A multi-station dental plaque microcosm (artificial mouth) for the study of plaque growth, metabolism, pH, and mineralization

Evaluating models and assessment techniques for understanding oral biofilm complexity

Oral biofilms are three-dimensional (3D) complex entities initiating dental diseases and have been evaluated extensively in the scientific literature using several biofilm models and assessment techniques. The list of biofilm models and assessment techniques may overwhelm a novice biofilm researcher. This narrative review aims to summarize the existing literature on biofilm models and assessment techniques, providing additional information on selecting an appropriate model and corresponding assessment techniques, which may be useful as a guide to the beginner biofilm investigator and as a refresher to experienced researchers. The review addresses previously established 2D models, outlining their advantages and limitations based on the growth environment, availability of nutrients, and the number of bacterial species, while also exploring novel 3D biofilm models. The growth of biofilms on clinically relevant 3D models, particularly melt electrowritten fibrous scaffolds, is discussed with a specific focus that has not been previously reported. Relevant studies on validated oral microcosm models that have recently gaining prominence are summarized. The review analyses the advantages and limitations of biofilm assessment methods, including colony forming unit culture, crystal violet, 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt assays, confocal microscopy, fluorescence in situ hybridization, scanning electron microscopy, quantitative polymerase chain reaction, and next-generation sequencing. The use of more complex models with advanced assessment methodologies, subject to the availability of equipment/facilities, may help in developing clinically relevant biofilms and answering appropriate research questions.

Fabrication and characterization of a 3D polymicrobial microcosm biofilm model using melt electrowritten scaffolds

The majority of current biofilm models or substrates are two-dimensional (2D) and support biofilm growth in the horizontal plane only. Three-dimensional (3D) substrates may support both horizontal and vertical biofilm growth. This study compared biofilm growth quantity and quality between highly porous 3D micrometric fibrous scaffolds and 2D film substrates fabricated from medical grade polycaprolactone (mPCL). Melt electrowriting (MEW), a high-resolution additive manufacturing technology, was employed to design orderly aligned fine (~12 μm) fibre-based 3D scaffolds, while 2D films were fabricated by a casting method. The 3D scaffolds with a controlled pore size of 100 and 250 μm and thickness of ~0.8 mm and 2D films were incubated in pooled saliva collected from six volunteers for 1, 2, 4, 7 and 10 days at 37 °C to facilitate polymicrobial biofilm formation. Crystal violet assay demonstrated greater biofilm biomass in 3D MEW scaffolds than in 2D films. Biofilm thickness in 3D scaffolds was significantly higher compared to the biofilm thickness in 2D films. Both biovolume and substratum coverage of the biofilms was higher in the 3D scaffolds compared to 2D films. Polymeric bridges, pores, and channels characteristic of biofilms could be demonstrated by scanning electron microscopy. 16S rRNA sequencing demonstrated that the polymicrobial biofilms in the 3D scaffolds were able to retain 60-70 % of the original inoculum microbiome after 4 days. The MEW-fabricated 3D fibrous scaffold is a promising substrate for supporting multidirectional biofilm growth and modelling of a polymicrobial microcosm.

Oral Microcosm Biofilms Grown under Conditions Progressing from Peri-Implant Health, Peri-Implant Mucositis, and Peri-Implantitis

Peri-implantitis is a disease influenced by dysbiotic microbial communities that play a role in the short- and long-term outcomes of its clinical treatment. The ecological triggers that establish the progression from peri-implant mucositis to peri-implantitis remain unknown. This investigation describes the development of a novel in vitro microcosm biofilm model. Biofilms were grown over 30 days over machined titanium discs in a constant depth film fermentor (CDFF), which was inoculated (I) with pooled human saliva. Following longitudinal biofilm sampling across peri-implant health (PH), peri-implant mucositis (PM), and peri-implantitis (PI) conditions, the characterisation of the biofilms was performed. The biofilm analyses included imaging by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), selective and non-selective culture media of viable biofilms, and 16S rRNA gene amplification and sequencing. Bacterial qualitative shifts were observed by CLSM and SEM across conditions, which were defined by characteristic phenotypes. A total of 9 phyla, 83 genera, and 156 species were identified throughout the experiment. The phyla Proteobacteria, Bacteroidetes, Firmicutes, Fusobacteria, and Actinobacteria showed the highest prevalence in PI conditions. This novel in vitro microcosm model provides a high-throughput alternative for growing microcosm biofilms resembling an in vitro progression from PH-PM-PI conditions.

