Microbial profile of symptomatic pericoronitis lesions: a cross-sectional study

Abstract Objective: The microbial composition of pericoronitis (Pc) is still controversial; it is not yet clear if the microbial profile of these lesions is similar to the profile observed in periodontitis (Pd). Therefore, the aim of the present study was to describe the microbial profile of Pc lesions and compare it directly with that of subjects with Pd. Methodology: Subjects with Pc and Pd were selected, and subgingival biofilm samples were collected from (i) third molars with symptomatic Pc (Pc-T), (ii) contralateral third molars without Pc (Pc-C) and (iii) teeth with a probing depth >3 mm from subjects with Pd. Counts and proportions of 40 bacterial species were evaluated using a checkerboard DNA-DNA hybridization technique. Results: Twenty-six patients with Pc and 18 with Pd were included in the study. In general, higher levels of microorganisms were observed in Pd. Only Actinomyces oris and Eubacterium nodatum were present in higher mean counts in the Pc-T group in comparison with the Pc-C and Pd-C groups (p<0.05). The microbiota associated with Pc-T was similar to that found in Pc-C. Sites with Pc lesions had lower proportions of red complex in comparison with the Pd sites. Conclusion: The microbiota of Pc is very diverse, but these lesions harbour lower levels of periodontal pathogens than Pd.


Introduction
Pericoronitis (Pc) is an infectious condition involving the soft tissue around the crown of a partially erupted tooth. 1 Thus, a high prevalence of Pc during the eruption of primary and permanent dentition could be expected. However, this condition rarely occurs in primary dentition; it is mainly associated with the eruption of the mandibular third molars 2 and is more commonly reported in females. 3 Although Pc may affect the patient's quality of life because it is often followed by discomfort, pain, bleeding, halitosis or even trismus, this condition is often neglected in daily clinical practice. 1 Third-molar eruption normally occurs in people between 18 and 25 years old, but problems with the eruption process are frequently observed. 2 A study that evaluated 245 cases of Pc found 35% of these cases occurred in patients between 20 and 29 years old. The occlusal surface of the affected tooth is often covered by gingival tissue, which favors the accumulation of food and biofilm, promoting the development of an infectious process. 2 Vertically impacted molars are more likely to present Pc. 4 Severe cases have an associated risk of systemic dissemination of the infection. 5 Very few studies to date have analyzed the microbial composition associated with Pc. 2,[6][7][8][9][10][11] Overall, studies have shown that periodontal pathogens are common in third-molar periodontal sites in subjects without periodontal diseases. [9][10][11] Previous studies have demonstrated the presence of gramnegative anaerobes and mobile forms of spirochetes in periodontal sites with Pc, 6,7 and concluded that the composition of the biofilm associated with Pc seems to be similar to that found in periodontitis (Pd). [8][9][10] However, these studies evaluated only a few biofilm samples and microbial species 6,7 or were not Pc patients and Pd patients comparative studies, [8][9][10][11] which could preclude a complete understanding on the microbial profile of Pc. Therefore, this study aims to describe the microbial profile of Pc lesions and compare it directly with the microbial profile of subjects with Pd.

Methodology Study design and settings
This is a bicentric cross-sectional study with a control-to-case ratio of 0.7. This study was conducted   17 The significance of the differences between the groups was assessed using one-way ANOVA test. In addition, a t-test was used to determine significant differences between the pairs of groups. Adjustments for multiple comparisons were performed when the 40 bacterial species were evaluated simultaneously. 17 All the analyses of this study were conducted using a statistical program The microbiota associated with the Pc-T group was very similar to that found in Pc-C. Most of the bacterial species evaluated in the study were found in higher counts in the Pd-C group, and 20 of them were significantly higher in this group compared with the Pc-T group, including Actinomyces gerencseriae, The mean proportions of the microbial complexes in the different groups are described in Figure 3.
The red complex pathogens were higher in Pd-C than Pc-T and Pc-C groups (p<0.05). A similar trend was also observed for the green complex (p<0.05).
However, a tendency towards a higher proportion of yellow complex species in the PC groups was noticed (p=0.09).

Discussion
The results of this study showed Pc sites harbored a quite diverse microbiota; nonetheless, with a lower degree of dysbiosis than that observed in Pd lesions. study group. The species were ordered according to the microbial complexes described by Socransky, et al. 18 (1988). The significance of differences between groups was assessed using one-way ANOVA test. Different letters indicate significant differences between pairs of groups (t-test, p<0.05). Letters were color coded to indicate the different groups: green for Pc-C, red for Pc-T, and blue for Pd-C. Pc-C: Pericoronitis control group; Pc-T: Pericoronitis test group; Pd-C: Periodontitis control group J Appl Oral Sci. The main strength of this study is that, to the best of our knowledge, this is the first study to comprehensively assess the microbial composition of Pc lesions and to compare this profile to that found in Pd. One limitation of the study design is the relatively small sample size, due to the difficulty in selecting Pc cases in daily clinical practice. Furthermore, this study shows results for the 40 bacterial species proposed by Socransky, et al. 18 (1988) as it is well established that the periodontal microbiome comprises more taxa than those included in this group of bacterial species. 27 Nevertheless, this panel of species has been successfully used as a biological marker for many studies of periodontal disease risk and treatment. 28,29 A comprehensive study showed it covers approximately 60% of the bacterial genera present in the oral cavity. 30 Few studies have identified periodontal bacteria in pericoronitis samples, but it seems that pericoronal sites can harbor several pathogens. A recent study showed some periodontopathic bacteria and herpesviruses occurred concomitantly in pericoronitis  18 and Actinomyces species (blue). The significance of differences between groups was sought using the one-way ANOVA. The differences were only found for red and green complexes. Different letters indicate significant differences between pairs of groups (t-test, p<0.05). Pc-C: Pericoronitis control group; Pc-T: Pericoronitis test group; Pd-C: Periodontitis control group J Appl Oral Sci. 2020;28:e20190266 7/7 samples. 11 Such herpesviral-bacterial interaction could be an important feature of pericoronitis and should be further studied.
In conclusion, Pc microbiota is diverse, but these lesions harbor lower levels of periodontal pathogens than those of Pd.