the most vulnerable of all salivary glands. After radiotherapy, salivary secretion is reduced and its composition is altered; these are dose-related and can be long-lasting. However, during and several months after radiotherapy, the secretory and dividing functions of the glandular vesicle cells recover to varying degrees, but are accompanied by degeneration of blood vessels and proliferation of connective tissue fibers; eventually the gland shrinks and adheres to the surrounding tissue. In some cases, glandular components can regenerate and sometimes these regenerations are functional, depending on the size of the radiotherapy field, the radiotherapy dose and the age of the patient. Some authors suggest that the mechanism by which late radiotherapy damage to the gland occurs is a delayed manifestation of sublethal damage, which occurs during the turnover of dead cells; others suggest that radiotherapy causes mucosal damage due to: radiotherapy-induced copper and iron ion-catalyzed redox promoting free radical reactions; or because the function of electrolyte fluid secretion regulation in the parotid gland is more impaired than the function of cellular drainage. Several methods have been used to reduce the dryness of the oral cavity caused by radiotherapy, such as: protecting the parotid gland with IMRT or 3D conformal radiotherapy; using salivary secretion stimulants – cholinomimetic drugs to prevent and treat oral dryness; using radiotherapy cytoprotective agents – amphotericin to transplant the healthy submandibular gland to the subchin area for protection. All these methods have different degrees of effectiveness. They are described as follows: 1. Parotid gland protection with IMRT or 3-D conformal radiotherapy Overall, 3-D conformal radiotherapy cannot effectively prevent oral dryness, while IMRT can. The parotid gland receives sympathetic and parasympathetic innervation. Stimulation of sympathetic nerve will cause secretion of submandibular gland but not parotid gland; stimulation of parasympathetic nerve will cause secretion of all salivary glands. The mechanism by which cholinomimetic drugs relieve oral dryness may be the stimulation of residual salivary gland cell function, but while protecting the parotid gland leads to an irritative proliferation of glandular alveolar cells. It is more effective if the parotid gland is protected by concomitant radiotherapy. Oral administration of furfurylin 5mg Qid can relieve dry mouth symptoms. And it is safe to take for a long time with no obvious side effects. 3.Use radiotherapy protective agent-amphotericin Amphotericin is an organothiophosphate, and its activated metabolite WR-1065 can selectively protect normal tissues and reduce the toxic reactions of radiotherapy and chemotherapy. 4.Moving the healthy submandibular gland to the subchin area Many studies have reported that no oral dryness occurred in patients who moved the healthy submandibular gland to the subchin area (radiotherapy field). 5.Increase the number of muscarinic receptors The use of Zhengrui (cyclopentethione tablets) can relieve dry mouth by increasing the number of muscarinic receptors to achieve the effect of increasing the secretion of glands (such as salivary glands and lacrimal glands). 6.Other In addition, methods to prevent and treat dry mouth include: using saliva substitutes; acupuncture; using metal chelators, free radical scavengers or antioxidant enzymes before radiotherapy; and using transgenic technology.