Caries-inhibiting Effect of Microencapsulated Active Components in Pit and Fissure Sealants

OBJECTIVE

The aim of the present in vitro study was to examine the caries-inhibiting effect of a pit and fissure sealant (PFS) containing ion-releasing microcapsules under cariogenic conditions in a biofilm artificial mouth.

METHODS AND MATERIALS

Forty-eight human third molars were divided into four groups (n=12 per group). Fissures were extended with burs and sealed with experimental PFS. The four groups of specimens were treated as follows: 1) EPFS 1: EPFS (Premier Dental) of increasing viscosity, containing microcapsules loaded with remineralizing agents (calcium, phosphate, and fluoride ions); 2) US: fluoride-releasing PFS (UltraSeal XT plus, UltraDent Products, South Jordan, UT, USA); 3) EPFS 2: experimental PFS of constant viscosity containing microcapsules loaded with calcium, phosphate, and fluoride ions; and 4) FT: glass ionomer cement (GIC) (GC Fuji Triage CAPSULE WHITE glass ionomer cement, GC Europe NV, Leuven, Belgium). FT and US were used as control groups. EPFS 1 and EPFS 2 were the experimental groups. Specimens were stored in distilled water for 14 days at 37°C, subjected to 10,000 thermocycles (5°C and 55°C) and finally exposed to microbiological cycling in a Streptococcus mutans-based artificial mouth for 10 days. Replicas were made for scanning electron microscopic (SEM) evaluation and specimens were cut for fluorescence microscopy.

RESULTS

Overall demineralization depths at the margin of Fuji Triage were significantly shallower than in the other groups (p<0.05). Overall demineralization depths adjacent to the experimental pit and fissure sealant EPFS 2 (59±15 μm) were comparable to the values of the resin-based pit and fissure sealant UltraSeal XT plus (58±10 μm, p≥0.05). SEM revealed surface roughness of the GIC-based PFS.

CONCLUSIONS

The experimental PFS with microcapsules containing active components for remineralization did not show a caries-inhibiting effect compared to a fluoride-releasing resin-based PFS. Lower demineralization depths adjacent to GIC sealants indicate an anticariogenic effect through fluoride ion release.

Biofilm reactor calibration for in vitro investigation of composite biodegradation

Introduction: The majority of biodegradation studies of composite materials use simplified models of microbial biofilm despite the apparent diversity of the oral microbiota. The use of in vitro systems of “artificial mouth” design is a step towards clarifying the synergistic effect that microbial plaque and human saliva have on composite degradation.

Aim: Establishment of functional parameters for in vitro reproduction of oral biofilms via biofilm reactor systems.

Materials and methods: The CDC Biofilm Reactor system consists of eight polypropylene sticks. The rod cover and the retaining plates are mounted in a 1-dm glass cylinder with an outlet side opening. The laboratory bioreactor has a working volume of 340 ml. The device is equipped with a four-blade magnetic stirrer. The system also includes gauging appliances and executive mechanisms for controlling and adjusting the basic parameters of the process.

Results: Determination of the operating volume of the reactor is performed prior to the experiment along with the time of reach and stabilization of the set temperature in the design which is 60 min at 120 rpm. A mathematical model is used to calculate the rate of delivery of growth medium - 11 millilitres per minute. The bioreactor is sterilized by 0.3% neomycin solution for 24 hours. Prior to the experiment the system is cleansed (via passage) with sterile water for 60 minutes.

Conclusions: The pre-calibration of a bioreactor system allows specification and refinement of its working parameters, thus engaging for accurate reproduction of the environmental conditions in the oral cavity.

In vitro model systems for exploring oral biofilms: From single-species populations to complex multi-species communities

Numerous in vitro biofilm model systems are available to study oral biofilms. Over the past several decades, increased understanding of oral biology and advances in technology have facilitated more accurate simulation of intraoral conditions and have allowed for the increased generalizability of in vitro oral biofilm studies. The integration of contemporary systems with confocal microscopy and 16S rRNA community profiling has enhanced the capabilities of in vitro biofilm model systems to quantify biofilm architecture and analyse microbial community composition. In this review, we describe several model systems relevant to modern in vitro oral biofilm studies: the constant depth film fermenter, Sorbarod perfusion system, drip-flow reactor, modified Robbins device, flowcells and microfluidic systems. We highlight how combining these systems with confocal microscopy and community composition analysis tools aids exploration of oral biofilm development under different conditions and in response to antimicrobial/anti-biofilm agents. The review closes with a discussion of future directions for the field of in vitro oral biofilm imaging and analysis.

