We are pleased to introduce the collection Frontiers in Oral Health: Highlights in Oral Infections and Microbes 2021/2. This collection will welcome and showcase a selection of high impact articles authored by leaders in the field. The work presented here highlights the broad diversity of research performed across the Oral Infections and Microbes section, and aims to put a spotlight on the main areas of interest. This collection aims to further support Frontiers’ strong community by shining a spotlight on our authors' highly impactful research.

Karolinska Institutet (KI)

University Clinic of Dentistry, Medical University of Vienna

Queen Mary University of London

A collection illuminating breakthroughs and insights on Oral Infections and Microbes.

. The research topic of this summary covers the effectiveness of different irrigation protocols and solutions in reducing bacterial load in the root canal system of patients with apical periodontitis. Additionally, the effects of saliva from periodontally healthy and diseased subjects on the barrier function and inflammatory response in in vitro models of the oral epithelium are also discussed. <ul> <li>Dentistry diagnosis and treatment is based on clinical examination, but microbiological analysis of samples collected from the patient can provide supportive evidence.</li> <li>Activation methods provide significantly higher biofilm reduction than conventional needle irrigation methods.</li> <li>Saliva from both healthy and diseased subjects increased TER and induced IL-6 and IL-8 secretion in the in vitro oral epithelium models.</li> <li>Saliva from the periodontitis subjects contained significantly higher concentrations of M.</li> </ul>

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Frontiers in Oral Health

Oral Infections and Microbes

Frontiers in Oral Health: Highlights in Oral Infections and Microbes 2021/2

Editorial on the Research Topic <a href="https://www.frontiersin.org/research-topics/32353/highlights-in-oral-infections-and-microbes-20212">Highlights in oral infections and microbes 2021/2</a>Upon launching Frontiers in Oral Health, the inaugural editorial of the section Oral Infections and Microbes addressed the contemporary challenges of the field (<a href="#B1">1</a>). A series of Research Topics commissioned thereafter were summarized in the respective editorials (<a href="#B2">2</a>, <a href="#B3">3</a>). The Highlights in Oral Infections and Microbes 2021/2 Research Topic collection, detailed in this Editorial, was announced to showcase articles of contemporary importance in the field of oral microbiology and infection biology. A set of two articles of clinical and one of translational relevance were compiled and discussed further here. The first one brings into spotlight the value and potencies of laboratory microbiology in clinical diagnosis and treatment of oral diseases <a href="https://www.frontiersin.org/articles/10.3389/froh.2022.983991/full">Claesson et al. (2022)</a>, whereas the second article <a href="https://www.frontiersin.org/articles/10.3389/froh.2022.838043/full">Tonini et al. (2022)</a> and its associated corrigendum <a href="https://www.frontiersin.org/articles/10.3389/froh.2022.876265/full">Tonini et al. (2022)</a> discuss the effectiveness of various irrigating solutions and activation systems for root canal disinfection, raising the necessity for developing of standardized effective clinical protocols. The third article employed an in vitro model to evaluate the effects of saliva on oral epithelial barrier function <a href="https://www.frontiersin.org/articles/10.3389/froh.2021.815728/full">Roy et al. (2022)</a>.Conventional laboratory diagnostics can deliver supportive microbiological evidence to facilitate clinical decision-making <a href="https://www.frontiersin.org/articles/10.3389/froh.2022.983991/full">Claesson et al. (2022)</a>. Cultivation and molecular methods can be readily available in clinical laboratory environments. Periodontal, endodontic and odontogenic infections are identified as pathologies whose diagnosis or treatment could be assisted by clinical microbiology laboratory analysis for the benefit of the patient. Administration of antimicrobial agents, backed by prior microbiological analysis, can yield more predictable treatment outcomes in refractory or early occurring forms of periodontitis. Confirmation of a sterile root canal by means of a culture-negative sample during endodontic treatment may ensure the longevity of the treatment outcome. Antimicrobial susceptibility testing on samples obtained from odontogenic abscesses may guide the selection of the appropriate antimicrobial, in order to prevent further spread of the infection.Root canal system disinfection is an essential part of endodontic therapy, aiming to eliminate bacterial biofilm and prevent subsequent infection (<a href="#B4">4</a>). Traditionally used mechanical biofilm debridement does not always result in satisfactory bacteria elimination because of strong biofilm attachment to the surface, hiding bacteria in dentinal tubules, and the complex anatomy of the root canal system. A further possibility for root canal disinfection is the irrigation with disinfection solution, such as sodium hypochlorite or chlorhexidine. This procedure improves the elimination of bacteria but is not always sufficiently compelling. The effectiveness of the irrigation procedure could be further enhanced by using the activation system, which promotes the movement of the irrigating agent through the root canal system and allows better penetration within the biofilm. Tonini et al. analyzed the effectiveness of various irrigating solutions and activation systems in root canal disinfection using a systematic review tool <a href="https://www.frontiersin.org/articles/10.3389/froh.2022.838043/full">Tonini et al. (2022)</a>. The authors searched through different databases and found seven randomized controlled trials (RCT), which met the inclusion criteria and were included in the review. In four RCTs, only the irrigants in different combinations were used, whereas, in the other three RCTs, various activation techniques were additionally applied. Based on the data extraction and analysis, the authors concluded that using the activation technique is essential to root canal disinfection. Further, the application of sodium hypochlorite is indispensable in endodontic therapy. Finally, the authors emphasize the necessity of developing standardized clinical protocols for effective bacterial elimination from the root canal.There is a general lack of knowledge as regards the effect of saliva from subjects with periodontitis on the integrity of the epithelial barrier and the inflammatory response. The effects of unstimulated saliva from healthy and periodontitis subjects were compared with respect to these parameters using in vitro models of the oral epithelium <a href="https://www.frontiersin.org/articles/10.3389/froh.2021.815728/full">Roy et al. (2022)</a>. Saliva samples were analysed using an immunological multiplex assay to assess the levels of cytokines and metalloproteinases (MMPs) relevant to periodontitis. The impact of saliva on epithelial barrier integrity was assessed by monitoring transepithelial electrical resistance (TER) in an oral epithelium / keratinocyte model. Oral epithelial cells were also treated with saliva from both groups to determine their ability to induce the secretion of interleukin 6 (IL-6) and IL-8. Saliva from the periodontitis subjects contained significantly higher concentrations of MMP-8, MMP-9, IL-8, and chemokine ligand 1 compared healthy subjects. Saliva from both groups increased TER and induced IL-6 and IL-8 secretion to a similar extent. It is known that saliva from periodontitis subjects contains higher levels of pro-inflammatory mediators, MMPs, and bacteria-derived toxic products. It would be of interest to assess a wider range of such salivary biomarkers, including those of microbial origin, and determine any possible synergistic or inhibitory effects between these molecules.The authors have equally contributed to this editorial by summarizing the papers contained in the corresponding Research Topic. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Editorial: Highlights in oral infections and microbes 2021/2

