Probiotic therapy for periodontal and peri-implant health - silver bullet or sham?

Probiotics are thought to be beneficial microbes that influence health-related outcomes through host immunomodulation and modulation of the bacteriome. Its reported success in the treatment of gastrointestinal disorders has led to further research on its potential applicability within the dental field due to similarities such as a polymicrobial aetiology and disease associated microbial-shifts. Although the literature is replete with studies demonstrating its efficacy, the use of probiotics in dentistry continues to polarise opinion. Here, we explore the evidence for probiotics and its effect on periodontal and peri-implant health. MEDLINE, EMBASE, and CENTRAL were systemically searched from June 2010 to June 2020 based on a formulated search strategy. Of 1,956 potentially relevant articles, we selected 27 double-blinded randomised clinical trials in the areas of gingivitis, periodontitis, residual pockets during supportive periodontal therapy, and peri-implant diseases, and reviewed their efficacy in these clinical situations. We observed substantial variation in treatment results and protocols between studies. Overall, the evidence for probiotic therapy for periodontal and peri-implant health appears unconvincing. The scarcity of trials with adequate power and follow-up precludes any meaningful clinical recommendations. Thus, the routine use of probiotics for these purposes are currently unsubstantiated. Further multi-centre trials encompassing a standardised investigation on the most promising strains and administration methods, with longer observation times are required to confirm the benefits of probiotic therapy for these applications.

Microbial Community-Driven Etiopathogenesis of Peri-Implantitis.

Osseointegrated dental implants are a revolutionary tool in the armament of reconstructive dentistry, employed to replace missing teeth and restore masticatory, occlusal, and esthetic functions. Like natural teeth, the orally exposed part of dental implants offers a pristine nonshedding surface for salivary pellicle-mediated microbial adhesion and biofilm formation. In early colonization stages, these bacterial communities closely resemble those of healthy periodontal sites, with lower diversity. Because the peri-implant tissues are more susceptible to endogenous oral infections, understanding of the ecological triggers that underpin the microbial pathogenesis of peri-implantitis is central to developing improved prevention, diagnosis, and therapeutic strategies. The advent of next-generation sequencing (NGS) technologies, notably applied to 16S ribosomal RNA gene amplicons, has enabled the comprehensive taxonomic characterization of peri-implant bacterial communities in health and disease, revealing a differentially abundant microbiota between these 2 states, or with periodontitis. With that, the peri-implant niche is highlighted as a distinct ecosystem that shapes its individual resident microbial community. Shifts from health to disease include an increase in diversity and a gradual depletion of commensals, along with an enrichment of classical and emerging periodontal pathogens. Metatranscriptomic profiling revealed similarities in the virulence characteristics of microbial communities from peri-implantitis and periodontitis, nonetheless with some distinctive pathways and interbacterial networks. Deeper functional assessment of the physiology and virulence of the well-characterized microbial communities of the peri-implant niche will elucidate further the etiopathogenic mechanisms and drivers of the disease.

Interventions to Reduce Aerosolized Microbes in Dental Practice: A Systematic Review with Network Meta-analysis of Randomized Controlled Trials.

