Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) the cause of the pandemic known as COVID-19, affects different organs and systems (lungs, heart, blood vessels, kidney, intestine, eyes, brain, etc.), and the oral cavity is no exception.  

SARS-CoV-2 uses the angiotensin converting enzyme 2 (ACE2) receptor to infect human cells; ACE2 is found not only in the lungs, liver, kidney, gastrointestinal tract, capillary endothelium, but has also been found in the oral mucosa, especially on the back of the tongue, floor of the mouth, in the major (submandibular, parotid and sublingual) and minor salivary glands and also in the cells of the buccal and gingival epithelium (1,2,3). 

The effect of SARS-CoV-2 on the salivary glands can cause a decrease in the flow of saliva and can affect its composition. As a consequence, dysgeusia (taste disorders), xerostomia, and halitosis develop (3, 4).  

The first manifestations in patients infected by COVID-19 are reported to be alteration or loss of taste in 38% and xerostomia with a prevalence between 30% to 60% (3,4,5). In some cases, the prevalence of xerostomia is higher than or equal to taste alteration (3).  

Furthermore, xerostomia can last up to 8 months after recovery from SARS-CoV-2 infection due to the functional impairment of the acinar cells of the salivary glands, which are replaced within approximately 6 months (3).   

Xerostomia in patients affected by COVID-19, or post COVID-19 (3,4) may be caused by any of the following: 

• Hyposalivation, caused by impaired salivary gland function.  
• Sialadenitis. Prolonged repair of inflammatory lesions produced by SARS-CoV-2 on the salivary glands could cause chronic sialadenitis, and in turn, persistent xerostomia.
• Medication used to treat COVID-19 infection.  
• Serum zinc deficiency, observed in 85.7% of patients with severe impairment and in 13.6% of patients with mild to moderate impairment. It is associated with the reduction in salivary secretion by the salivary glands (parotid and submandibular).
• Neuropathy of the cranial nerves:  SARS-CoV-2 causes neuropathy in the facial, glossopharyngeal and trigeminal cranial nerves, which in turn is related to salivary reflex and the sense of taste, and therefore, their impairment induces xerostomia and loss of sense of taste.  
• Comorbidities, such as: diabetes mellitus, high blood pressure, chronic lung diseases, thyroid diseases, and chronic liver diseases. 

Furthermore, xerostomia has also occurred in non-COVID-19 patients, due to the frequent use of masks and protective screens, since these promote mouth breathing instead of nasal breathing, which contributes to increased dry mouth. 

Xerostomia has negative effects on the oral cavity and leads to the reduced quality of life of those affected, as it can cause: difficulty in swallowing and speaking, the need to drink water frequently, a dry mouth sensation, a burning sensation on the tongue and a persistent feeling of bad taste in the mouth (dysgeusia) (6). 

Similarly, it also negatively affects oral health, by increasing the risk of tooth decay, periodontal disease, tooth sensitivity, halitosis and oral infections.  

Xerostomia can be treated with saliva stimulants, moisturisers, or salivary gel substitutes. When used daily, these products help to moisturise the oral cavity and come in different forms: toothpaste, mouthwash, tablets, gums and spray. Additionally, it is important to reinforce oral hygiene techniques.  

It is important in oral hygiene products not to use abrasives or products with alcohol, as these can enhance the negative effects of xerostomia.  

As dental health professionals we have an important role in the prevention and treatment of the effects of COVID-19 on the oral cavity, including xerostomia.