In silico analysis of the competition between Streptococcus sanguinis and Streptococcus mutans in the dental biofilm

Competitive dynamics and balance between Streptococcus mutans and commensal streptococci in oral microecology

Dental caries, as a biofilm-related disease, is closely linked to dysbiosis in microbial ecology within dental biofilms. Beyond its impact on oral health, bacteria within the oral cavity pose systemic health risks by potentially entering the bloodstream, thereby increasing susceptibility to bacterial endocarditis, among other related diseases. Streptococcus mutans, a principal cariogenic bacterium, possesses virulence factors crucial to the pathogenesis of dental caries. Its ability to adhere to tooth surfaces, produce glucans for biofilm formation, and metabolize sugars into lactic acid contributes to enamel demineralization and the initiation of carious lesions. Its aciduricity and ability to produce bacteriocins enable a competitive advantage, allowing it to thrive in acidic environments and dominate in changing oral microenvironments. In contrast, commensal streptococci, such as Streptococcus sanguinis, Streptococcus gordonii, and Streptococcus salivarius, act as primary colonizers and compete with S. mutans for adherence sites and nutrients during biofilm formation. This competition involves the production of alkali, peroxides, and antibacterial substances, thereby inhibiting S. mutans growth and maintaining microbial balance. This dynamic interaction influences the balance of oral microbiota, with disruptions leading to shifts in microbial composition that are marked by rapid increases in S. mutans abundance, contributing to the onset of dental caries. Thus, understanding the dynamic interactions between commensal and pathogenic bacteria in oral microecology is important for developing effective strategies to promote oral health and prevent dental caries. This review highlights the roles and competitive interactions of commensal bacteria and S. mutans in oral microecology, emphasizing the importance of maintaining oral microbial balance for health, and discusses the pathological implications of perturbations in this balance.

Oral microbiota, co-evolution, and implications for health and disease: The case of indigenous peoples

Evidence indicates that oral microbiota plays a crucial role in human health and disease. For instance, diseases with multifactorial etiology, such as periodontitis and caries, which cause a detrimental impact on human well-being and health, can be caused by alterations in the host-microbiota interactions, where non-pathogenic bacteria give way to pathogenic orange/red-complex bacterial species (a change from a eubiotic to dysbiotic state). In this scenario, where thousands of oral microorganisms, including fungi, archaea, and phage species, and their host are co-evolving, a set of phenomena, such as the arms race and Red or Black Queen dynamics, are expected to operate. We review concepts on the subject and revisit the nature of bacterial complexes linked to oral health and diseases, as well as the problem of the bacterial resistome in the face of the use of antibiotics and what is the impact of this on the evolutionary trajectory of the members of this symbiotic ecosystem. We constructed a 16SrRNA tree to show that adaptive consortia of oral bacterial complexes do not necessarily rescue phylogenetic relationships. Finally, we remember that oral health is not exempt from health disparity trends in some populations, such as Native Americans, when compared with non-Indigenous people.

In Situ Raman Analysis of Biofilm Exopolysaccharides Formed in Streptococcus mutans and Streptococcus sanguinis Commensal Cultures

This study probed in vitro the mechanisms of competition/coexistence between Streptococcus sanguinis (known for being correlated with health in the oral cavity) and Streptococcus mutans (responsible for aciduric oral environment and formation of caries) by means of quantitative Raman spectroscopy and imaging. In situ Raman assessments of live bacterial culture/coculture focusing on biofilm exopolysaccharides supported the hypothesis that both species engaged in antagonistic interactions. Experiments of simultaneous colonization always resulted in coexistence, but they also revealed fundamental alterations of the biofilm with respect to their water-insoluble glucan structure. Raman spectra (collected at fixed time but different bacterial ratios) showed clear changes in chemical bonds in glucans, which pointed to an action by Streptococcus sanguinis to discontinue the impermeability of the biofilm constructed by Streptococcus mutans. The concurrent effects of glycosidic bond cleavage in water-insoluble α - 1,3-glucan and oxidation at various sites in glucans' molecular chains supported the hypothesis that secretion of oxygen radicals was the main "chemical weapon" used by Streptococcus sanguinis in coculture.