The aim of this systematic review and network meta-analysis was to identify and rank the effectiveness of different interventions used in dental practice to reduce microbial load in aerosolized compounds. Seven electronic databases were searched to April 6, 2020, for randomized controlled trials (RCTs) or nonrandomized prospective studies in the field. Study selection, data extraction, and risk-of-bias assessment were performed for all included studies, while the outcome of interest pertained to differences in bacterial load quantification through the use of different interventions prior to aerosol-generating procedures in dental practices. Random effects frequentist network meta-analysis was performed, with mean difference (MD) and 95% CI as the effect measure. Confidence in the documented evidence was assessed through the newly fueled CINeMA framework (Confidence in Network Meta-analysis) based on the GRADE approach (Grading of Recommendations, Assessment, Development and Evaluation). Twenty-nine clinical trials were deemed eligible, 21 RCTs and 8 nonrandomized studies, while 11 RCTs contributed to the network meta-analysis, comprising 10 competing interventions. Tempered chlorhexidine (CHX) 0.2% as compared with nonactive control mouth rinse, prior to routine ultrasonic scaling, was most effective toward reduced postprocedural bacterial load with an MD of -0.92 (95% CI, -1.54 to -0.29) in log10 bacterial CFUs (colony-forming units). For CHX 0.2%, an MD of -0.74 (95% CI, -1.07 to -0.40) was observed as compared with control. Tempered CHX 0.2% presented the highest probabilities of being ranked the most effective treatment (31.2%). Level of confidence varied from very low to moderate across all formulated comparisons. These findings summarize the current state of research evidence in the field of aerosolized bacteria in dentistry. Instigated by the era of SARS-CoV-2 pandemic, the stipulation of a broader evaluation of the aerosolized microbes, including viruses, potentially coupled with disinfectant-based prevention schemes should be prioritized.

The influence of substrate surface conditioning and biofilm age on the composition of Enterococcus faecalis biofilms.

AIM: To investigate the null hypothesis that neither the surface conditioning (collagen, serum, saliva) of hydroxyapatite (HA) discs, nor the biofilm age (3 days vs. 21 days) has a significant effect on the cellular and matrix composition of biofilms, using Enterococcus faecalis as the model organism. METHODOLOGY: Sterile HA discs were conditioned with collagen, saliva or serum, and inoculated with E. faecalis to form 3-day and 21-day-old biofilms. Unconditioned discs served as controls. The biofilms were analysed using culture-dependent and independent (confocal microscopy and biochemical analysis) methods, to determine the colony-forming units and the biofilm matrix composition (polysaccharides and proteins), respectively. Statistical analyses were performed using appropriate parametric and nonparametric tests (P = 0.05). RESULTS: Collagen conditioning significantly increased the number of CFUs in the 21-day biofilms, compared to the 3-day biofilms (P < 0.05). Although the biochemical analysis revealed that surface conditioning had no significant effect on the total carbohydrate content in the 21-day biofilms, confocal microscopic analysis revealed that collagen and saliva conditioning selectively increased the polysaccharide content of 21-day biofilms, compared to the 3-day biofilms (P < 0.05). CONCLUSIONS: The results of this study raise an important methodological concern that the substrate conditioning substances and biofilm age differentially influence the cellular and extracellular matrix components of E. faecalis biofilms.

Regulation of PGLYRP1 and TREM-1 during Progression and Resolution of Gingival Inflammation.

INTRODUCTION: The triggering receptor expressed on myeloid cells 1 (TREM-1) signaling pathway is stimulated by bacteria and, together with its putative ligand peptidoglycan recognition protein 1 (PGLYRP1), propagates proinflammatory responses. OBJECTIVES: We aimed to evaluate the TREM-1/PGLYRP1/interleukin (IL)-1ß regulation in response to biofilm accumulation and removal in an experimental human gingivitis model. METHODS: The study (n = 42 participants, mean age: 23.8 ± 3.7 y) comprised a recruitment step (day -14) followed by experimentally induced biofilm formation (induction [I] phase, day 0 to +21) and a 2-wk resolution (R) phase (day +21 to +35). Plaque was recorded by the Modified Quigley and Hein Plaque Index (TQHPI), while records of gingival inflammation were based on the Modified Gingival Index (MGI). Unstimulated whole saliva supernatants (n = 210, 5 time points) were tested for TREM-1, PGLYRP1, and IL-1ß by enzyme-linked immunosorbent assay. RESULTS: During the I-phase, concentrations of all analytes showed a tendency for downregulation at day +7 compared to day 0. TREM-1 (P = 0.019) and PGLYRP1 (P = 0.007) increased significantly between day +7 and day +21. Although all analyte levels decreased during the R-phase, the difference was not significant except TREM-1 being at borderline significance (P = 0.058). Moreover, TREM-1, PGLYRP1, and IL-1ß showed significant positive correlations (P < 0.0001) with each other. The study participants were grouped into "fast" and "slow" responders based on clinical gingival inflammation scores. At each time point, fast responders showed significantly higher concentrations of TREM-1 (P < 0.025), PGLYRP1 (P < 0.007), and IL-1ß (P < 0.025) compared to slow responders. Mixed-effects multilevel regression analyses revealed that PGLYRP1 (P = 0.047) and IL-1ß (P = 0.005) showed a significant positive association with the MGI scores. CONCLUSION: The study demonstrated that TREM-1 and PGLYRP1 are regulated in response to biofilm accumulation and removal, and fast responders demonstrated higher levels of these analytes compared to slow responders. KNOWLEDGE TRANSFER STATEMENT: The results of this study demonstrated the suitability of salivary TREM-1 and PGLYRP1 to reflect biofilm accumulation and removal and PGLYRP1 to monitor the progression and resolution of inflammation in gingivitis-susceptible individuals (fast responders). Combined with conventional risk factors, the molecular toolbox proposed here should be further validated in future studies to confirm whether it can be used for population-based monitoring and prevention of gingivitis.