Diagnosis and treatment in dentistry are based on clinical examination of the patients. Given that the major oral diseases are of microbial biofilm etiology, it can be expected that performing microbiological analysis on samples collected from the patient could deliver supportive evidence to facilitate the decision-making process by the clinician. Applicable microbiological methods range from microscopy, to culture, to molecular techniques, which can be performed easily within dedicated laboratories proximal to the clinics, such as ones in academic dental institutions. Periodontal and endodontic infections, along with odontogenic abscesses, have been identified as conditions in which applied clinical microbiology may be beneficial for the patient. Administration of antimicrobial agents, backed by microbiological analysis, can yield more predictable treatment outcomes in refractory or early-occurring forms of periodontitis. Confirming a sterile root canal using a culture-negative sample during endodontic treatment may ensure the longevity of its outcome and prevent secondary infections. Susceptibility testing of samples obtained from odontogenic abscesses may facilitate the selection of the appropriate antimicrobial treatment to prevent further spread of the infection.

Diagnosis and treatment in dentistry are based on clinical examination of the patients. Given that the major oral diseases are of microbial biofilm etiology, it can be expected that performing microbiological analysis on samples collected from the patient could deliver supportive evidence to facilitate the decision-making process by the clinician. Applicable microbiological methods range from microscopy, to culture, to molecular techniques, which can be performed easily within dedicated laboratories proximal to the clinics, such as ones in academic dental institutions. Periodontal and endodontic infections, along with odontogenic abscesses, have been identified as conditions in which applied clinical microbiology may be beneficial for the patient. Administration of antimicrobial agents, backed by microbiological analysis, can yield more predictable treatment outcomes in refractory or early-occurring forms of periodontitis. Confirming a sterile root canal using a culture-negative sample during endodontic treatment may ensure the longevity of its outcome and prevent secondary infections. Susceptibility testing of samples obtained from odontogenic abscesses may facilitate the selection of the appropriate antimicrobial treatment to prevent further spread of the infection.

