Introduction: COVID-19 has caused a wide range of symptomatology, including that present in the oral cavity. A new related syndrome is gaining importance: Long COVID. The aim of this work is to analyse the effect of SARS-CoV-2 infection at the oral level in subjects diagnosed with Long COVID, compared to acute infection.

Methods: A case-control study was conducted with 102 subjects recruited between 2021 and 2022, from whom 34 oral health variables and possible risk factors were obtained.

Results: Statistical analysis revealed that Long COVID subjects had significantly higher prevalence of: adenopathies, TMJ pain, pharyngeal irritation, xerostomia, fillings, dental absences and dental crowns, higher CAOM and CAOD index values and higher total dental symptoms. In addition, stress appeared as a risk factor; those patients with Long COVID who presented a higher level of stress (7.73 ± 2.02) were also those who suffered, to a greater extent, from xerostomia or bruxism, responsible for TMJ pain, also more prevalent in this group.

Conclusions: Long COVID causes oral manifestations related, some of them, to the fact that the oral cavity is a route of entry of the virus, such as mucosal irritation; others, related to its possible autoimmune nature, such as mucosal irritation; others, related to its possible autoimmune nature, such as xerostomia and, in the same way, others related to stress, reflected in the presence of bruxism. It is essential to develop protocols that improve both the early diagnosis and management of these patients in our clinics.

Key words: COVID-19; Long COVID; Mucosal irritation; Xerostomia; Adenopathies; Bruxism and stress.

The impact of the COVID-19 pandemic was profoundly transformative for humanity, affecting every aspect of our lives. When, at the end of 2019, the SARS-CoV-2 virus altered its evolution to make the leap to the human host, no one could have imagined the repercussions this would entail. Since the first cases were identified at the end of 2019, the virus spread rapidly worldwide, generating an unprecedented health crisis.

This is a highly contagious virus that has raised significant questions regarding community transmission processes, the pathogenesis of infections, and, above all, its involvement in the immune response. The latter was the catalyst for investigations that revealed how COVID-19 can exacerbate pre-existing autoimmune diseases and may trigger an exaggerated immune response in certain patients, thereby worsening the clinical picture¹.

Indeed, a proportion of infected individuals continue to manifest disease-related symptoms, of variable intensity, persisting over time. This proportion varies depending on the state of chronic inflammation prior to infection and the pre-existing diseases of each individual, although data published by the World Health Organization, as of March 2023, appear to indicate that approximately 10% to 20% of the population experiences medium- and long-term effects following the initial infection. These cases have been classified within a new category termed ‘persistent COVID syndrome’, ‘post-COVID syndrome’, ‘post COVID-19 condition’ or ‘Long COVID’.
Long COVID can affect individuals of any age, sex, or medical condition and encompasses a wide range of clinical manifestations, which may involve various systems, including the cardiovascular, respiratory, and nervous systems².

In general, it is believed that the underlying pathological mechanisms of Long COVID may be related to a state of chronic inflammation and tissue damage induced by the virus. These processes may generate an exaggerated residual inflammatory response, which can result in organ damage and prolong the recovery of patients. Furthermore, the immune response may account for Long COVID, as some patients have demonstrated a hyperactive and sustained immune response following infection, which may result in chronic inflammation and persistent organ damage³.

Within the context of the pandemic, mechanisms related to stress cannot be disregarded. It should be understood, in principle, as a natural physiological and psychological response of the organism to adverse situations, constituting a natural protective mechanism. However, when such stress is prolonged, it may have detrimental effects on health⁴. In recent years, it has been demonstrated that chronic stress can affect the immune system and predispose individuals to the development of infectious diseases. This is attributable to the fact that stress can alter the immune response, modifying its capacity to combat infectious agents and thereby diminishing its competence to protect against diseases⁵.

Finally, COVID-19 has caused a wide range of symptoms and complications across various bodily systems. Among others, a wide variety of oral symptoms have been reported, which must be addressed to ensure appropriate diagnosis and treatment of these patients⁶. However, it is important to emphasise that these oral manifestations associated with COVID-19 are not specific to this disease, but may also occur in other conditions, both infectious and non-infectious. They primarily present in the following forms:

• Oral lesions resembling recurrent aphthous stomatitis: these may be found in various areas within the oral cavity, including the buccal mucosa, lips, and palate⁷.
* Oral ulcers: similar to those observed in other viral infections such as herpes simplex virus (HSV) and Epstein-Barr virus⁸, and have even been considered an initial sign of COVID-19⁹.
• Lesions on the tongue: similar to geographic tongue¹⁰.
• Necrotising ulcerative gingivitis: more common in patients with COVID-19 than in individuals without the disease¹¹.
Alterations in taste perception (dysgeusia): as well as anosmia, related to the sense of smell. Patients infected with COVID-19 may experience a reduction in their sense of taste, alterations in flavour, or a complete loss thereof. The majority of patients exhibit these changes temporarily; however, some may experience this symptom as a persistent long-term effect following recovery from the disease¹².
• Others: xerostomia, halitosis, vesiculobullous lesions, fissures or depapillation of the tongue, and oral candidiasis¹³.

All these manifestations may be of concern to patients with COVID-19 and to dental health professionals, as they could indicate an active infection and the need for appropriate follow-up. Studies have demonstrated that SARS-CoV-2 is present in the saliva of infected patients from the early stages of infection and has also been detected in samples obtained from the tonsils, suggesting that the salivary glands may also serve as a potential reservoir for the virus. This could be due to the high expression of ACE2 receptors in the salivary glands¹⁴, a demonstrated entry point for the virus into cells. It has also been proposed that oral manifestations associated with COVID-19 may be related to dysfunction of the immune system¹⁵.

However, we found limited literature on oral health in patients with long COVID and the implications of the pandemic for the general population in this respect. Therefore, the objective of this study was to comprehensively evaluate the effect of SARS-CoV-2 infection on oral health status and, more specifically, its condition in individuals who developed long COVID.