On the dynamics of root canal infections-what we understand and what we don't

Oxygen Self-Supplied Nanoplatform for Enhanced Photodynamic Therapy against Enterococcus Faecalis within Root Canals

The successful treatment of persistent and recurrent endodontic infections hinges upon the eradication of residual microorganisms within the root canal system, which urgently needs novel drugs to deliver potent yet gentle antimicrobial effects. Antibacterial photodynamic therapy (aPDT) is a promising tool for root canal infection management. Nevertheless, the hypoxic microenvironment within the root canal system significantly limits the efficacy of this treatment. Herein, a nanohybrid drug, Ce6/CaO2/ZIF-8@polyethylenimine (PEI), is developed using a bottom-up strategy to self-supply oxygen for enhanced aPDT. PEI provides a positively charged surface, which enables precise targeting of bacteria. CaO2 reacts with H2O to generate O2, which alleviates the hypoxia in the root canal and serves as a substrate for Ce6 under 660 nm laser irradiation, leading to the successful eradication of planktonic Enterococcus faecalis (E. faecalis) and biofilm in vitro and, moreover, the effective elimination of mature E. faecalis biofilm in situ within the root canal system. This smart design offers a viable alternative for mitigating hypoxia within the root canal system to overcome the restricted efficacy of photosensitizers, providing an exciting prospect for the clinical management of persistent endodontic infection.

Systemic Antibiotic Use in Acute Irreversible Pulpitis: Evaluating Clinical Practices and Molecular Insights

This scoping review systematically evaluates the use of systemic antibiotics in treating acute irreversible pulpitis, integrating clinical practice patterns with recent molecular insights. We analyzed clinical evidence on antibiotic prescription trends among dental professionals and examined molecular research advancements in relation to pulpitis. This review is intended to bridge the gap between clinical practice and molecular research, guiding more evidence-based approaches to treating acute irreversible pulpitis. Electronic databases were searched for relevant articles published in English based on the objective of the review. A second search using all identified keywords and index terms was undertaken across all the included databases. In addition, a reference list of identified articles was searched. Studies including original research, systematic reviews, meta-analyses, clinical trials, and observational and retrospective studies, all written in English and published from 2010 onwards, were included, and an analysis of the text words contained in the titles and abstracts of the retrieved papers and of the index terms used to describe the articles was performed. A total of N = 53 articles were selected. Altogether, N = 43 (76.79%) articles were cross-sectional studies, N = 4 (11.11%) were systematic reviews, and N = 3 (5.36%) were guidelines. The most frequent level of evidence was level VI (N = 43 (76.79%). The mean percentage of dentists who prescribed antibiotics to treat acute irreversible pulpitis was 23.89 ± 23.74% (range: 0.05-75.7). Similarly, for specialists, it was 22.41 ± 15.64 (range 2.2-50.4), and the percentage for undergraduates was 17.52 ± 20.59 (range 0-62.6). The significant developments in research models for pulpitis research and the characterisation of biomarkers have led to better management strategies. Concurrently, significant advancements in molecular research provide new understandings of pulpitis, suggesting alternative therapeutic approaches. Although there are guidelines available, increased rates of antibiotic prescription are still prevalent around the globe.

Profiling Antibiotic Susceptibility among Distinct Enterococcus faecalis Isolates from Dental Root Canals

Enterococcus faecalis, a leading multi-resistant nosocomial pathogen, is also the most frequently retrieved species from persistently infected dental root canals, suggesting that the oral cavity is a possible reservoir for resistant strains. However, antimicrobial susceptibility testing (AST) for oral enterococci remains scarce. Here, we examined the AST profiles of 37 E. faecalis strains, including thirty-four endodontic isolates, two vanA-type vancomycin-resistant isolates, and the reference strain ATCC-29212. Using Etest gradient strips and established EUCAST standards, we determined minimum inhibitory concentrations (MICs) for amoxicillin, vancomycin, clindamycin, tigecycline, linezolid, and daptomycin. Results revealed that most endodontic isolates were susceptible to amoxicillin and vancomycin, with varying levels of intrinsic resistance to clindamycin. Isolates exceeding the clindamycin MIC of the ATCC-29212 strain were further tested against last-resort antibiotics, with 7/27 exhibiting MICs matching the susceptibility breakpoint for tigecycline, and 1/27 reaching that of linezolid. Both vanA isolates confirmed vancomycin resistance and demonstrated resistance to tigecycline. In conclusion, while most endodontic isolates remained susceptible to first-line antibiotics, several displayed marked intrinsic clindamycin resistance, and MICs matched tigecycline's breakpoint. The discovery of tigecycline resistance in vanA isolates highlights the propensity of clinical clone clusters to acquire multidrug resistance. Our results emphasize the importance of implementing AST strategies in dental practices for continued resistance surveillance.

Real-time optical detection of endodontic infection using bacterial autofluorescence

OBJECTIVES

For successful root canal treatment (RCT), it is essential to objectively assess the presence and activity of bacteria in the root canal system. However, current methods rely on subjective observations of root canal exudates. This study aimed to confirm whether real-time optical detection using bacterial autofluorescence can evaluate endodontic infection status by assessing the red fluorescence (RF) detected from root canal exudates.

METHODS

During RCT, endodontic paper points were used to collect root canal exudates scored using conventional organoleptic tests to assess the severity of root canal infections. RF on the paper points was assessed using quantitative light-induced fluorescence (QLF) technology. RF intensity and area from the paper points were quantified, and their correlations with infection severity were assessed using their organoleptic scores. The oral microbiome composition of RF samples was compared with non-red fluorescent (non-RF) samples.