Streptococcus oralis maintains homeostasis in oral biofilms by antagonizing the cariogenic pathogen Streptococcus mutans.

Bacteria residing in oral biofilms live in a state of dynamic equilibrium with one another. The intricate synergistic or antagonistic interactions between them are crucial for determining this balance. Using the six-species Zürich "supragingival" biofilm model, this study aimed to investigate interactions regarding growth and localization of the constituent species. As control, an inoculum containing all six strains was used, whereas in each of the further five inocula one of the bacterial species was alternately absent, and in the last, both streptococci were absent. Biofilms were grown anaerobically on hydroxyapatite disks, and after 64 h they were harvested and quantified by culture analyses. For visualization, fluorescence in situ hybridization and confocal laser scanning microscopy were used. Compared with the control, no statistically significant difference of total colony-forming units was observed in the absence of any of the biofilm species, except for Fusobacterium nucleatum, whose absence caused a significant decrease in total bacterial numbers. Absence of Streptococcus oralis resulted in a significant decrease in Actinomyces oris, and increase in Streptococcus mutans (P < .001). Absence of A. oris, Veillonella dispar or S. mutans did not cause any changes. The structure of the biofilm with regards to the localization of the species did not result in observable changes. In summary, the most striking observation of the present study was that absence of S. oralis resulted in limited growth of commensal A. oris and overgrowth of S. mutans. These data establish highlight S. oralis as commensal keeper of homeostasis in the biofilm by antagonizing S. mutans, so preventing a caries-favoring dysbiotic state.

Immune response profiling of primary monocytes and oral keratinocytes to different Tannerella forsythia strains and their cell surface mutants.

The oral pathogen Tannerella forsythia possesses a unique surface (S-) layer with a complex O-glycan containing a bacterial sialic acid mimic in the form of either pseudaminic acid or legionaminic acid at its terminal position. We hypothesize that different T. forsythia strains employ these stereoisomeric sugar acids for interacting with the immune system and resident host tissues in the periodontium. Here, we show how T. forsythia strains ATCC 43037 and UB4 displaying pseudaminic acid and legionaminic acid, respectively, and selected cell surface mutants of these strains modulate the immune response in monocytes and human oral keratinocytes (HOK) using a multiplex immunoassay. When challenged with T. forsythia, monocytes secrete proinflammatory cytokines, chemokines and vascular endothelial growth factor (VEGF) with the release of interleukin-1ß (IL-1ß) and IL-7 being differentially regulated by the two T. forsythia wild-type strains. Truncation of the bacteria's O-glycan leads to significant reduction of IL-1ß and regulates macrophage inflammatory protein-1. HOK infected with T. forsythia produce IL-1Ra, chemokines and VEGF. Although the two wild-type strains elicit preferential immune responses for IL-8, both truncation of the O-glycan and deletion of the S-layer result in significantly increased release of IL-8, granulocyte-macrophage colony-stimulating factor and monocyte chemoattractant protein-1. Through immunofluorescence and confocal laser scanning microscopy of infected HOK we additionally show that T. forsythia is highly invasive and tends to localize to the perinuclear region. This indicates, that the T. forsythia S-layer and attached sugars, particularly pseudaminic acid in ATCC 43037, contribute to dampening the response of epithelial tissues to initial infection and hence play a pivotal role in orchestrating the bacterium's virulence.

