Salivary gland disease
Blockage of thesubmandibular gland by asalivary stone with subsequent infection. Arrow marks pus coming out of the opening of the submandibular gland
Specialty	Gastroenterology,oral and maxillofacial surgery

Salivary gland diseases (SGDs) are multiple and varied in cause.^[1] There are three paired majorsalivary glands in humans: theparotid glands, thesubmandibular glands, and thesublingual glands. There are also about 800–1,000 minor salivary glands in themucosa of themouth. The parotid glands are in front of theears, one on side, and secrete mostlyseroussaliva, via theparotid ducts (Stenson ducts), into the mouth, usually opening roughly opposite thesecond upper molars. The submandibular gland ismedial to the angle of themandible, and it drains its mixture of serous andmucous saliva via the submandibular duct (Wharton duct) into the mouth, usually opening in a punctum in thefloor of mouth. The sublingual gland is below the tongue, on the floor of the mouth; it drains its mostly mucous saliva into the mouth via about 8–20 ducts, which open along the plica sublingualis, a fold of tissue under the tongue.^[2]

The function of the salivary glands is to secrete saliva, which has a lubricating function, which protects the mucosa of the mouth during eating and speaking.^[2] Saliva also containsdigestive enzymes (e.g. salivaryamylase), hasantimicrobial action, and acts as abuffer.^[3] Salivary-gland dysfunction occurs when salivary rates are reduced; this can causexerostomia (dry mouth).^[4]

Some disorders affecting the salivary glands are listed below. Some are more common than others, and they are considered according to asurgical sieve; but this list is not exhaustive.Sialadenitis is inflammation of a salivary gland, usually caused by infections, although there are other, less common causes of inflammation, such as irradiation, allergic reactions, and trauma.^[5]

Congenital disorders of the salivary glands are rare.^[5] They include:

• Aplasia
• Atresia
• Ectopic salivary gland tissue
• Stafne defect - an uncommon condition which some consider to be an anatomic variant rather than a true disease. It is thought to be created by an ectopic portion of salivary gland tissue which causes the bone of the mandible to remodel around the tissue, creating an apparentcyst like radiolucent area on radiographs. Classically, this lesion is discovered as a chance finding,^[6] since it causes no symptoms. It appears below theinferior alveolar nerve canal in theposterior region of the mandible.

Salivary gland dysfunction affects the flow, amount, or quality of saliva produced. A reduced salivation is termedhyposalivation. Hyposalivation often results in a dry mouth condition calledxerostomia, and this can causetooth decay due to the loss of the protective properties of saliva. In addition, the results of a study have suggested that hyposalivation could lead to acute respiratory infection.^[7] There are two potential reasons for increasing the incidence rate of this infection. First, reduced saliva secretion may impair the oral and airway mucosal surface as a physical barrier, which consequently enhances the adhesion and colonization of viruses. Second, this reduction may also impair the secretion of antimicrobial proteins and peptides.^[7] In saliva, there are many antiviral proteins and peptides, some of which can inhibit replication of viruses, especially coronavirus; these salivary proteins may also protect against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).^[8] Therefore, hyposalivation may be a risk factor for acute respiratory infection, including (COVID-19). However, further investigations are crucial to prove this hypothesis.^[8]

Hypersalivation is the overproduction of saliva and has many causes.^[9][10]

• Necrotizing sialometaplasia is a lesion that usually arises from a minor salivary gland on the palate. It is thought to be due to vascularinfarction of the salivary gland lobules. It is often mistaken fororal cancer, but the lesion is not neoplastic.^[2]

Infections involving the salivary glands can beviral orbacterial (or rarelyfungal).

• Mumps is the most common viral sialadenitis. It usually occurs in children and involves pain in front of the ear, swelling of the parotid,fever, chills, and headaches.^[2]
• Bacterial sialadenitis is usually caused by ascending organisms from the mouth. Risk factors include reduced salivary flow.
• Human immunodeficiency virus-associated salivary gland disease (HIV-SGD).^[1]

• Oral mucoceles are common, and are caused by rupture of a salivary gland duct and spillage ofmucin into the surrounding tissues. Usually, they are caused by trauma. Classically, a mucocele is bluish and fluctuant, and most commonly occurs on the lower lip.^[11]
• Ranula is a mucocele under the tongue. Ranulas may be larger than mucoceles at other sites; they are usually associated with the sublingual gland, and less often they arise from the submandibular gland or a minor salivary gland.^[11] Rarely, a ranula may descend into the neck rather than the mouth (plunging ranula). If small, the ranula may be left alone; if it is larger and causing symptoms, excision of the sublingual gland may be indicated.
• Nicotinic stomatitis is whitening of the hard palate byhyperkeratosis caused by the heat from smoking or from drinking hot liquids. This irritation also causes inflammation of the duct openings of the minor salivary glands of the palate, and they become dilated. This manifests as red patches or spots on a white background.^[12]

• Sjögren's syndrome
• Graft-versus-host disease

• Post-irradiation sialadenitis
• Sarcoidosis—there may beparotitis alone oruveoparotitis (inflammation of both the parotid and theuvea of the eyes), which occurs inHeerfordt's syndrome.
• Cheilitis glandularis—This is inflammation of the minor salivary glands, usually in the lower lip, eversion and swelling of the lip.^[11]
• Chronic sclerosing sialadenitis is a salivary gland manifestation ofIgG4-related disease.^[13][14]

• Frey's syndrome

• Salivary gland neoplasm

• 
  Relative incidence of parotid tumors.^[15]
• 
  Relative incidence of submandibular tumors.^[15]

Asalivary diverticulum (pluraldiverticuli) is a small pouch or out-pocketing of the duct system of a majorsalivary gland.^[16] Such diverticuli typically cause pooling of saliva and recurrentsialadenitis,^[17] especiallyparotitis.^[18] A diverticulum may also cause asialolith to form.^[19][20]The condition can be diagnosed bysialography.^[17] Affected individuals may "milk" the salivary gland to encourage flow of saliva through the duct.^[17]

• Sialolithiasis - although several possibly coexisting factors have been suggested to be involved in the formation of salivary stones, including altered acidity of saliva, reduced salivary flow rate, abnormal calcium metabolism and abnormalities in the sphincter mechanism of the duct opening, the exact cause in many cases is unknown.
• Sialadenosis (sialosis) is an uncommon, non-inflammatory, non-neoplastic, recurrent swelling of the salivary glands. The cause is hypothesized to be abnormalities of neurosecretory control. It may be associated withalcoholism.^[5][21][22]

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• Salivary gland pathology

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