RESULTS

The RF detection rate was nil and >98% in the non-infectious and severe groups. The RF intensity and area significantly increased with infection severity (p<0.001) and showed strong correlations with organoleptic scores (r=0.72, 0.82, respectively). The diagnostic accuracy for detecting root canal infection using RF intensity was good to excellent (AUC = 0.81-0.95) and increased with infection severity. The microbial diversity of the RF samples was significantly lower than that of the non-RF samples. Gram-negative anaerobic bacteria such as Prevotella and Porphyromonas were more predominant in RF samples.

CONCLUSIONS

Optical detection using bacterial autofluorescence can objectively evaluate endodontic infection status in real-time by assessing the RF of endodontic root canal exudates.

CLINICAL SIGNIFICANCE

This real-time optical technology can be utilised to detect endodontic bacterial infection without conventional incubation, allowing clinicians to determine the endpoint of chemomechanical debridement and increase the positive outcomes of RCTs.

Dual effectiveness of a novel all-in-one endodontic irrigating solution in antibiofilm activity and smear layer removal

The continuous destruction of dental hard tissues increases the risk of bacterial invasion, which leads to pulp infections. Irrigation is critical for successful root canal treatment in terms of infection control. However, no single irrigant covers all of the functions demanded, including antibiofilm and tissue-dissolving activities. The aim of this study was to investigate the antimicrobial properties of Triton, an all-in-one irrigant, on Enterococcus faecalis and multispecies oral biofilms in dentin canals, as well as its ability to remove the smear layer. Dentin blocks (192 specimens) were prepared from single-root human teeth and then assigned to 48 groups (24 groups for each biofilm type). Serial centrifugation was used for bacterial introduction into dentinal tubules. After 3 weeks, half of the specimens were created a uniform smear layer. The following treatments were applied: short time (separate): Triton, 6% NaOCl, 2% NaOCl, and water (all for 3 min); short time (combined): Triton (3 + 1 min), 6% NaOCl +17% EDTA (3 + 1 or 2 + 1 min), and 2% NaOCl +17% EDTA (3 + 1 min); and long time: Triton (3 + 3 min), 6% NaOCl (5 min), 6% NaOCl +17% EDTA (5 + 1 min), and water (3 + 3 min). Confocal laser scanning microscopy and scanning electron microscopy were employed to examine the antimicrobial activity and smear layer removal, respectively. The results revealed that despite the absence or presence of the smear layer, Triton (3 + 3 min) showed the highest killing for both tested biofilms (61.53%-72.22%) among all groups (p < 0.05). Furthermore, the smear layer was removed by Triton after 3 + 3 min, exposing open dentin canals. These findings demonstrated that Triton can provide dual benefits of antibiofilm and smear layer removal capabilities simultaneously, indicating a simplified and effective strategy for application in root canal treatment.

Nociceptor-Macrophage Interactions in Apical Periodontitis: How Biomolecules Link Inflammation with Pain

Periradicular tissues have a rich supply of peripheral afferent neurons, also known as nociceptive neurons, originating from the trigeminal nerve. While their primary function is to relay pain signals to the brain, these are known to be involved in modulating innate and adaptive immunity by initiating neurogenic inflammation (NI). Studies have investigated neuroanatomy and measured the levels of biomolecules such as cytokines and neuropeptides in human saliva, gingival crevicular fluid, or blood/serum samples in apical periodontitis (AP) to validate the possible role of trigeminal nociceptors in inflammation and tissue regeneration. However, the contributions of nociceptors and the mechanisms involved in the neuro-immune interactions in AP are not fully understood. This narrative review addresses the complex biomolecular interactions of trigeminal nociceptors with macrophages, the effector cells of the innate immune system, in the clinical manifestations of AP.

Root Canal Infection and Its Impact on the Oral Cavity Microenvironment in the Context of Immune System Disorders in Selected Diseases: A Narrative Review

The oral cavity has a specific microenvironment, and structures such as teeth are constantly exposed to chemical and biological factors. Although the structure of the teeth is permanent, due to exposure of the pulp and root canal system, trauma can have severe consequences and cause the development of local inflammation caused by external and opportunistic pathogens. Long-term inflammation can affect not only the local pulp and periodontal tissues but also the functioning of the immune system, which can trigger a systemic reaction. This literature review presents the current knowledge on root canal infections and their impact on the oral microenvironment in the context of immune system disorders in selected diseases. The result of the analysis of the literature is the statement that periodontal-disease-caused inflammation in the oral cavity may affect the development and progression of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, or Sjogren's syndrome, as well as affecting the faster progression of conditions in which inflammation occurs such as, among others, chronic kidney disease or inflammatory bowel disease.

The presence of Enterococcus faecalis in saliva as a risk factor for endodontic infection

Aim

The aim of the present study was to investigate and correlate the prevalence of Enterococcus faecalis in saliva and in root canals with different pulpal and periapical conditions.

Methodology

Sixty-seven patients were divided into five groups based on pulpal and periapical tissue status: healthy vital teeth (HVT, n=7), healthy treated teeth without lesion (HTT, n=9), irreversible pulpitis (IP, n=13), necrosis (N, n=18), and post-treatment apical periodontitis (PTAP, n=20). Saliva, rubber dam, sterility control and pre-treatment root canal samples were collected and microbiologically processed by culture method. The phylogenetic relationship of E. faecalis isolates collected from root canals and saliva were investigated by whole genome sequencing. Fisher’s exact test was used to correlate the presence of E. faecalis in root canals or saliva with clinical and/or radiographic findings. Linear/logistic regression analyses were performed to establish the relationship between the presence of E. faecalis in root canals, saliva, and the status of periapical tissues.