Titanium ions form particles that activate and execute interleukin-1ß release from lipopolysaccharide-primed macrophages.

BACKGROUND AND OBJECTIVE: Peri-implantitis is a destructive inflammatory process characterized by destruction of the implant-supporting bone. Inflammasomes are large intracellular multiprotein complexes that play a central role in innate immunity by activating the release of proinflammatory cytokines. Although inflammasome activation has previously been linked to periodontal inflammation, there is still no information on a potential association with peri-implantitis. The aim of this study was to examine cytotoxic and proinflammatory effects, including inflammasome activation, of metals used in dental implants, in an in vitro model, as well as from clinical tissue samples. MATERIAL AND METHODS: Human macrophages were exposed to different metals [titanium (Ti), cobalt, chromium and molybdenum] in a cell-culture assay. Cytotoxicity was determined using the neutral red uptake assay. Cytokine secretion was quantified using an ELISA, and the expression of genes of various inflammasome components was analysed using quantitative PCR. In addition, the concentrations of interleukin-1ß (IL-1ß) and Ti in mucosal tissue samples taken in the vicinity of dental implants were determined using ELISA and inductively coupled plasma mass spectrometry, respectively. RESULTS: Ti ions in physiological solutions stimulated inflammasome activation in human macrophages and consequently IL-1ß release. This effect was further enhanced by macrophages that have been exposed to lipopolysaccharides. The proinflammatory activation caused by Ti ions disappeared after filtration (0.22 µm), which indicates an effect of particles. Ti ions alone did not stimulate transcription of the inflammasome components. The Ti levels of tissue samples obtained in the vicinity of Ti implants were sufficiently high (≥ 40 µm) to stimulate secretion of IL-1ß from human macrophages in vitro. CONCLUSION: Ti ions form particles that act as secondary stimuli for a proinflammatory reaction.

FISHing for gutta-percha-adhered biofilms in purulent post-treatment apical periodontitis.

This study investigated the possibility of depicting individual taxa in clinically relevant biofilms using fluorescent in situ hybridization (FISH). Gutta-percha samples were collected from the apical aspect of root canals associated with a chronic apical abscess (test samples, n = 8). Corresponding control samples were obtained from previously filled root canals with apparently normal periapical tissues (n = 3). The transport medium was investigated for detached biofilm fragments using FISH staining and conventional epifluorescence microscopy. Gutta-percha samples were stained by multiplex FISH, and inspected using confocal laser scanning microscopy. FISH of the transport medium confirmed the presence of the main species formerly identified by conventional methods in post-treatment purulent endodontic infections, most prominently Fusobacterium spp., Bacteroidetes and Prevotellaceae. Treponemes were identified in five of eight cases associated with purulent infections, but Enterococcus faecalis and Staphylococcus spp. were not identified. The biofilms on gutta-percha from root canals associated with apical periodontitis showed dense aggregates of variable composition. Control samples contained few, if any, bacteria in the transport medium, and featured no biofilms on the respective gutta-percha specimens. The current study revealed some direct, visual in situ information on the nature of biofilms associated with purulent periapical infections in man.

Microbial dynamics during conversion from supragingival to subgingival biofilms in an in vitro model.