Glucose Phosphotransferase System Modulates Pyruvate Metabolism, Bacterial Fitness, and Microbial Ecology in Oral Streptococci

Spontaneous mutants with defects in the primary glucose phosphotransferase permease (manLMNO) of Streptococcus sanguinis SK36 showed enhanced fitness at low pH. Transcriptomics and metabolomics with a manL deletion mutant (SK36/manL) revealed redirection of pyruvate to production of acetate and formate, rather than lactate. These observations were consistent with measurements of decreased lactic acid accumulation and increased excretion of acetate, formate, pyruvate, and H2O2. Genes showing increased expression in SK36/manL included those encoding carbohydrate transporters, extracellular glycosidases, intracellular polysaccharide metabolism, and arginine deiminase and pathways for metabolism of acetoin, ethanolamine, ascorbate, and formate, along with genes required for membrane biosynthesis and adhesion. Streptococcus mutans UA159 persisted much better in biofilm cocultures with SK36/manL than with SK36, an effect that was further enhanced by culturing the biofilms anaerobically but dampened by adding arginine to the medium. We posited that the enhanced persistence of S. mutans with SK36/manL was in part due to excess excretion of pyruvate by the latter, as addition of pyruvate to S. mutans-S. sanguinis cocultures increased the proportions of UA159 in the biofilms. Reducing the buffer capacity or increasing the concentration of glucose benefited UA159 when cocultured with SK36, but not with SK36/manL, likely due to the altered metabolism and enhanced acid tolerance of the mutant. When manL was deleted in S. mutans or Streptococcus gordonii, the mutants presented altered fitness characteristics. Our study demonstrated that phosphotransferase system (PTS)-dependent modulation of central metabolism can profoundly affect streptococcal fitness and metabolic interactions, revealing another dimension in commensal-pathogen relationships influencing dental caries development. IMPORTANCE Dental caries is underpinned by a dysbiotic microbiome and increased acid production. As beneficial bacteria that can antagonize oral pathobionts, oral streptococci such as S. sanguinis and S. gordonii can ferment many carbohydrates, despite their relative sensitivity to low pH. We characterized the molecular basis for why mutants of glucose transporter ManLMNO of S. sanguinis showed enhanced production of hydrogen peroxide and ammonia and improved persistence under acidic conditions. A metabolic shift involving more than 300 genes required for carbohydrate transport, energy production, and envelope biogenesis was observed. Significantly, manL mutants engineered in three different oral streptococci displayed altered capacities for acid production and interspecies antagonism, highlighting the potential for targeting the glucose-PTS to modulate the pathogenicity of oral biofilms.

Optimization and Evaluation of the 30S-S11 rRNA Gene for Taxonomic Profiling of Oral Streptococci