Results

E. faecalis was found in 18 root canal and saliva samples. E. faecalis root canal isolates were recovered with the highest frequency from post-treatment apical periodontitis. The occurrence of E. faecalis in saliva was strongly associated with its detection in the root canals (P &lt; 0.001). The pretreatment presence of E. faecalis in root canals was associated with significantly higher odds of having periapical lesions (OR=11.03; 95% CI, 1.27-95.70; p &lt; 0.05). Saliva and root canal isolates from the same patient were highly correlated at the phylogenetic level (Jaccard index &gt;0.95).

Conclusion

This pilot study confirms the role of E. faecalis in developing peri-radicular lesions in secondary endodontic infections and suggests that saliva could be the main source of infection. Further studies are needed to investigate the exact origin of this bacteria and its true role in the pathogenesis of secondary/persistent endodontic infections.

SEM analysis of the endodontic cavity wall after removal of restorative materials used as temporary restoration

AIM

The aim of the present in vitro study was to analyze the endodontic cavity walls for presence of remnants of conventional glass ionomer cement and flowable light cure composite used as temporary restorative materials of endodontically treated teeth. The dentine surface of the access cavity was observed with scanning electron microscopy after the final removal of the temporary restoration using high-speed turbine and diamond bur or ultrasonic device and diamond tip.

Clinical laboratory diagnostics in dentistry: Application of microbiological methods

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.

Alternative Antibiotics in Dentistry: Antimicrobial Peptides

The rise of antibiotic resistant bacteria due to overuse and misuse of antibiotics in medicine and dentistry is a growing concern. New approaches are needed to combat antibiotic resistant (AR) bacterial infections. There are a number of methods available and in development to address AR infections. Dentists conventionally use chemicals such as chlorohexidine and calcium hydroxide to kill oral bacteria, with many groups recently developing more biocompatible antimicrobial peptides (AMPs) for use in the oral cavity. AMPs are promising candidates in the treatment of (oral) infections. Also known as host defense peptides, AMPs have been isolated from animals across all kingdoms of life and play an integral role in the innate immunity of both prokaryotic and eukaryotic organisms by responding to pathogens. Despite progress over the last four decades, there are only a few AMPs approved for clinical use. This review summarizes an Introduction to Oral Microbiome and Oral Infections, Traditional Antibiotics and Alternatives & Antimicrobial Peptides. There is a focus on cationic AMP characteristics and mechanisms of actions, and an overview of animal-derived natural and synthetic AMPs, as well as observed microbial resistance.

Electrospun Nanofiber Films Suppress Inflammation In Vitro and Eradicate Endodontic Bacterial Infection in an E. faecalis-Infected Ex Vivo Human Tooth Culture Model

Treatment failure of endodontic infections and their concurrent inflammations is commonly associated with microbial persistence and reinfection, also stemming from the anatomical restrictions of the root canal system. Aiming to address the shortcomings of current treatment options, a fast-disintegrating nanofibrous film was developed for the intracanal coadministration of an antimicrobial (ZnO nanoparticles) and an anti-inflammatory (ketoprofen) agent. The electrospun films were fabricated based on polymers that dissolve rapidly to constitute the actives readily available at the site of action, aiming to eliminate both microbial infection and inflammation. The anti-inflammatory potency of the nanofiber films was assessed in an in vitro model of lipopolysaccharide (LPS)-stimulated RAW 264.7 cells after confirming their biocompatibility in the same cell line. The nanofiber films were found effective against Enterococcus faecalis, one of the most prominent pathogens inside the root canal space, both in vitro and ex vivo using a human tooth model experimentally infected with E. faecalis. The physical properties and antibacterial and anti-inflammatory potency of the proposed electrospun nanofiber films constitute a promising therapeutic module in the endodontic therapy of nonvital infected teeth. All manuscripts must be accompanied by an abstract. The abstract should briefly state the problem or purpose of the research, indicate the theoretical or experimental plan used, summarize the principal findings, and point out major conclusions.

Microbiological Aspects of Root Canal Infections and Disinfection Strategies: An Update Review on the Current Knowledge and Challenges

The oral cavity is the habitat of several hundreds of microbial taxa that have evolved to coexist in multispecies communities in this unique ecosystem. By contrast, the internal tissue of the tooth, i.e., the dental pulp, is a physiologically sterile connective tissue in which any microbial invasion is a pathological sign. It results in inflammation of the pulp tissue and eventually to pulp death and spread of inflammation/infection to the periradicular tissues. Over the past few decades, substantial emphasis has been placed on understanding the pathobiology of root canal infections, including the microbial composition, biofilm biology and host responses to infections. To develop clinically effective treatment regimens as well as preventive therapies, such extensive understanding is necessary. Rather surprisingly, despite the definitive realization that root canal infections are biofilm mediated, clinical strategies have been focused more on preparing canals to radiographically impeccable levels, while much is left desired on the debridement of these complex root canal systems. Hence, solely focusing on "canal shaping" largely misses the point of endodontic treatment as the current understanding of the microbial aetiopathogenesis of apical periodontitis calls for the emphasis to be placed on "canal cleaning" and chemo-mechanical disinfection. In this review, we dissect in great detail, the current knowledge on the root canal microbiome, both in terms of its composition and functional characteristics. We also describe the challenges in root canal disinfection and the novel strategies that attempt to address this challenge. Finally, we provide some critical pointers for areas of future research, which will serve as an important area for consideration in Frontiers in Oral Health.