The development of dental caries and periodontal diseases result from distinct shifts in the microbiota of the tooth-associated biofilm. This in vitro study aimed to investigate changes in biofilm composition and structure, during the shift from a 'supragingival' aerobic profile to a 'subgingival' anaerobic profile. Biofilms consisting of Actinomyces oris, Candida albicans, Fusobacterium nucleatum, Streptococcus oralis, Streptococcus mutans and Veillonella dispar were aerobically grown in saliva-containing medium on hydroxyapatite disks. After 64 h, Campylobacter rectus, Prevotella intermedia and Streptococcus anginosus were further added along with human serum, while culture conditions were shifted to microaerophilic. After 96 h, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola were finally added and the biofilm was grown anaerobically for another 64 h. At the end of each phase, biofilms were harvested for species-specific quantification and localization. Apart from C. albicans, all other species gradually increased during aerobic and microaerophilic conditions, but remained steady during anaerobic conditions. Biofilm thickness was doubled during the microaerophilic phase, but remained steady throughout the anaerobic phase. Extracellular polysaccharide presence was gradually reduced throughout the growth period. Biofilm viability was reduced during the microaerophilic conversion, but was recovered during the anaerobic phase. This in vitro study has characterized the dynamic structural shifts occurring in an oral biofilm model during the switch from aerobic to anaerobic conditions, potentially modeling the conversion of supragingival to subgingival biofilms. Within the limitations of this experimental model, the findings may provide novel insights into the ecology of oral biofilms.

Secretome of gingival epithelium in response to subgingival biofilms.

Periodontitis is the chronic inflammatory destruction of periodontal tissues as a result of bacterial biofilm formation on the tooth surface. Proteins secreted by the gingival epithelium challenged by subgingival biofilms represent an important initial response for periodontal inflammation. The aim of this in vitro study was to characterize the whole secreted proteome of gingival epithelial tissue challenged by subgingival biofilms, and to evaluate the differential effects of the presence of the red-complex species in the biofilm. Multi-layered human gingival epithelial cultures were challenged with a 10-species in vitro biofilm model or its seven-species variant excluding the red complex. Liquid chromatography-tandem mass spectrometry for label-free quantitative proteomics was applied to identify and quantify the secreted epithelial proteins in the culture supernatant. A total of 192 proteins were identified and quantified. The biofilm challenge resulted in more secreted proteins being downregulated than upregulated. Even so, presence of the red complex in the biofilm was responsible for much of this downregulatory effect. Over 24 h, the upregulated biological processes were associated with inflammation and apoptosis, whereas the downregulated processes were associated with the disruption of epithelial tissue integrity and impairment of tissue turnover. Over 48 h, negative regulation of several metabolic processes and degradation of various molecular complexes was further intensified. Again, many of these biological regulations were attributed to the presence of the red complex. In conclusion, the present study provides the secreted proteome profile of gingival epithelial tissue to subgingival biofilms, and identifies a significant role for the red-complex species in the observed effects.

Expression and regulation of triggering receptor expressed on myeloid cells 1 in periodontal diseases.

Periodontitis is an inflammatory infectious disease that destroys the tooth-supporting tissues. It is caused by multi-species subgingival biofilms that colonize the tooth surface. Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia (i.e. 'red complex' bacteria) are characteristic subgingival biofilm species. The triggering receptor expressed on myeloid cells 1 (TREM-1) is a cell surface receptor of the immunoglobulin superfamily, with a role in the amplification of proinflammatory cytokine production during infection. This study aimed to investigate TREM-1 mRNA expression in gingival tissues from patients with chronic periodontitis, generalized aggressive periodontitis and healthy subjects and its correlation with the levels of periodontal pathogens in the tissue. A further aim was to investigate the regulation of TREM-1 in human monocytic cells (MM6) challenged with an in-vitro subgingival biofilm model. Gingival tissue TREM-1 expression was increased in both chronic and aggressive periodontitis, compared to health, and correlated with the levels of the 'red complex' species in the tissue. No significant differences were detected between the two forms of periodontitis. Biofilm-challenged MM6 cells exhibited higher TREM-1 expression and secretion compared to controls, with partial involvement of the 'red complex'. Engagement or inhibition of TREM-1 affected the capacity of the biofilms to stimulate interleukin (IL)-1ß, but not IL-8, secretion by the cells. In conclusion, this study reveals that TREM-1 tissue expression is enhanced in periodontal disease, and correlates with the level of periodontal pathogens. It also provides a mechanistic insight into the regulation of TREM-1 expression and the associated IL-1ß production in biofilm-challenged monocytes.

