As the present study showed, the prevalence of caries was significantly greater in the group of children with a history of symptomatic COVID-19 infection than in the group of asymptomatic children. For permanent teeth, the symptomatic group was 71%, and the asymptomatic group was 59%. For primary teeth, the symptomatic group was 88%, and the asymptomatic group was 68%.
In the symptomatic group, the mean DMFT + deft was 5.9, which was evaluated by the WHO as high caries intensity, and in the asymptomatic group, it was 3.8, which was classified as moderate. In the symptomatic group, the mean S-OHI was 1.9, which was considered to indicate fair results, while in the asymptomatic group, the mean hygiene index slightly exceeded the norm (− 1.4). In the symptomatic group, the mean MGI = 0.92; in the asymptomatic group, the mean MGI = 0.5.6. Thus, in the symptomatic group, the means of all studied oral health indicators worsened; however, it was shown that a history of the symptomatic course of COVID-19 had a greater impact on caries intensity in the post-COVID population.
In the post-COVID-19 study population, the intensity of caries in primary teeth was greater (3.9) than the intensity of caries in permanent teeth (2.8). A similar trend was observed in the symptomatic and asymptomatic groups. Additionally, the prevalence of caries in primary teeth was greater (84%) than that in permanent teeth (74%). This can be explained by the older age of temporary teeth compared to permanent teeth and their anatomical and morphological features. These results are consistent with those of other studies in which the mean caries score for primary teeth in the post-COVID-19 pediatric population was 5.67, whereas it was 2.53 for permanent teeth. (Alghamdi et al., 2022).
The abundances of the microorganisms studied in this research (Staphylococcus aureus, Candida albicans, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Staphylococcus epidermalis) have been shown to increase abundantly in the saliva of our population; these microorganisms are pathogenic and conditionally pathogenic, but they are not considered specific causes of caries and periodontal diseases (Du et al., 2021; Rivas Caldas et al., 2015). However, their abundant growth significantly disrupts the microbial balance of the oral cavity; therefore, with the symptomatic course of COVID-19 infection, weakening of the body's general immune system may have a significant negative impact on oral health (Levinson, 2016). The presence of opportunistic oral infections caused by Candida albicans in symptomatic COVID-19 patients has been described in other studies. (Cuevas-Gonzalez et al., 2021).
In contrast to these studies, our study showed that, in a group of children with a history of symptomatic COVID-19 infection, the frequency of the five studied microorganism cultures increased, and oral hygiene was significantly worse, similar to other indicators, than in children with a history of asymptomatic COVID-19. However, this study does not allow us to explain in the symptomatic group what the initial trigger for the results obtained was the following: the symptomatic course of COVID-19 had a direct impact on changes in the salivary microbiome; conversely, the symptomatic course of infection aggravated oral hygiene, which led to changes in the salivary microbiome. In addition, our study cannot determine whether symptomatic COVID-19 causes impairment of oral health. To answer such questions and determine cause-and-effect relationships, additional in-depth studies are needed, which, in our case and in many other studies, is not possible due to the lack of a control group. (Kumar & Jat, 2023). Based on the logistic regression results, we can only say that in our population, a symptomatic course of COVID-19 infection is associated with worsening oral health.
In general, retrospective studies in the literature have shown that prepandemic children had significantly lower caries intensity and more frequent treatment than did those registered during the pandemic. (K. Moller, 2023), Lockdown and sedentarism, violation of nutrition and hygiene regime, and delay of planned dental visits had a significant impact on the oral health of children during the pandemic (Angelopoulou et al., 2023; Wdowiak-Szymanik et al., 2022).
In our study, 65.8% (n = 277) of the laboratory-confirmed patients had oral symptoms. Oral symptoms were almost equally distributed between the sexes. Similar results were obtained in a study in which a meta-analysis of 35 articles was conducted (Iranmanesh et al., 2021).
Among the oral symptoms, the most frequently reported were a decrease/change in taste (dysgeusia) of 26.1% (n = 110), which is considered to be the most recognized oral symptom of COVID-19. (Cuevas-Gonzalez et al., 2021; Iranmanesh et al., 2021). Additionally, smell disorders and an increase in plaque on the teeth were most often observed.
The impact of symptomatic COVID-19 on the severity of carious lesions on permanent and primary teeth was similar, and a slightly greater impact was observed for permanent teeth: DMFT (OR = 1.32; 95% CI = 1.15–1.52) and deft (OR = 1.22; 95% CI = 1.07–1.38). The symptomatic group had a 2.1-fold greater chance of having all five studied microbes (OR = 2.1 95% CI = 1.23–3.67) and a 3.4-fold greater chance of having impaired oral hygiene (OR = 3.4; 95% CI = 2.03–5.76) than did the asymptomatic group.
Additionally, the symptomatic course of COVID-19 affects periodontal health in MGI patients (OR = 2.31; 95% CI = 1.50–3.55). Thus, by comparing the means, ORs, and logistic regression results, we can conclude that the symptomatic course of COVID-19 infection is an additional risk factor that further worsens the microbial balance of oral saliva and, accordingly, the indicators of oral health.
According to the research methodology, the distribution of the beneficiaries included in the research according to the principle of random selection into groups (symptomatic/asymptomatic) markedly differed: symptomatic, 355 (82.32%); and asymptomatic, 66 (15.67%). A similar trend was observed in the literature review, where a meta-analysis of 48 studies was conducted in the pediatric population of all ages; it was observed that 20% of the children had an asymptomatic course, and the rest had a mild to moderate course. (Cui et al., 2021). The similar distribution in our population can be explained by the fact that in the country, state funding was used to test only those with a symptomatic history, which is a significant obstacle to the detection of asymptomatic, laboratory-confirmed children. Literature analysis also confirms that a lack of testing in asymptomatic children has also been reported in other countries. (Gao et al., 2021; Nikolopoulou & Maltezou, 2022).
The beneficiaries included in the study had an asymptomatic, mild to moderate course of infection. Children with a history of severe COVID-19 were not included in the selection, which is explained by the fact that severe COVID-19 infection is rare in the pediatric population. (Ludvigsson, 2020; Zhang et al., 2022). Based on the results of the present study, it is possible to hypothesize that in children with severe symptoms of COVID-19, a closer association between the symptomatic course of COVID-19 and oral health in the post-COVID-19 period is expected. The generation of such an idea allows us to recommend a similar study of diazine in the pediatric population with chronic diseases.
Importantly, the present study included clinical and laboratory data to confirm the screening results, and it was not based on subjective data from questionnaires. A scientific innovation is intraoral mobile photography of the beneficiaries conducted in parallel during the screening process.
The impossibility of a deeper microbiological study of oral microflora can be considered a limitation of this research. It should be noted that the PCR study of saliva would have given us the basis for a more detailed analysis and conclusions. However, since the research is not purely clinical and public health provides for budgetary studies aimed at the population, the researchers considered it relevant.