Polymicrobial synergy stimulates Porphyromonas gingivalis survival and gingipain expression in a multi-species subgingival community

Background

Dysbiosis in subgingival microbial communities, resulting from increased inflammatory transudate from the gingival tissues, is an important factor in initiation and development of periodontitis. Dysbiotic communities are characterized by increased numbers of bacteria that exploit the serum-like transudate for nutrients, giving rise to a proteolytic community phenotype. Here we investigate the contribution of interactions between members of a sub-gingival community to survival and development of virulence in a serum environment—modelling that in the subgingival pocket.

Methods

Growth and proteolytic activity of three Porphyromonas gingivalis strains in nutrient broth or a serum environment were assessed using A₆₀₀ and a fluorescent protease substrate, respectively. Adherence of P. gingivalis strains to serum-coated surfaces was studied with confocal microscopy and 2D-gel electrophoresis of bacterial supernatants used to investigate extracellular proteins. A model multi-species sub-gingival community containing Fusobacterium nucleatum, Streptococcus constellatus, Parvimonas micra with wild type or isogenic mutants of P. gingivalis was then created and growth and proteolytic activity in serum assessed as above. Community composition over time was monitored using culture techniques and qPCR.

Results

The P. gingivalis strains showed different growth rates in nutrient broth related to the level of proteolytic activity (largely gingipains) in the cultures. Despite being able to adhere to serum-coated surfaces, none of the strains was able to grow alone in a serum environment. Together in the subgingival consortium however, all the included species were able to grow in the serum environment and the community adopted a proteolytic phenotype. Inclusion of P. gingivalis strains lacking gingipains in the consortium revealed that community growth was facilitated by Rgp gingipain from P. gingivalis.

Conclusions

In the multi-species consortium, growth was facilitated by the wild-type and Rgp-expressing strains of P. gingivalis, suggesting that Rgp is involved in delivery of nutrients to the whole community through degradation of complex protein substrates in serum. Whereas they are constitutively expressed by P. gingivalis in nutrient broth, gingipain expression in the model periodontal pocket environment (serum) appeared to be orchestrated through signaling to P. gingivalis from other members of the community, a phenomenon which then promoted growth of the whole community.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01971-9.

Patients with persistent idiopathic dentoalveolar pain in dental practice

Aim

To assess whether persistent idiopathic dentoalveolar pain (PIDAP), a diagnosis of exclusion, exhibits common features that can facilitate its diagnosis. PIDAP is defined by the International Classification of Orofacial Pain (ICOP 6.3.) as ‘Persistent unilateral intraoral dentoalveolar pain, rarely occurring in multiple sites, with variable features but recurring daily for more than 2 h per day for more than 3 months, in the absence of any preceding causative event’.

Methodology

In this observational study, participants fulfilling the new ICOP diagnostic criteria of PIDAP were included, covering 16 years of consecutive data. A systematic, retrospective assessment of patients utilizing the new PIDAP criteria on complaints of chronic tooth pain in a referral‐based endodontic practice was undertaken. Non‐idiopathic cases were excluded on the basis of clinical and radiologic findings. A modified neuropathic pain questionnaire was used to describe the painful sensations. Furthermore, allodynia in the periodontal space and sensory changes in the oral mucosa were assessed using a periodontal probe.

Results

Amongst the 160 patients assessed, 78 (63 women) fulfilled the strict PIDAP criteria. Pain history of PIDAP included no nocturnal awakening (85%) and a ‘pulling/dragging’ pain quality (59%). In 69% of the patients with PIDAP, pain was associated with a root filled tooth at the same site. In 14% of the cases, no endodontic treatment was performed in the affected quadrant. Mechanical allodynia in the gingival sulcus was observed in 91% of patients with painful teeth or implants.

Conclusions

In this observational study, PIDAP mainly affected females and was associated with undisturbed sleep and periodontal allodynia.

A critical analysis of research methods to study clinical molecular biomarkers in Endodontic research

The authors of this narrative review aimed to address various experimental methods and make recommendations for how research should move forward in the context of studying biomarkers in clinical Endodontic research. The approach adopted is exemplified using two prominent clinical problems, namely (a) the ‘reversible’ versus ‘irreversible’ pulpitis conundrum and (b) persistent idiopathic dentoalveolar pain (PIDAP). Pulpitis under deep caries or dentinal cracks is understood from a histological perspective, but clinical assessment tools to indicate irreversibly inflamed aspects of the dental pulp are elusive. PIDAP, on the other hand, is a diagnosis of exclusion; its pathophysiology is complex and not understood sufficiently to avoid unnecessary dental treatments. This review addresses how diagnostic biomarkers could further our understanding of those and other clinical problems, and how issues can be tackled from a methodological point of view. Hence, different methodological approaches to identify suitable diagnostic biomarker(s) or use known biomarkers are presented. The importance of asking a relevant research question, collecting the most suitable fluid and using the ideal collection vehicle for the research question under investigation is discussed based on the defined clinical problems.