Transcriptional profiling of human gingival fibroblasts in response to multi-species in vitro subgingival biofilms.

Periodontitis is an infectious inflammatory disease that destroys the tooth-supporting tissues. It is initiated by complex subgingival biofilms, triggering an inflammatory response by the juxtaposed gingival tissue. The range of transcriptional events initiated in the gingiva following biofilm challenge is not fully elucidated. By employing gene microarray technology, this study aimed to characterize the overall transcriptional changes (more than two-fold regulation) of cultured human gingival fibroblasts in response to a 10-species in vitro subgingival biofilm model (BF), over a challenge period of 6 h. The relative involvement of the three 'red complex' species in these transcriptional events was evaluated by omitting these species from the biofilm composition (BF-RC). When compared with the unchallenged control, challenge with BF and BF-RC differentially regulated 386 and 428 genes, respectively, with an overlap of 52-75%. Interestingly, the expression of only three genes was significantly different between the BF and BF-RC challenged groups. There was also a strong overlap of the affected signalling pathways and gene ontology processes. These signalling pathways involved primarily the immune response, and included toll-like receptors, interleukin-1, interleukin-17 and heat-shock proteins 60 and 70. In conclusion, subgingival biofilms elicited a large number of transcriptional changes in gingival fibroblasts, while the presence of the 'red complex' in the biofilm did not yield any substantial differences. These findings show a uniform 'non-specific' transcriptional response of host cells to subgingival biofilms, and denote that redundancies may exist in the virulence properties of individual bacterial species within a polymicrobial biofilm community.

Synergistetes cluster A in saliva is associated with periodontitis.

BACKGROUND AND OBJECTIVES: Synergistetes is a novel bacterial phylum consisting of gram-negative anaerobes. Increasing lines of evidence demonstrate that this phylum is associated with periodontal diseases. This study aimed to compare the presence and levels of Synergistetes clusters A and B, in saliva of patients with chronic periodontitis (CP), generalized aggressive periodontitis (G-AgP) and non-periodontitis subjects, and investigate their correlation with clinical parameters. MATERIAL AND METHODS: Saliva was collected from patients with CP (n = 20), G-AgP (n = 21) and non-periodontitis subjects (n = 18). Full mouth clinical periodontal measurements were recorded. The numbers of Synergistetes cluster A and cluster B or the associated species Jonquetella anthropi were quantified by fluorescent in situ hybridization and microscopy. RESULTS: Synergistetes cluster A bacteria were detected more frequently, and at higher numbers and proportions in the two periodontitis groups, than the non-periodontitis control group. The prevalence was 27.7% in the control group, 85% in CP and 86% in G-AgP. Compared to the control group, the numbers were significantly higher by 12.5-fold in CP and 26.5-fold in G-AgP, whereas the difference between the two forms of periodontitis was not statistically significant. Within the total bacterial population, the proportion of this cluster was increased in CP and G-AgP compared to the control group, with the difference between the two forms of periodontitis being also significant. There was a positive correlation between the levels of Synergistetes cluster A in saliva and all full mouth clinical periodontal parameters. Nevertheless, Synergistetes cluster B bacteria and J. anthropi species were detected infrequently and at low levels in all the three subject groups. CONCLUSION: Synergistetes cluster A, but not cluster B, bacteria are found at higher prevalence, numbers and proportions in saliva from patients with periodontitis, than non-periodontitis subjects. These findings support the association of this cluster with periodontitis.