Clinical laboratory diagnostics in dentistry: Application of microbiological methods

Corrigendum: Irrigating Solutions and Activation Methods Used in Clinical Endodontics: A Systematic Review

BackgroundEx vivo and in vitro studies have demonstrated the effectiveness of some irrigation protocols in reducing the bacterial load in the root canal system. However, standardized protocols have not yet been defined for the real clinical context due to many irrigation procedures available.</sec>ObjectiveTo evaluate the clinical endodontic protocols and limitations of irrigating solutions in the disinfection of the root canal system in patients with apical periodontitis.</sec>MethodsPubMed, Scopus, Embase, Web of Science, and Cochrane databases were searched for randomized controlled trials (RCT) published until January 2021. Hand searching was also performed. Studies focused on evaluating the effectiveness of irrigating solutions and/or irrigation activation methods in reducing the bacterial load in the root canal system were considered. The Cochrane risk-of-bias tool for randomized trials (RoB2) was used to assess the quality of the studies.</sec>ResultsFour hundred and twenty eight published articles were identified. After removing the duplicate studies and analyzing full texts, seven RCTs were selected. Two studies compared pure NaOCl with some combination of NaOCl with HEDP and MTAD. Two studies analyzed the antibacterial efficacy of NaOCl and chlorhexidine (CHX). Three studies compared conventional needle irrigation with different irrigation activation methods (PUI, XP-endo finisher, F-file activator, EndoVac activator). The review attained a satisfactory methodology. The main results of each included study were described.</sec>DiscussionActivation methods provide significantly higher biofilm reduction than conventional needle irrigation methods. Combinations of NaOCl with different chelating agents were ineffective in terms of antimicrobial, but it could potentially increase the risk of irrigant extrusion. However, the irrigating protocols were not carefully detailed, especially those regarding the irrigants application time or total volume. The existing literature lacks high-quality studies. The level of evidence is moderate.</sec>ConclusionsThe available data is too heterogeneous to compare and identify the superiority of specific valuable irrigation protocols in each clinical context. Application time, volume, and activation methods should be standardized to determine the optimal irrigating procedures to reduce the bacterial load and ensure higher predictability of the endodontic treatment.</sec>Systematic Review Registration(<ext-link ext-link-type="uri" xlink:href="https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=218555" xmlns:xlink="http://www.w3.org/1999/xlink">https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=218555</ext-link>), PROSPERO registration: <ext-link ext-link-type="uri" xlink:href="https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=218555" xmlns:xlink="http://www.w3.org/1999/xlink">CRD42020218555</ext-link>.</sec>

Background: Ex vivo and in vitro studies have demonstrated the effectiveness of some irrigation protocols in reducing the bacterial load in the root canal system. However, standardized protocols have not yet been defined for the real clinical context due to many irrigation procedures available.Objective: To evaluate the clinical endodontic protocols and limitations of irrigating solutions in the disinfection of the root canal system in patients with apical periodontitis.Methods: PubMed, Scopus, Embase, Web of Science, and Cochrane databases were searched for randomized controlled trials (RCT) published until January 2021. Hand searching was also performed. Studies focused on evaluating the effectiveness of irrigating solutions and/or irrigation activation methods in reducing the bacterial load in the root canal system were considered. The Cochrane risk-of-bias tool for randomized trials (RoB2) was used to assess the quality of the studies.Results: Four hundred and twenty eight published articles were identified. After removing the duplicate studies and analyzing full texts, seven RCTs were selected. Two studies compared pure NaOCl with some combination of NaOCl with HEDP and MTAD. Two studies analyzed the antibacterial efficacy of NaOCl and chlorhexidine (CHX). Three studies compared conventional needle irrigation with different irrigation activation methods (PUI, XP-endo finisher, F-file activator, EndoVac activator). The review attained a satisfactory methodology. The main results of each included study were described.Discussion: Activation methods provide significantly higher biofilm reduction than conventional needle irrigation methods. Combinations of NaOCl with different chelating agents were ineffective in terms of antimicrobial, but it could potentially increase the risk of irrigant extrusion. However, the irrigating protocols were not carefully detailed, especially those regarding the irrigants application time or total volume. The existing literature lacks high-quality studies. The level of evidence is moderate.Conclusions: The available data is too heterogeneous to compare and identify the superiority of specific valuable irrigation protocols in each clinical context. Application time, volume, and activation methods should be standardized to determine the optimal irrigating procedures to reduce the bacterial load and ensure higher predictability of the endodontic treatment.Systematic Review Registration: (<a href="https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=218555">https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=218555</a>), PROSPERO registration: <a href="https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=218555">CRD42020218555</a>.