Interrelationship between the Microbial Communities of the Root Canals and Periodontal Pockets in Combined Endodontic-Periodontal Diseases

Periodontal and Endodontic diseases are biofilm-related diseases. The presence of microorganisms in root canals (RCs) and the complex microbiota of periodontal pockets (PPs) contribute to the development of endodontic-periodontal diseases. This study performed a systemic analysis using state-of-the-art sequence data to assess the microbial composition of infected RCs and PPs to further assess the microbiota and verify the possibility of cross-infection between these sites. The microbiomes of these combined diseases were examined with a focus on the V3-V4 hypervariable region of the 16S rRNA gene. The number of species in PP was higher than in RC, and there was a predominance of obligate anaerobes and gram-negative bacteria. In the RCs, the genera Enterococcus, Parvimonas, Stomatobaculum predominated, in contrast, the PPs revealed a predominance of Enterococcus, Parvimonas, Stomatobaculum, Peptostreptococcus and Mogibacterium. The RC and PP microbiome was not similar with regards to the sharing of OTUs for phyla and genera (8 and 67, respectively). The evaluation of molecular markers revealed a large number of markers for resistance to antibiotics of the carbapenem and beta-lactam type (broad spectrum). Another relevant finding of this study was the markers related to systemic diseases related to cardiac muscle and rheumatology, among others. In conclusion, the RC microbiota was less complex and diverse than PP. Interactions between microbial communities were present. The shared genus can signal communication between the endodontic and periodontal microbiomes.

An In Vitro Model to Study the Colonization and Tubular Invasion of Enterococcus faecalis

INTRODUCTION

The purpose of this study was to examine the colonization and tubular invasion of Enterococcus faecalis in minimally altered canal walls. We hypothesized that age, axial directions (buccolingual or mesiodistal), regions (apical, midroot, or cervical), and disinfection treatment (sodium hypochlorite or autoclave) would impact bacterial colonization and invasion patterns.

METHODS

Single roots of extracted teeth from 2 age groups (≤30 years old and ≥60 years old) were challenged with bacteria for 2 weeks. Colonization on the canal walls in 3 regions was evaluated with scanning electron microscopy. The prevalence of tubular invasion in the axial directions in 3 regions was examined with confocal laser scanning microscopy. The data were analyzed using the GLIMMIX procedure in SAS software (SAS Institute Inc, Cary, NC) with a Tukey adjustment for comparisons.

RESULTS

Bacteria successfully colonized and invaded tubules in 2 weeks. The apical region in the ≥60-year age group was the least infected. A significantly higher invasion prevalence in a buccolingual (B/L) than a mesiodistal (M/D) direction was detected in both age groups and in all 3 regions. The ≤30-year age group had a significantly higher prevalence of tubular invasion than the ≥60-year age group in the B/L and M/D direction, respectively. Sodium hypochlorite treatment significantly impacted bacterial colonization and invasion in more calcified areas.

CONCLUSIONS

Our data support a more conservative enlargement of the apical region of older teeth. An emphasis in a B/L direction rather than an M/D direction is recommended for debridement.

Metaproteome and metabolome of oral microbial communities

The emergence of high-throughput technologies for the comprehensive measurement of biomolecules, also referred to as "omics" technologies, has helped us gather "big data" and characterize microbial communities. In this article, we focus on metaproteomic and metabolomic approaches that support hypothesis-driven investigations on various oral biologic samples. Proteomics reveals the working units of the oral milieu and metabolomics unveils the reactions taking place; and so these complementary techniques can unravel the functionality and underlying regulatory processes within various oral microbial communities. Current knowledge of the proteomic interplay and metabolic interactions of microorganisms within oral biofilm and salivary microbiome communities is presented and discussed, from both clinical and basic research perspectives. Communities indicative of, or from, health, caries, periodontal diseases, and endodontic lesions are represented. Challenges, future prospects, and examples of best practice are given.

Correlation between the clinically diagnosed inflammatory process and periapical index scores in severely painful endodontically involved teeth

Aim

To assess and correlate three distinct states of severely painful endodontically derived inflammation with their depiction on periapical radiographs using periapical index (PAI) scores.

Methodology

During a period of 15 months, 368 consecutively enrolled patients with suspected endodontic emergency conditions were examined at the University of Zurich, Center of Dental Medicine. Cases with a severely painful (numeric rating scale, NRS‐11 > 6) endodontically involved tooth and a clear pulpal and apical diagnosis (n = 162) were selected (one tooth per patient). Teeth were divided into three groups according to the clinically diagnosed main location of the inflammatory process: level 1: pulp (positive response to cold test), level 2: periodontium (no response to cold without swelling) and level 3: periapical tissues (no response to cold with swelling). Periapical radiographs were obtained using a digital unit and analysed by two calibrated observers. For level 2, which had the highest PAI variance (n = 76), the PAI scores were further scrutinized regarding their dependence on tooth location and the duration of pain. Data were analysed using chi‐squared and non‐parametric tests, alpha = 0.05.

Results

Overall, the PAI scores correlated well with the clinically diagnosed main location of periapical inflammation (Spearman’s rho = 0.5131, P < 0.001), with level 1 having the lowest scores by far (P < 0.001) and level 2 having significantly lower scores compared to level 3 (P < 0.05). However, a PAI score of 5 was found in merely 3 teeth within the entire cohort, and 49% of the teeth in the level 2 group had no radiolucency (PAI < 3). Within level 2, the PAI scores were not dependent on tooth location but were substantially (P < 0.001) higher for teeth which had hurt for more than one week, and for root filled teeth.

Conclusions

For the analysed, severely painful endodontically involved teeth, the clinically diagnosed main location of inflammation was reflected by the periapical index. PAI scores were not significantly influenced by anatomical noise, yet in some cases under‐estimated the clinical situation.