An in vitro biofilm model system to facilitate study of microbial communities of the human oral cavity

The human oral cavity is host to a diverse microbiota. Much of what is known about the behaviour of oral microbes derives from studies of individual or several cultivated species, situations which do not totally reflect the function of organisms within more complex microbiota or multispecies biofilms. The number of validated models that allow examination of the role that biofilms play during oral cavity colonization is also limited. The CDC biofilm reactor is a standard method that has been deployed to study interactions between members of human microbiotas allowing studies to be completed during an extended period under conditions where nutrient availability, and washout of waste products are controlled. The objective of this work was to develop a robust in vitro biofilm-model system from a pooled saliva inoculum to study the development, reproducibility and stability of the oral microbiota. By employing deep sequencing of the variable regions of the 16S rRNA gene, we found that the CDC biofilm reactor could be used to efficiently cultivate microbiota containing all six major phyla previously identified as the core saliva microbiota. After an acclimatisation period, communities in each reactor stabilised. Replicate reactors were predominately populated by a shared core microbiota; variation between replicate reactors was primarily driven by shifts in abundance of shared operational taxonomic units. We conclude that the CDC biofilm reactor can be used to cultivate communities that replicate key features of the human oral cavity and is a useful tool to facilitate studies of the dynamics of these communities.

The impact of glass ionomer cement and composite resin on microscale pH in cariogenic biofilms and demineralization of dental tissues

OBJECTIVE

Secondary caries is among the most frequent reasons for the failure of dental restorations. Glass ionomer cement (GIC) restorations have been proposed to protect the surrounding dental tissues from demineralization through the release of fluoride and by buffering the acid attack from dental biofilms. In contrast, the lack of buffering by composite resin (CR) restorations has been suggested as a promoting factor for the development of secondary caries.

METHODS

The present study employed transversal microradiography and confocal microscopy based pH ratiometry to quantify mineral loss and map microscale pH gradients inside Streptococcus mutans biofilms grown on compound specimens consisting of enamel, dentin and either GIC or CR.

RESULTS

Mineral loss in dentin was significantly lower next to GIC than next to CR, but no significant differences in local biofilm pH were observed between the two restorative materials.

SIGNIFICANCE

The cariostatic effect of GIC relies predominantly on the provision of fluoride and not on a direct buffering action. The lack of buffering by CR did not affect local biofilm pH and may therefore be of minor importance for secondary caries development.

Mimicking biofilm formation and development: Recent progress in in vitro and in vivo biofilm models

Biofilm formation in living organisms is associated to tissue and implant infections, and it has also been linked to the contribution of antibiotic resistance. Thus, understanding biofilm development and being able to mimic such processes is vital for the successful development of antibiofilm treatments and therapies. Several decades of research have contributed to building the foundation for developing in vitro and in vivo biofilm models. However, no such thing as an "all fit" in vitro or in vivo biofilm models is currently available. In this review, in addition to presenting an updated overview of biofilm formation, we critically revise recent approaches for the improvement of in vitro and in vivo biofilm models.

Root Caries Preventive Effect of Varnishes Containing Fluoride or Fluoride + Chlorhexidine/Cetylpyridinium Chloride In Vitro

Caries preventive varnishes containing only fluoride might differ from those containing a combination of fluoride and antimicrobial components in terms of mineralization properties and their impact on the cariogenic biofilm. We compared a fluoride and a fluoride + chlorhexidine (CHX)/cetylpyridinium chloride (CPC) varnish on root caries formation in vitro. One hundred bovine root dentin samples were allocated to five groups (n = 20/group): (1) 7700 ppm fluoride varnish (Fluorprotector S (F)), (2) experimental placebo varnish for F (F-P), (3) 1400 ppm fluoride + 0.3% CHX/0.5% CPC varnish (Cervitec F (CF)), (4) experimental placebo varnish for CF (CF-P), (5) untreated control. Cariogenic challenge was provided using a multi-station, continuous-culture 3-species (Streptococcus mutans (SM), Lactobacillus rhamnosus (LR), Actinomyces naeslundii (AN)) biofilm model for 10 days. Mineral loss (ΔZ) was evaluated using transversal microradiography and bacterial counts in the biofilm assessed as colony-forming units. Fluorescence in situ hybridization (FISH) and confocal microscopy were performed to assess the three-dimensional biofilm architecture. Mean ± SD (vol% × μm) ΔZ was significantly lower for F (9133 ± 758) and CF (9835 ± 1677) compared to control (11362 ± 919) (p < 0.05), without significant differences between F and CF. SM counts were significantly lower and LR counts significantly higher in F- and CF-biofilms compared to control. AN counts were significantly higher in the F-biofilms than in all other groups. According to FISH, SM and LR invaded dentinal tubules only in the control-group. In the CF-group, the basal biofilm layer did not contain SM and AN. Both F and CF varnishes had similar caries-preventive effects and a considerable impact on biofilm structure and composition.