Dental caries is a multifactorial disease driven by interactions between the highly complex microbial biofilm community and host factors like diet, oral hygiene habits, and age. The oral streptococci are one of the most dominant members of the plaque biofilm and are implicated in disease but also in maintaining oral health. Current methods used for studying the supragingival plaque community commonly sequence portions of the16S rRNA gene, which often cannot taxonomically resolve members of the streptococcal community past the genus level due to their sequence similarity. The goal of this study was to design and evaluate a more reliable and cost-effective method to identify oral streptococci at the species level by applying a new locus, the 30S-S11 rRNA gene, for high-throughput amplicon sequencing. The study results demonstrate that the newly developed single-copy 30S-S11 gene locus resolved multiple amplicon sequence variants (ASVs) within numerous species, providing much improved taxonomic resolution over 16S rRNA V4. Moreover, the results reveal that different ASVs within a species were found to change in abundance at different stages of caries progression. These findings suggest that strains of a single species may perform distinct roles along a biochemical spectrum associated with health and disease. The improved identification of oral streptococcal species will provide a better understanding of the different ecological roles of oral streptococci and inform the design of novel oral probiotic formulations for prevention and treatment of dental caries. IMPORTANCE The microbiota associated with the initiation and progression of dental caries has yet to be fully characterized. Although much insight has been gained from 16S rRNA hypervariable region DNA sequencing, this approach has several limitations, including poor taxonomic resolution at the species level. This is particularly relevant for oral streptococci, which are abundant members of oral biofilm communities and major players in health and caries disease. Here, we develop a new method for taxonomic profiling of oral streptococci based on the 30S-S11 rRNA gene, which provides much improved resolution over 16S rRNA V4 (resolving 10 as opposed to 2 species). Importantly, 30S-S11 can resolve multiple amplicon sequence variants (ASVs) within species, providing an unprecedented insight into the ecological progression of caries. For example, our findings reveal multiple incidences of different ASVs within a species with contrasting associations with health or disease, a finding that has high relevance toward the informed design of prebiotic and probiotic therapy.

Phytochemical Profile of Antibacterial Agents from Red Betel Leaf (Piper crocatum Ruiz and Pav) against Bacteria in Dental Caries

Based on data from The Global Burden of Disease Study in 2016, dental and oral health problems, especially dental caries, are a disease experienced by almost half of the world’s population (3.58 billion people). One of the main causes of dental caries is the pathogenesis of Streptococcus mutans. Prevention can be achieved by controlling S. mutans using an antibacterial agent. The most commonly used antibacterial for the treatment of dental caries is chlorhexidine. However, long-term use of chlorhexidine has been reported to cause resistance and some side effects. Therefore, the discovery of a natural antibacterial agent is an urgent need. A natural antibacterial agent that can be used are herbal medicines derived from medicinal plants. Piper crocatum Ruiz and Pav has the potential to be used as a natural antibacterial agent for treating dental and oral health problems. Several studies reported that the leaves of P. crocatum Ruiz and Pav contain secondary metabolites such as essential oils, flavonoids, alkaloids, terpenoids, tannins, and phenolic compounds that are active against S. mutans. This review summarizes some information about P. crocatum Ruiz and Pav, various isolation methods, bioactivity, S. mutans bacteria that cause dental caries, biofilm formation mechanism, antibacterial properties, and the antibacterial mechanism of secondary metabolites in P. crocatum Ruiz and Pav.

E-Cigarette Aerosol Exposure Favors the Growth and Colonization of Oral Streptococcus mutans Compared to Commensal Streptococci

E-cigarettes (e-cigs) have drastically increased in popularity during the last decade, especially among teenagers. While recent studies have started to explore the effect of e-cigs in the oral cavity, little is known about their effects on the oral microbiota and how they could affect oral health and potentially lead to disease, including periodontitis and head and neck cancers. To explore the impact of e-cigs on oral bacteria, we selected members of the genus Streptococcus, which are abundant in the oral cavity. We exposed the commensals Streptococcus sanguinis and Streptococcus gordonii and the opportunistic pathogen Streptococcus mutans, best known for causing dental caries, to e-liquids and e-cig aerosols with and without nicotine and with and without menthol flavoring and measured changes in growth patterns and biofilm formation. Our results demonstrate that e-cig aerosols hindered the growth of S. sanguinis and S. gordonii, while they did not affect the growth of S. mutans. We also show that e-cig aerosols significantly increased biofilm formation by S. mutans but did not affect the biofilm formation of the two commensals. We found that S. mutans exhibits higher hydrophobicity and coaggregation abilities along with higher attachment to OKF6 cells than S. sanguinis and S. gordonii. Therefore, our data suggest that e-cig aerosols have the potential to dysregulate oral bacterial homeostasis by suppressing the growth of commensals while enhancing the biofilm formation of the opportunistic pathogen S. mutans. This study highlights the importance of understanding the consequences of e-cig aerosol exposure on selected commensals and pathogenic species. Future studies modeling more complex communities will provide more insight into how e-cig aerosols and vaping affect the oral microbiota. IMPORTANCE Our study shows that e-cigarette aerosol exposure of selected bacteria known to be residents of the oral cavity hinders the growth of two streptococcal commensals while enhancing biofilm formation, hydrophobicity, and attachment for the pathogen S. mutans. These results indicate that e-cigarette vaping could open a niche for opportunistic bacteria such as S. mutans to colonize the oral cavity and affect oral health.