Qualitative and quantitative molecular analysis of bacteria in root canals of primary teeth with pulp necrosis

Information about bacterial diversity, such as the number of each species in the root canals of primary teeth, contributes to improving our effective management of infections of endodontic origin in primary teeth. This study made a qualitative and quantitative assessment of the bacteria in the root canals of primary teeth with necrotic pulp, using the fluorescence in situ hybridization (FISH) technique. Thirty-one primary teeth with pulp necrosis from 31 children were evaluated using the FISH technique, to detect the presence and density of Aggregatibacter actinomycetemcomitans, Campylobacter rectus, Enterococcus faecalis, Fusobacterium nucleatum, Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Streptococcus, Streptococcus mutans, Streptococcus sobrinus, Tannerella forsythia and Treponema denticola. Descriptive measures explained the data related to density, and Student's t-test assessed the differences among the densities of each bacterium, according to signs and symptoms. The bacterial density was paired and correlated. All bacteria tested were detected and identified in all the samples. The average number of bacterial individuals from each species ranged from 1.9 x 108 cells/mL (S. mutans) to 3.1 x 108 cells/mL (F. nucleatum) (p > 0.05). The sum of the mean counts of each bacterium represented almost 80% of the entire microbial community. Patients with pain had significantly more T. denticola, and those with edema showed a greater density of Streptococcus and P. nigrescens (p < 0.05). This study revealed that all 12 bacteria evaluated were found in all primary teeth with pulp necrosis. There was no predominance among the species studied; all species had a similar number of individuals.

Endodontic Microbiome of Fractured Non-vital Teeth in Dogs Determined by 16S rRNA Gene Sequencing

Dental fractures resulting in pulp exposure will lead to an endodontic infection with microbes from the oral cavity. However, data on the endodontic microbial composition in veterinary dentistry is lacking. The aim of this study was to examine the microbiome of naturally occurring primary endodontic infections in client-owned dogs. The endodontic microbiome of 10 non-vital teeth with exposed pulp cavities was assessed using a 16S rRNA gene sequencing approach. The results were compared to the microbiome of the subgingival plaque of the same teeth. Analysis revealed an abundant mixed microflora of a comparable richness and diversity and with mostly the same phyla obtained from sulcal and endodontic samples. However, further analysis revealed significant differences between sulcal and endodontic samples in the relative abundance of the most abundant phyla and genera, with the relative abundance of Bacteriodetes being significantly higher in endodontic samples. Although each sample presented a particular profile regarding the genera identified, Bacteroides was the most abundant genus in the endodontic samples. Snowella was also significantly more abundant in endodontic samples, while Porphyromonas and Fusobacterium were significantly more abundant in sulcal samples. We confirmed that the microbiome of the diseased endodontic system is comparably abundant with microorganisms to the healthy subgingival plaque indicating that previous culture-based studies of primary endodontic infections in dogs underestimated the richness and diversity of the endodontic microbiota.

IL-33 guides osteogenesis and increases proliferation and pluripotency marker expression in dental stem cells

Objectives

Soluble IL‐33 (interleukin (IL)‐1‐like cytokine) acts as endogenous alarm signal (alarmin). Since alarmins, besides activating immune system, act to restore tissue homeostasis, we investigated whether IL‐33 exerts beneficial effects on oral stem cell pull.

Materials and Methods

Clonogenicity, proliferation, differentiation and senescence of stem cells derived from human periodontal ligament (PDLSCs) and dental pulp (DPSCs) were determined after in vitro exposure to IL‐33. Cellular changes were detected by flow cytometry, Western blot, immunocytochemistry and semiquantitative RT‐PCR.

Results

IL‐33 stimulated proliferation, clonogenicity and expression of pluripotency markers, OCT‐4, SOX‐2 and NANOG, but it inhibited ALP activity and mineralization in both PDLSCs and DPSCs. Higher Ki67 expression and reduced β‐galactosidase activity in IL‐33‐treated cells were demonstrated, whereas these trends were more conspicuous in osteogenic medium. However, after 7‐day IL‐33 pretreatment, differentiation capacity of IL‐33‐pretreated cells was retained, and increased ALP activity was observed in both cell types. Results showed that IL‐33 regulates NF‐κB and β‐catenin signalling, indicating the association of these molecules with changes observed in IL‐33‐treated PDLSCs and DPSCs, particularly their proliferation, pluripotency‐associated marker expression and osteogenesis.

Conclusions

IL‐33 treatment impairs osteogenesis of PDLSCs and DPSCs, while increases their clonogenicity, proliferation and pluripotency marker expression. After exposure to IL‐33, osteogenic capacity of cells stayed intact. NF‐κB and β‐catenin are implicated in the effects achieved by IL‐33 in PDLSCs and DPSCs.

Endodontic Microbiology and Pathobiology: Current State of Knowledge

Newer research tools and basic science knowledge base have allowed the exploration of endodontic diseases in the pulp and periapical tissues in novel ways. The use of next generation sequencing, bioinformatics analyses, genome-wide association studies, to name just a few of these innovations, has allowed the identification of hundreds of microorganisms and of host response factors. This review addresses recent advances in endodontic microbiology and the host response and discusses the potential for future innovations in this area.

Antibacterial efficacy of an endodontic sonic-powered irrigation system: An in vitro study

OBJECTIVE

To evaluate the efficacy of EDDY, a new sonic-powered irrigation system, in reducing intracanal bacteria load.