Relevance of Biofilm Models in Periodontal Research: From Static to Dynamic Systems

Microbial biofilm modeling has improved in sophistication and scope, although only a limited number of standardized protocols are available. This review presents an example of a biofilm model, along with its evolution and application in studying periodontal and peri-implant diseases. In 2011, the ETEP (Etiology and Therapy of Periodontal and Peri-Implant Diseases) research group at the University Complutense of Madrid developed an in vitro biofilm static model using representative bacteria from the subgingival microbiota, demonstrating a pattern of bacterial colonization and maturation similar to in vivo subgingival biofilms. When the model and its methodology were standardized, the ETEP research group employed the validated in vitro biofilm model for testing in different applications. The evolution of this model is described in this manuscript, from the mere observation of biofilm growth and maturation on static models on hydroxyapatite or titanium discs, to the evaluation of the impact of dental implant surface composition and micro-structure using the dynamic biofilm model. This evolution was based on reproducing the ideal microenvironmental conditions for bacterial growth within a bioreactor and reaching the target surfaces using the fluid dynamics mimicking the salivary flow. The development of this relevant biofilm model has become a powerful tool to study the essential processes that regulate the formation and maturation of these important microbial communities, as well as their behavior when exposed to different antimicrobial compounds.

Development of a multispecies periodontal biofilm model within a stirred bioreactor

The objective of this work was to develop a subgingival biofilm model using a stirred bioreactor. Discs of bovine teeth were adapted to a stirred bioreactor filled with a culture medium containing bacterial species associated with periodontal health or disease. After anaerobic incubation, the biofilms growing on the substratum surfaces were collected and analyzed. The mean number of Colony-forming Units (CFUs) varied, but with no difference between 3 and 7 days of biofilm formation (p > 0.05). Scanning Electron Microscopy (SEM) analysis showed a uniform biofilm layer covering the cement layer of the root surface containing bacteria with diverse morphology. In checkerboard DNA-DNA hybridization, bacterial species were identified in both biofilms. In conclusion, a subgingival biofilm model was developed using a stirred bioreactor, allowing the in vitro reproduction of complex microbial communities. This is an advanced model that may be useful to mimic complex clinical periodontal biofilms.

Lipidomic profiling of non-mineralized dental plaque and biofilm by untargeted UHPLC-QTOF-MS/MS and SWATH acquisition

Dental plaque is a structurally organized biofilm which consists of diverse microbial colonies and extracellular matrix. Its composition may change when pathogenic microorganisms become dominating. Therefore, dental biofilm or plaque has been frequently investigated in the context of oral health and disease. Furthermore, its potential as an alternative matrix for analytical purposes has also been recognized in other disciplines like archeology, food sciences, and forensics. Thus, a careful in-depth characterization of dental plaque is worthwhile. Most of the conducted studies focused on the screening of microbial populations in dental plaque. Their lipid membranes, on the other hand, may significantly impact substance (metabolite) exchange within microbial colonies as well as xenobiotics uptake and incorporation into teeth. Under this umbrella, a comprehensive lipidomic profiling for determination of lipid compositions of in vivo dental plaque samples and of in vitro cultivated biofilm as surrogate matrix to be used for analytical purposes has been performed in this work. An untargeted lipidomics workflow utilizing a ultra-high-performance liquid chromatography (UHPLC)-quadrupole-time-of-flight (QTOF) platform together with comprehensive SWATH (sequential window acquisition of all theoretical fragment ion mass spectra) acquisition and compatible software (MS-DIAL) that comprises a vast lipid library has been adopted to establish an extensive lipidomic fingerprint of dental plaque. The main lipid components in dental plaque were identified as triacylglycerols, followed by cholesterol, cholesteryl esters as well as diacylglycerols, and various phospholipid classes. In vivo plaque is a rare matrix which is usually available in very low amounts. When higher quantities for specific research assays are required, efficient ways to produce an appropriate surrogate matrix are mandatory. A potential surrogate matrix substituting dental plaque was prepared by cultivation of in vitro biofilm from saliva and similarities and differences in the lipidomics profile to in vivo plaque were mapped by statistical evaluation post-analysis. It was discovered that most lipid classes were highly elevated in the in vitro biofilm samples, in particular diacylglycerols, phosphatidylglycerols, and phosphatidylethanolamines (PEs). Furthermore, an overall shift from even-chain lipid species to odd-chain lipids was observed in the cultivated biofilms. On the other hand, even-chain phosphatidylcholines (PCs), lysoPCs, cholesteryl esters, and cholesterol-sulfate were shown to be specifically increased in plaque samples.