Influence of Fluoride-Resistant Streptococcus mutans Within Antagonistic Dual-Species Biofilms Under Fluoride In Vitro

The widespread application of fluoride, an extremely effective caries prevention agent, induces the generation of fluoride-resistant strains of opportunistic cariogenic bacteria such as fluoride-resistant Streptococcus mutans (S. mutans). However, the influence of this fluoride-resistant strain on oral microecological homeostasis under fluoride remains unknown. In this study, an antagonistic dual-species biofilm model composed of S. mutans and Streptococcus sanguinis (S. sanguinis) was used to investigate the influence of fluoride-resistant S. mutans on dual-species biofilm formation and pre-formed biofilms under fluoride to further elucidate whether fluoride-resistant strains would influence the anti-caries effect of fluoride from the point of biofilm control. The ratio of bacteria within dual-species biofilms was investigated using quantitative real-time PCR and fluorescence in situ hybridization. Cristal violet staining, scanning electron microscopy imaging, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay were used to evaluate biofilm biomass, biofilm structure, and metabolic activity, respectively. Biofilm acidogenicity was determined using lactic acid and pH measurements. The anthrone method and exopolysaccharide (EPS) staining were used to study the EPS production of biofilms. We found that, in biofilm formation, fluoride-resistant S. mutans occupied an overwhelming advantage in dual-species biofilms under fluoride, thus showing more biofilm biomass, more robust biofilm structure, and stronger metabolic activity (except for 0.275 g/L sodium fluoride [NaF]), EPS production, and acidogenicity within dual-species biofilms. However, in pre-formed biofilms, the advantage of fluoride-resistant S. mutans could not be fully highlighted for biofilm formation. Therefore, fluoride-resistant S. mutans could influence the anti-caries effect of fluoride on antagonistic dual-species biofilm formation while being heavily discounted in pre-formed biofilms from the perspective of biofilm control.

Spontaneous Mutants of Streptococcus sanguinis with Defects in the Glucose-Phosphotransferase System Show Enhanced Post-Exponential-Phase Fitness

Genetic truncations in a gene encoding a putative glucose-phosphotransferase system (PTS) protein (manL, EIIAB^Man) were identified in subpopulations of two separate laboratory stocks of Streptococcus sanguinis SK36; the mutants had reduced PTS activities on glucose and other monosaccharides. To understand the emergence of these mutants, we engineered deletion mutants of manL and showed that the ManL-deficient strain had improved bacterial viability in the stationary phase and was better able to inhibit the growth of the dental caries pathogen Streptococcus mutans. Transcriptional analysis and biochemical assays suggested that the manL mutant underwent reprograming of central carbon metabolism that directed pyruvate away from production of lactate, increasing production of hydrogen peroxide (H₂O₂) and excretion of pyruvate. Addition of pyruvate to the medium enhanced the survival of SK36 in overnight cultures. Meanwhile, elevated pyruvate levels were detected in the cultures of a small but significant percentage (∼10%) of clinical isolates of oral commensal bacteria. Furthermore, the manL mutant showed higher expression of the arginine deiminase system than the wild type, which enhanced the ability of the mutant to raise environmental pH when arginine was present. To our surprise, significant discrepancies in genome sequence were identified between strain SK36 obtained from ATCC and the sequence deposited in GenBank. As the conditions that are likely associated with the emergence of spontaneous manL mutations, i.e., excess carbohydrates and low pH, are those associated with caries development, we propose that glucose-PTS strongly influences commensal-pathogen interactions by altering the production of ammonia, pyruvate, and H₂O₂. IMPORTANCE A health-associated dental microbiome provides a potent defense against pathogens and diseases. Streptococcus sanguinis is an abundant member of a health-associated oral flora that antagonizes pathogens by producing hydrogen peroxide. There is a need for a better understanding of the mechanisms that allow bacteria to survive carbohydrate-rich and acidic environments associated with the development of dental caries. We report the isolation and characterization of spontaneous mutants of S. sanguinis with impairment in glucose transport. The resultant reprograming of the central metabolism in these mutants reduced the production of lactic acid and increased pyruvate accumulation; the latter enables these bacteria to better cope with hydrogen peroxide and low pH. The implications of these discoveries in the development of dental caries are discussed.