METHODS

Thirty-eight instrumented, autoclaved single-rooted human premolars were inoculated with Enterococcus faecalis (ATCC-29212) for 21 days. Two teeth were used as negative control without bacterial contamination. For the bacteria-inoculated teeth, 6 were used as positive control without irrigation. The remaining 30 teeth were randomly divided into 2 groups (N = 15), using 3% NaOCl as irrigant: (A) 30-gauge syringe needle irrigation (SNI), (B) EDDY (VDW, Munich, Germany). Twelve teeth per group and 4 teeth in the positive control were evaluated for bacterial reduction using MTT assay. The remaining teeth were split for BacLight LIVE/DEAD staining to examine the percentages of live/dead bacteria present in the dentinal tubules from different canal locations (coronal, mid-root and apical portions of the canal space) using confocal laser scanning microscopy (CLSM).

RESULTS

MTT assay indicated that both SNI and EDDY significantly reduced overall intracanal bacterial load compared with the positive control, with no significant difference between the two techniques. CLSM indicated that EDDY had better intratubular bacterial killing efficacy than SNI in the coronal and mid-root portions of the canal space only but not in the apical portion. In all canal locations (coronal, mid-root apical), both systems failed to eliminate bacteria that proliferated deep within the dentinal tubules.

CONCLUSION

With the use of 3% NaOCl, sonic-powered irrigant activation with EDDY tips did not provide additional advantage over SNI in killing Enterococcus faecalis from deep intraradicular dentin.

CLINICAL SIGNIFICANCE

Both the sonic-powered root canal irrigant activation system and syringe needle irrigation can reduce intracanal bacteria load but are incapable of completely killing all bacteria that resided deep within the dentinal tubules of root canals infected with Enterococcus faecalis.

Apical periodontitis: preliminary assessment of microbiota by 16S rRNA high throughput amplicon target sequencing

Background

Apical periodontitis includes periapical granulomas and radicular cysts, which are histologically distinguished by the absence and the presence of an epithelial lining, respectively. The main cause of apical periodontitis is the bacterial colonization of the root canal space. This research aimed at assessing whether and how periapical granulomas and radicular cysts differ in terms of microbiota using high throughput amplicon target sequencing (HTS) techniques.

Methods

This study included 5 cases of Periapical Granulomas (PGs) and 5 cases of Radicular Cysts (RCs) selected on the base of histology out of 37 patients from January 2015 to February 2016. Complete medical history, panoramic radiograms (OPTs) and histologic records of each patient were assessed. Only lesions greater than 1 cm in diameter and developed in proximity to teeth with bad prognosis were included. The microbiota present in periapical granulomas and radicular cysts thus retrieved was finely characterized by pyrosequencing of the 16S rRNA genes.

Results

The core of OTUs shared between periapical granulomas and radicular cysts was dominated by the presence of facultative anaerobes taxa such as: Lactococcus lactis, Propionibacterium acnes, Staphylococcus warneri, Acinetobacter johnsonii and Gemellales. L. lactis, the main OTUs of the entire datasets, was associated with periapical granuloma samples. Consistently with literature, the anaerobic taxa detected were most abundant in radicular cyst samples. Indeed, a higher abundance of presumptive predicted metabolic pathways related to Lipopolysaccharide biosynthesis was found in radicular cyst samples.

Conclusions

The present pilot study confirmed the different microbial characterization of the two main apical periodontitis types and shade light on the possible role of L. lactis in periapical granulomas.

Application of Metagenomic Analyses in Dentistry as a Novel Strategy Enabling Complex Insight into Microbial Diversity of the Oral Cavity

The composition of the oral microbiome in healthy individuals is complex and dynamic, and depends on many factors, such as anatomical location in the oral cavity, diet, oral hygiene habits or host immune responses. It is estimated at present that worldwide about 2 billion people suffer from diseases of the oral cavity, mainly periodontal disease and dental caries. Importantly, the oral microflora involved in local infections may spread and cause systemic, even life-threatening infections. In search for etiological agents of infections in dentistry, traditional approaches are not sufficient, as about 50% of oral bacteria are not cultivable. Instead, metagenomic analyses are particularly useful for studies of the complex oral microbiome - both in healthy individuals, and in patients with oral and dental diseases. In this paper we review the current and future applications of metagenomic studies in evaluation of both the composition of the oral microbiome as well as its potential pathogenic role in infections in dentistry.

Root canal irrigants influence the hydrophobicity and adherence of Staphylococcus epidermidis to root canal dentin: an in vitro study

Objectives

To determine the effect of root canal irrigants on the hydrophobicity and adherence of Staphylococcus epidermidis (S. epidermidis) to root canal dentin in vitro.

Materials and Methods

Root dentin blocks (n = 60) were randomly divided into 4 groups based on the irrigation regimen: group 1, saline; group 2, 5.25% sodium hypochlorite (NaOCl); group 3, 5.25% NaOCl followed by 17% ethylenediaminetetraacetic acid (EDTA); group 4, same as group 3 followed by 2% chlorhexidine (CHX). The hydrophobicity of S. epidermidis to root dentin was calculated by cell surface hydrophobicity while the adherence was observed by fluorescence microscopy, and bacteria were quantified using ImageJ software (National Institutes of Health). Statistical analysis of the data was done using Kruskal-Wallis test and Mann-Whitney U test (p = 0.05).

Results

The hydrophobicity and adherence of S. epidermidis to dentin were significantly increased after irrigating with group 3 (NaOCl-EDTA) (p < 0.05), whereas in group 4 (NaOCl-EDTA-CHX) both hydrophobicity and adherence were significantly reduced (p < 0.05).

Conclusions

The adherence of S. epidermidis to dentin was influenced differently by root canal irrigants. Final irrigation with CHX reduces the bacterial adherence and may impact biofilm formation.