Validation of a quantitative real-time PCR assay and comparison with fluorescence microscopy and selective agar plate counting for species-specific quantification of an in vitro subgingival biofilm model.

BACKGROUND AND OBJECTIVE: Subgingival biofilms are the prime etiological factor of periodontal disease. Owing to their complex polymicrobial nature, quantification of individual bacterial species within the biofilm for research and diagnostic purposes can be methodologically challenging. The aims of this study were to establish a quantitative real-time PCR (qPCR) assay to quantify the bacteria used in our 10-species in vitro 'subgingival' biofilm model and to compare the quantitative outcome with fluorescence microscopy and colony-forming unit (CFU) counts on selective agar plates. MATERIAL AND METHODS: The 10 species included in the in vitro biofilm were Streptococcus oralis, Streptococcus anginosus, Veillonella dispar, Fusobacterium nucleatum, Treponema denticola, Tannerella forsythia, Actinomyces oris, Campylobacter rectus, Porphyromonas gingivalis and Prevotella intermedia. The numbers of each species were quantified at two time points using qPCR, microscopy counting following fluorescence in-situ hybridization (FISH) or immunofluorescence staining, and counting of CFUs after growth on selective agar plates. RESULTS: All 10 species were successfully quantified using qPCR and FISH or immunofluorescence, and the eight species culturable on selective agar plates were also quantified by counting the numbers of CFUs after growth on selective agar. In early biofilm cultures, all methods showed a significant correlation, although the absolute numbers differed between methods. In late biofilm cultures, measurements obtained using qPCR and FISH or immunofluorescence, but not by CFU counts, maintained significant correlation. CFU counts yielded lower values than did measurements made using the other two methods. CONCLUSION: Quantitative PCR and epifluorescence microscopy can be easily combined with each other to determine species-specific bacterial numbers within biofilms. However, conventional bacterial cultures cannot be as efficiently combined using these molecular detection methods. This may be crucial in designing and selecting appropriate clinical diagnostic methods for subgingival biofilm samples.

The receptor activator of NF-κB ligand-osteoprotegerin system in pulpal and periapical disease.

AIM: To summarize the collective in vitro, in vivo and clinical evidence of the involvement of the receptor activator of NF-κB ligand (RANKL)-osteoprotegerin (OPG) system, a system of two molecules controlling osteoclast differentiation and hard-tissue resorption, in pulpal and periapical pathophysiology. METHODOLOGY: A systematic search related to RANKL and/or OPG and pulp or periapical disease was conducted on Medline, Biosis, Cochrane, Embase and Web of Science databases using keywords and controlled vocabulary. No language restriction was applied. Two independent reviewers first screened titles and abstracts and then the full texts that were initially included. The reference lists of the identified publications were examined for additional titles. RESULTS: A total of 33 papers were identified. In vitro studies (N = 11) revealed that pulpal cells can be stimulated by various inflammatory agents to produce RANKL, whilst many studies did not consider the RANKL/OPG ratio. Animal studies (N = 9) mostly focused on the time course and development of periapical lesions in relation to the RANKL-OPG system. Levels of RANKL and OPG in the necrotizing pulp were not investigated. Human studies (N = 13) showed a steady-state expression of OPG in the odontoblast layer. Conflicting results have been reported regarding the role of RANKL in active apical periodontitis, again because the correlation of this molecule with its inhibitor (OPG) was often disregarded. CONCLUSIONS: There is relatively little information currently available that would highlight the specific role of RANKL and OPG in pulpal and periapical disease. OPG may play a protective role against internal resorption, whilst an increased periapical RANKL/OPG ratio might indicate bone resorption.

Elevated oral and systemic levels of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) in periodontitis.