The oralome and its dysbiosis: New insights into oral microbiome-host interactions

The oralome is the summary of the dynamic interactions orchestrated between the ecological community of oral microorganisms (comprised of up to approximately 1000 species of bacteria, fungi, viruses, archaea and protozoa - the oral microbiome) that live in the oral cavity and the host. These microorganisms form a complex ecosystem that thrive in the dynamic oral environment in a symbiotic relationship with the human host. However, the microbial composition is significantly affected by interspecies and host-microbial interactions, which in turn, can impact the health and disease status of the host. In this review, we discuss the composition of the oralome and inter-species and host-microbial interactions that take place in the oral cavity and examine how these interactions change from healthy (eubiotic) to disease (dysbiotic) states. We further discuss the dysbiotic signatures associated with periodontitis and caries and their sequalae, (e.g., tooth/bone loss and pulpitis), and the systemic diseases associated with these oral diseases, such as infective endocarditis, atherosclerosis, diabetes, Alzheimer's disease and head and neck/oral cancer. We then discuss current computational techniques to assess dysbiotic oral microbiome changes. Lastly, we discuss current and novel techniques for modulation of the dysbiotic oral microbiome that may help in disease prevention and treatment, including standard hygiene methods, prebiotics, probiotics, use of nano-sized drug delivery systems (nano-DDS), extracellular polymeric matrix (EPM) disruption, and host response modulators.

Competition and Caries on Enamel of a Dual-Species Biofilm Model with Streptococcus mutans and Streptococcus sanguinis

Imbalances within the dental biofilm trigger dental caries, currently considered a dysbiosis and the most prevalent noncommunicable disease. There is still a gap in knowledge about the dynamics of enamel colonization by bacteria from the dental biofilm in caries. The aim, therefore, was to test whether the sequence of enamel colonization by a typically commensal and a cariogenic species modifies biofilm's cariogenicity. Dual-species biofilms of Streptococcus mutans and Streptococcus sanguinis on saliva-coated enamel slabs were inoculated in different sequences: S. mutans followed by S. sanguinis (Sm-Ss), S. sanguinis followed by S. mutans (Ss-Sm), S. mutans and S. sanguinis inoculated at the same time (Sm=Ss), and the single-species controls S. mutans followed by S. mutans (Sm-Sm) and S. sanguinis followed by S. sanguinis (Ss-Ss). Biofilms were exposed to 10% sucrose 3 times per day for 5 days, and the slabs/biofilms were retrieved to assess demineralization, viable cells, biomass, proteins, polysaccharides, and H₂O₂ production. Compared with Sm-Sm, primary inoculation with S. sanguinis reduced demineralization (P < 0.05). Both Ss-Sm and Sm=Ss sequences showed reduction in biomass, protein, and polysaccharide content (P < 0.05). The highest S. sanguinis viable count and H₂O₂ production level and the lowest acidogenicity were observed when S. sanguinis colonized enamel before S. mutans (P < 0.05). Initial enamel adherence with commensal biofilms seems to induce more intense competition against more typically cariogenic species, reducing cariogenicity.IMPORTANCE The concept of caries as an ecological disease implies the understanding of the intricate relationships among the populating microorganisms. Under frequent sugar exposure, some bacteria from the dental biofilm develop pathogenic traits that lead to imbalances (dysbiosis). Depending on which microorganism colonizes the dental surface first, different competition strategies may be developed. Studying the interactions in the entire dental biofilm is not an easy task. In this study, therefore, we modeled the interplay among these microorganisms using a caries-inducing species (S. mutans) and a health-associated species (S. sanguinis). Initial enamel adherence with S. sanguinis seems to induce more intense competition against typically caries-inducing species. Besides continuous exposure with sugars, early colonization of the enamel by highly cariogenic species like S. mutans appears to be needed to develop caries lesions as well. Promoting early colonization by health-associated bacteria such as S. sanguinis could help to maintain oral health, delaying dysbiosis.