Irrigating Solutions and Activation Methods Used in Clinical Endodontics: A Systematic Review

Background: Periodontitis is a multifactorial, bacteria-mediated chronic inflammatory disease that results in the progressive destruction of the tooth-supporting tissues. It is well-known that saliva from subjects suffering from this disease generally contains higher levels of pro-inflammatory mediators, matrix metalloproteinases (MMP), and bacteria-derived toxic products. The aim of this study was to investigate and compare the effects of saliva from periodontally healthy and diseased subjects on the barrier function and inflammatory response in in vitro models of the oral epithelium.Methods: Unstimulated saliva samples from two groups of subjects, one with a healthy periodontium (n = 12) and one with severe generalized periodontitis (n = 11), were filter-sterilized. All the saliva samples were analyzed using an immunological multiplex assay to determine the levels of various cytokines and MMPs relevant to periodontitis. The impact of saliva on epithelial barrier integrity was assessed by monitoring transepithelial electrical resistance (TER) in an oral epithelium model using the B11 keratinocyte cell line. GMSM-K oral epithelial cells were treated with saliva from both groups to determine their ability to induce the secretion of interleukin-6 (IL-6) and interleukin-8 (IL-8), as determined by an enzyme-linked immunosorbent assay (ELISA).Results: Saliva from the periodontitis subjects contained significantly higher concentrations of matrix metalloproteinase-8 (MMP-8), matrix metalloproteinase-9 (MMP-9), IL-8, and C-X-C motif chemokine ligand 1 (CXCL1) compared to saliva from the healthy subjects. Saliva from the healthy and periodontitis subjects affected cytokine secretion and TER in a similar manner. More specifically, saliva from both groups increased TER and induced IL-6 and IL-8 secretion in the in vitro oral epithelium models used.Conclusion: Independently of the presence or absence of periodontitis, saliva can increase the relative TER and the secretion of IL-6 and IL-8 in in vitro models of the oral epithelium.

Background: Periodontitis is a multifactorial, bacteria-mediated chronic inflammatory disease that results in the progressive destruction of the tooth-supporting tissues. It is well-known that saliva from subjects suffering from this disease generally contains higher levels of pro-inflammatory mediators, matrix metalloproteinases (MMP), and bacteria-derived toxic products. The aim of this study was to investigate and compare the effects of saliva from periodontally healthy and diseased subjects on the barrier function and inflammatory response in in vitro models of the oral epithelium.Methods: Unstimulated saliva samples from two groups of subjects, one with a healthy periodontium (n = 12) and one with severe generalized periodontitis (n = 11), were filter-sterilized. All the saliva samples were analyzed using an immunological multiplex assay to determine the levels of various cytokines and MMPs relevant to periodontitis. The impact of saliva on epithelial barrier integrity was assessed by monitoring transepithelial electrical resistance (TER) in an oral epithelium model using the B11 keratinocyte cell line. GMSM-K oral epithelial cells were treated with saliva from both groups to determine their ability to induce the secretion of interleukin-6 (IL-6) and interleukin-8 (IL-8), as determined by an enzyme-linked immunosorbent assay (ELISA).Results: Saliva from the periodontitis subjects contained significantly higher concentrations of matrix metalloproteinase-8 (MMP-8), matrix metalloproteinase-9 (MMP-9), IL-8, and C-X-C motif chemokine ligand 1 (CXCL1) compared to saliva from the healthy subjects. Saliva from the healthy and periodontitis subjects affected cytokine secretion and TER in a similar manner. More specifically, saliva from both groups increased TER and induced IL-6 and IL-8 secretion in the in vitro oral epithelium models used.Conclusion: Independently of the presence or absence of periodontitis, saliva can increase the relative TER and the secretion of IL-6 and IL-8 in in vitro models of the oral epithelium.

Effects of Saliva From Periodontally Healthy and Diseased Subjects on Barrier Function and the Inflammatory Response in in vitro Models of the Oral Epithelium