The Triggering Receptor Expressed on Myeloid cells 1 (TREM-1) is a cell-surface receptor of the immunoglobulin superfamily, involved in the propagation of the inflammatory response to bacterial challenge. Soluble (s)TREM-1 is released from the cell surface during the course of infection and is a useful inflammatory biomarker in the early diagnosis of systemic sepsis. The hypothesis of this study was that oral and systemic levels of sTREM-1 are elevated in periodontitis. Therefore, the aim was to investigate, by ELISA, the sTREM-1 concentrations in saliva and serum of individuals without periodontitis (control) and persons with chronic or generalized aggressive periodontitis. In saliva, sTREM-1 concentrations were higher in chronic and aggressive periodontitis than in the control group, by 3.3-fold and 5.6-fold, respectively. In serum, these differences were 1.7-fold and 2-fold, respectively. However, there were no significant differences between the two forms of periodontitis, neither in saliva nor in serum. Salivary and serum sTREM-1 levels positively correlated with full-mouth clinical periodontal parameters. In conclusion, the increased oral and systemic levels of sTREM-1 in periodontitis denote a value for this molecule as a biomarker for the disease and may also have implications in the association between periodontal infections and systemic inflammatory response.

Healthcare-associated viral and bacterial infections in dentistry.

Infection prevention in dentistry is an important topic that has gained more interest in recent years and guidelines for the prevention of cross-transmission are common practice in many countries. However, little is known about the real risks of cross-transmission, specifically in the dental healthcare setting. This paper evaluated the literature to determine the risk of cross-transmission and infection of viruses and bacteria that are of particular relevance in the dental practice environment. Facts from the literature on HSV, VZV, HIV, Hepatitis B, C and D viruses, Mycobacterium spp., Pseudomonas spp., Legionella spp. and multi-resistant bacteria are presented. There is evidence that Hepatitis B virus is a real threat for cross-infection in dentistry. Data for the transmission of, and infection with, other viruses or bacteria in dental practice are scarce. However, a number of cases are probably not acknowledged by patients, healthcare workers and authorities. Furthermore, cross-transmission in dentistry is under-reported in the literature. For the above reasons, the real risks of cross-transmission are likely to be higher. There is therefore a need for prospective longitudinal research in this area, to determine the real risks of cross-infection in dentistry. This will assist the adoption of effective hygiene procedures in dental practice.

Expression and regulation of the NALP3 inflammasome complex in periodontal diseases.

Periodontitis is an infectious process characterized by inflammation affecting the supporting structures of the teeth. Porphyromonas gingivalis is a major oral bacterial species implicated in the pathogenesis of periodontitis. Processing of interleukin (IL)-1 family cytokines is regulated by an intracellular innate immune response system, known as the NALP3 [nacht domain-, leucine-rich repeat-, and pyrin domain (PYD)-containing protein 3] inflammasome complex. The aim of the present study was to investigate by quantitative real-time polymerase chain reaction (PCR) the mRNA expression of NALP3, its effector molecule apoptosis associated speck-like protein (ASC), its putative antagonist NLRP2 (NLR family, PYD-containing protein 2), IL-1beta and IL-18 (i) in gingival tissues from patients with gingivitis (n = 10), chronic periodontitis (n = 18), generalized aggressive periodontitis (n = 20), as well as in healthy subjects (n = 20), (ii) in vitro in a human monocytic cell line (Mono-Mac-6), in response to P. gingivalis challenge for 6 h. The clinical data indicate that NALP3 and NLRP2, but not ASC, are expressed at significantly higher levels in the three forms of inflammatory periodontal disease compared to health. Furthermore, a positive correlation was revealed between NALP3 and IL-1beta or IL-18 expression levels in these tissues. The in vitro data demonstrate that P. gingivalis deregulates the NALP3 inflammasome complex in Mono-Mac-6 cells by enhancing NALP3 and down-regulating NLRP2 and ASC expression. In conclusion, this study reveals a role for the NALP3 inflammasome complex in inflammatory periodontal disease, and provides a mechanistic insight to the host immune responses involved in the pathogenesis of the disease by demonstrating the modulation of this cytokine-signalling pathway by bacterial challenge.