When to intervene in the caries process? A Delphi consensus statement

Objectives To define an expert Delphi consensus on when to intervene in the caries process and existing carious lesions.Methods Non-systematic literature synthesis, expert Delphi consensus process and expert panel conference.Results Lesion activity, cavitation and cleansability determine intervention thresholds. Inactive lesions do not require treatment (in some cases, restorations may be placed for form, function, aesthetics); active lesions do. Non-cavitated carious lesions should be managed non- or micro-invasively, as should most cavitated lesions which are cleansable. Cavitated lesions which are not cleansable usually require minimally invasive management. In specific circumstances, mixed interventions may be applicable. Occlusally, cavitated lesions confined to enamel/non-cavitated lesions extending radiographically into deep dentine may be exceptions. Proximally, cavitation is hard to assess tactile-visually. Most lesions extending radiographically into the middle/inner third of dentine are assumed to be cavitated. Those restricted to the enamel are not cavitated. For lesions extending radiographically into the outer third of dentine, cavitation is unlikely. These lesions should be managed as if they were non-cavitated unless otherwise indicated. Individual decisions should consider factors modifying these thresholds.Conclusions Comprehensive diagnosis is the basis for systematic decision-making on when to intervene in the caries process and existing lesions.

Measuring Streptococcus mutans, Streptococcus sanguinis and Candida albicans biofilm formation using a real-time impedance-based system

Candida albicans and streptococci are amongst the most common fungal and bacterial organisms present in the oral cavity, with a growing body of evidence implicating C. albicans in increased caries severity and in the formation of the cariogenic biofilm. However, the interactive mechanisms between cariogenic streptococci and Candida are yet to be elucidated. In this study, the real-time biofilm formation of C. albicans, S. mutans and S. sanguinis was assessed individually and in combination using the xCELLigence system, an impedance-based microbial biofilm monitoring system. The impedance signal was the highest for C. albicans, followed by S. mutans and S. sanguinis. Although the streptococcal mixed adhesion was found to follow a similar trend to that of S. sanguinis, the introduction of C. albicans resulted in higher adhesion patterns, with the combined growth of S. sanguinis and C. albicans and the combination of all three species resulting in higher biofilm formation than any of the individual organisms over time. This study, the first to use impedance for real-time monitoring of interkingdom biofilms, adds to the body of evidence that C. albicans and oral streptococcal adhesion are interlinked and suggests that interkingdom interactions induce changes in the oral biofilm dynamics over time.

Exposure of Streptococcus mutans and Streptococcus sanguinis to blue light in an oral biofilm model