The Effect of Chlorhexidine Mixed with Mineral Trioxide Aggregate on Bacterial Leakage of Apical Plug in Simulated Immature Teeth Using Human Fresh Saliva

OBJECTIVES

Apexification is a challenging treatment in necrotic open apices teeth and bacterial leakage is the main reason for the treatment failure. The aim of this study is to compare the effect of mixing mineral trioxide aggregate (MTA) with chlorhexidine (CHX) on microbial leakage in apexification treatment of simulated immature teeth.

MATERIALS AND METHODS

In this experimental study, 44 intact central incisors were selected based on inclusion criteria. The coronal and 2 mm of apical part of the specimens were removed till all root segments were 12 mm long. The apical parts of the teeth were prepared using Profile #40/0.06 (Dentsply Maillefer, Ballaigues, Switzerland) in the apical to coronal direction to simulate open apices. The specimens were separated into experimental groups (n = 40) and control groups (n = 4). Group 1 delivered a 5 mm apical plug by MTA/H₂O and group 2 delivered an apical plug by MTA/CHX 0.12%. The positive control group had no apical barrier; on the other hand, the negative control group had an apical barrier and two layers of nail varnish on entire root surface. The microbial leakage assessment was done by a dual-chamber apparatus using fresh human saliva after 10-week follow-up. The turbidity of the lower chamber containing the Brain Heart Infusion (BHI) solution was analyzed based on the McFarland (0.5) standard which utilizes spectrophotometry results. Data analyses were done using Chi-square, Kaplan-Meier, and log-rank tests.

RESULTS

MTA/CHX group had lower microbial leakage percentage (P = 0.001) and longer time of leakage (P = 0.002) in compared with MTA/H₂O group and the difference was statistically meaningful.

CONCLUSION

Based on the results of this study, MTA/CHX mixture can reduce the amount of bacterial leakage.

Biofilms in Endodontics-Current Status and Future Directions

Microbiota are found in highly organized and complex entities, known as biofilms, the characteristics of which are fundamentally different from microbes in planktonic suspensions. Root canal infections are biofilm mediated. The complexity and variability of the root canal system, together with the multi-species nature of biofilms, make disinfection of this system extremely challenging. Microbial persistence appears to be the most important factor for failure of root canal treatment and this could further have an impact on pain and quality of life. Biofilm removal is accomplished by a chemo-mechanical process, using specific instruments and disinfecting chemicals in the form of irrigants and/or intracanal medicaments. Endodontic research has focused on the characterization of root canal biofilms and the clinical methods to disrupt the biofilms in addition to achieving microbial killing. In this narrative review, we discuss the role of microbial biofilms in endodontics and review the literature on the role of root canal disinfectants and disinfectant-activating methods on biofilm removal.

Modulation of infection-mediated migration of neutrophils and CXCR2 trafficking by osteopontin

Osteopontin (OPN) is a pro-inflammatory protein that paradoxically protects against inflammation and bone destruction in a mouse model of endodontic infection. Here we have tested the hypothesis that this effect of OPN is mediated by effects on migration of innate immune cells to the site of infection. Using the air pouch as a model of endodontic infection in mice, we showed that neutrophil accumulation at the site of infection with a mixture of endodontic pathogens is significantly reduced in OPN-deficient mice. Reduced neutrophil accumulation in the absence of OPN was accompanied by an increase in bacterial load. OPN-deficiency did not affect neutrophil survival, CXCR2 ligand expression, or the production of inflammatory cytokines in the air pouch. In vitro, OPN enhanced neutrophil migration to CXCL1, whereas in vivo, inhibition of CXCR2 suppressed cellular infiltration in air pouches of infected wild-type mice by > 50%, but had no effect in OPN-deficient mice. OPN increased cell surface expression of CXCR2 on bone marrow neutrophils in an integrin-α_v -dependent manner, and suppressed the internalization of CXCR2 in the absence of ligand. Together, these results support a model where the protective effect of OPN results from enhanced initial neutrophil accumulation at sites of infection resulting in optimal bacterial killing. We describe a novel mechanism for this effect of OPN: integrin-α_v -dependent suppression of CXCR2 internalization in neutrophils, which increases the ability of these cells to migrate to sites of infection in response to CXCR2 ligands.

In vitro and ex vivo microbial leakage assessment in endodontics: A literature review

The aim of this study was to perform a literature review of published in-vitro and ex-vivo studies, which evaluated microbial leakage in endodontics in the past 10 years. A comprehensive electronic literature search was carried out in PubMed database for English articles published from 2005 to 2016 using the keywords “endodontics,” “in vitro,” “ex vivo,” “microbial leakage,” “microbial penetration,” “saliva,” “Enterococcus faecalis,” “E. faecalis,” “endodontic sealers,” “temporary filling material,” “apical plug,” “mineral trioxide aggregate,” and “MTA.” The keywords were combined using Boolean operators AND/OR. Based on our search strategy, 33 relevant articles were included in the study. There are three main methods for assessment of bacterial microleakage, namely, (A) the dual-chamber leakage model, (B) detection of bacteria using a scanning electron microscope (SEM), and (C) polymerase chain reaction. All bacterial leakage models have some limitations and may yield different results compared to other microleakage evaluation techniques (i.e., dye penetration, fluid filtration, or electrochemical tests). The results of SEM correlated with those of microbial leakage test in most studies. Microbial leakage test using saliva better simulates the clinical setting for assessment of the leakage of single or mixed bacterial species.