The potential anti-cariogenic effect of blue light was evaluated using an oral biofilm model. Two species, Streptococcus mutans and Streptococcus sanguinis, were cultivated ex vivo on bovine enamel blocks for 24 h, either separately or mixed together, then exposed to blue light (wavelengths 400-500 nm) using 112 J/cm². Twenty four or 48 h after exposure to light the biofilm structure and biomass were characterized and quantified using SEM and qPCR, respectively. Bacterial viability was analyzed by CLSM using live/dead bacterial staining. Gene expression was examined by RT-qPCR. After exposure to light, S. mutans biomass in mono-species biofilm was increased mainly by dead bacteria, relative to control. However, the bacterial biomass of S. mutans when grown in mixed biofilm and of S. sanguinis in mono-species biofilm was reduced after light exposure, with no significant change in viability when compared to control. Furthermore, when grown separately, an upregulation of gene expression related to biofilm formation of S. mutans, and downregulation of similar genes of S. sanguinis, were measured 24 h after exposure to blue light. However, in mixed biofilm, a downregulation of those genes in both species was observed, although not significant in S. mutans. In conclusion, blue light seems to effectively alter the bacterial biomass by reducing the viability and virulence characteristics in both bacterial species and may promote the anti-cariogenic balance between them, when grown in a mixed biofilm. Therefore, exposure of oral biofilm to blue light has the potential to serve as a complementary approach in preventive dentistry.

Effects of Norspermidine on Dual-Species Biofilms Composed of Streptococcus mutans and Streptococcus sanguinis

The present study aimed at investigating the influence of norspermidine on the formation of dual-species biofilms composed of Streptococcus mutans (S. mutans) and Streptococcus sanguinis (S. sanguinis). Crystal violet assay was conducted to assess the formation of single-species biofilms of S. mutans and S. sanguinis, and the growth curve was carefully observed to monitor the growth of these two species of bacteria. Fluorescence in situ hybridization (FISH) and MTT array were used to analyze the composition and metabolic activity of the dual-species biofilms, respectively. Extracellular polysaccharides (EPS)/bacteria staining, anthrone method, and scanning electron microscopy (SEM) imaging were conducted to study the synthesis of EPS by dual-species biofilms. Lactic acid assay and pH were measured to detect dual-species biofilm acid production. We found that norspermidine had different effects on S. mutans and S. sanguinis including their growth and biofilm formation. Norspermidine regulated the composition of the dual-species biofilms, decreased the ratio of S. mutans in dual-species biofilms, and reduced the metabolic activity, EPS synthesis, and acid production of dual-species biofilms. Norspermidine regulated dual-species biofilms in an ecological way, suggesting that it may be a potent reagent for controlling dental biofilms and managing dental caries.

When to intervene in the caries process? An expert Delphi consensus statement

OBJECTIVES

To define an expert Delphi consensus on when to intervene in the caries process and on existing carious lesions using non- or micro-invasive, invasive/restorative or mixed interventions.

METHODS

Non-systematic literature synthesis, expert Delphi consensus process and expert panel conference.

RESULTS

Carious lesion activity, cavitation and cleansability determine intervention thresholds. Inactive lesions do not require treatment (in some cases, restorations will be placed for reasons of form, function and aesthetics); active lesions do. Non-cavitated carious lesions should be managed non- or micro-invasively, as should most cavitated carious lesions which are cleansable. Cavitated lesions which are not cleansable usually require invasive/restorative management, to restore form, function and aesthetics. In specific circumstances, mixed interventions may be applicable. On occlusal surfaces, cavitated lesions confined to enamel and non-cavitated lesions radiographically extending deep into dentine (middle or inner dentine third, D2/3) may be exceptions to that rule. On proximal surfaces, cavitation is hard to assess visually or by using tactile methods. Hence, radiographic lesion depth is used to determine the likelihood of cavitation. Most lesions radiographically extending into the middle or inner third of the dentine (D2/3) can be assumed to be cavitated, while those restricted to the enamel (E1/2) are not cavitated. For lesions radiographically extending into the outer third of the dentine (D1), cavitation is unlikely, and these lesions should be managed as if they were non-cavitated unless otherwise indicated. Individual decisions should consider factors modifying these thresholds.

CONCLUSIONS

Comprehensive diagnostics are the basis for systematic decision-making on when to intervene in the caries process and on existing carious lesions.

CLINICAL RELEVANCE

Carious lesion activity, cavitation and cleansability determine intervention thresholds. Invasive treatments should be applied restrictively and with these factors in mind.

The effect of smoking on caries-related microorganisms

INTRODUCTION

Epidemiological studies have shown a close relationship between smoking and dental caries. Bacteria are one of the essential factors of caries formation. The imbalance of cariogenic bacteria and commensal bacteria in dental plaque results in higher production of acid that can corrode dental hard tissue. The aim of our review is to summarize the effect of smoking on caries-related bacteria.

METHODS

English articles available in Pubmed and ScienceDirect databases and published before December 2018 were searched. A variety of evidence was collected including not only the influence of cigarette products on bacteria strains in vitro but also their effect on bacterial composition in saliva and dental plaque in vivo. We particularly emphasize the mechanisms by which nicotine acts on oral bacteria.

RESULTS

The components of cigarettes promote the growth of cariogenic microorganisms. The mechanisms of how nicotine enhances Streptococcus mutans, Lactobacilli, Streptococcus gordonii, Actinomyces and Candida albicans are described separately in detail. The commensal bacteria, Streptococcus sanguinis, show less competitive capability in the presence of nicotine. Smoking influences saliva by lowering the buffer capability, altering its chemical agent and bacterial components, and therefore promotes the formation of a caries-susceptible environment.

CONCLUSIONS

Cigarette smoking and nicotine exposure promote the cariogenic activity of oral microorganisms and the formation of a caries-susceptible environment. This suggests that smokers should quit smoking, amongst other health reasons, also for their oral health.

Anticaries activity of egg ovalbumin in an experimental caries biofilm model on enamel and dentin

OBJECTIVES

Limited evidence suggests a putative inhibitory effect of dietary proteins on demineralization during the carious process. The aim was to explore a potential anticaries activity of the egg protein ovalbumin on a relevant in vitro approach.

MATERIALS AND METHODS

Biofilms of Streptococcus mutans UA159 were formed on saliva-coated enamel and dentin bovine slabs. Biofilms were challenged with 10% sucrose followed by either a 200 μg/mL solution of ovalbumin or 1:10, 1:100, and 1:1000 (v/v) serial dilutions of that ovalbumin solution, for the entire length of the experiment. Biofilms exposed to 10% sucrose followed only by 0.9% NaCl served as caries-positive control. Once completed the experimental phase, biofilms were analyzed for biomass, viable bacteria, and polysaccharide formation. Final surface hardness (SH) was obtained to calculate %SH loss (demineralization). Two independent experiments were conducted, in triplicate. Data were analyzed by ANOVA and a post hoc test at the 95% confidence level.

RESULTS

A reduction (p < 0.05) in biomass and extracellular polysaccharide formation, but not in the number of viable cells, was observed for both dental substrates. All ovalbumin concentrations tested showed lower demineralization than the positive control (p < 0.05), in a dose-dependent manner. The highest concentration showed a reduction in the %SH loss of about 30% for both enamel and dentin.

CONCLUSION

Egg ovalbumin presented to sucrose-challenged biofilms of Streptococcus mutans seems to reduce cariogenicity of a biofilm-caries model.

CLINICAL RELEVANCE

Ovalbumin may counteract the cariogenic effect of sugars. If these findings are clinically confirmed, novel preventive approaches for caries are warranted.

Streptococcus sanguinis biofilm formation & interaction with oral pathogens

Caries and periodontitis are the two most common human dental diseases and are caused by dysbiosis of oral flora. Although commensal microorganisms have been demonstrated to protect against pathogens and promote oral health, most previous studies have addressed pathogenesis rather than commensalism. Streptococcus sanguinis is a commensal bacterium that is abundant in the oral biofilm and whose presence is correlated with health. Here, we focus on the mechanism of biofilm formation in S. sanguinis and the interaction of S. sanguinis with caries- and periodontitis-associated pathogens. In addition, since S. sanguinis is well known as a cause of infective endocarditis, we discuss the relationship between S. sanguinis biofilm formation and its pathogenicity in endocarditis.