Shockwave Therapy Efficiently Cures Multispecies Chronic Periodontitis in a Humanized Rat Model

Biofilms are ubiquitous in nature and are invariably associated with health and diseases of all living beings. Periodontal diseases & dental caries are the most prevalent conditions in which biofilm has established as a primary causative factor. Managing poly-microbial biofilm is the mainstay of periodontal therapy. Plethora of antimicrobials have been used till date to combat biofilm, but the emergence of antibiotic tolerance and resistance in biofilms is a major cause of concern. Apart from use of antimicrobials, various anti-biofilm strategies have evolved which include the use of mechanical, and chemical means to disrupt biofilms. However, none of these approaches have led to desired or optimal biofilm control and hence search for novel approach continues. Shockwaves are used in medical practice for various therapeutic purposes and in local drug delivery, gene therapy, wound healing & regeneration. With this background, a study was designed with an attempt to explore the possibility of using the shockwave for their effect on multispecies oral biofilm development from subgingival plaque samples obtained from chronic periodontitis patients. Plaque samples from 25 patients were used to derive multispecies biofilm which were used to check the efficacy of shockwaves and antibacterial efficacy of four clinically relevant antimicrobials. Biofilms were analyzed by scanning electron microscope; atomic force microscope and their biomass was quantitated by crystal violet staining. Further, a humanized rat model of periodontitis was developed. Patient derived plaque was used to establish periodontitis in healthy rats. The model was validated by performing colony forming unit (CFU) analysis of the infected tissue. The animals were subjected to low intensity shockwaves using a hand-held shockwave generator at the site of infection. Shockwave treatment was done with or without antimicrobial application. The animals were monitored for clearance of infection and for mortality. The results show that shockwave treatment in combination with antimicrobials is significantly effective in clearing a multispecies biofilm. This also brings out the possibility of application of shockwaves in the management of oral biofilms either alone or in combination with established antimicrobial agents. With further research, safety profile validation and clinical trials, shockwaves can be an effective, novel approach in management of biofilm associated periodontal disease.

Critical Appraisal of Oral Pre- and Probiotics for Caries Prevention and Care

In recent years, the concept of preventing caries-related microbial dysbiosis by enhancing the growth and survival of health-associated oral microbiota has emerged. In this article, the current evidence for the role of oral pre- and probiotics in caries prevention and caries management is discussed. Prebiotics are defined as "substrates that are selectively utilized by host microorganisms conferring a health benefit." With regard to caries, this would include alkali-generating substances such as urea and arginine, which are metabolized by some oral bacteria, resulting in ammonia production and increase in pH. While there is no evidence that urea added to chewing gums or mouth rinses significantly contributes to caries inhibition, multiple studies have shown that arginine in consumer products can exert an inhibitory effect on the caries process. Probiotics are "live microorganisms which when administrated in adequate amounts confer a health benefit on the host." Clinical trials have suggested that school-based programs with milk supplemented with probiotics and probiotic lozenges can reduce caries development in preschool children and in schoolchildren with high caries risk. Due to issues with research ethics (prebiotics) and risk of bias (prebiotics, probiotics), the confidence in the effect estimate is however limited. Further long-term clinical studies are needed with orally derived probiotic candidates, including the health-economic perspectives. In particular, the development and evaluation of oral synbiotic products, containing both prebiotics and a probiotic, would be of interest in the future management of dental caries.

Arrest of Root Carious Lesions via Sodium Fluoride, Chlorhexidine and Silver Diamine Fluoride In Vitro

OBJECTIVE

To compare the root carious lesion arrest of chlorhexidine (CHX) and silver diamine fluoride (SDF) varnishes and/or sodium fluoride rinses (NaF) in vitro.

BACKGROUND

Effective and easily applicable interventions for treating root carious lesions are needed, as these lesions are highly prevalent amongst elderly individuals.

METHODS

In 100 bovine dentin samples, artificial root carious lesions were induced using acetic acid and a continuous-culture Lactobacillus rhamnosus biofilm model. One quarter of each induced lesion was excavated and baseline dentinal bacterial counts assessed as Colony-Forming-Units (CFU) per mg. Samples were allocated to one of four treatments (n = 25/group): (1) untreated control; (2) 38% SDF or (3) 35% CHX varnish, each applied once, plus 500 ppm daily NaF rinse in the subsequent lesion progression phase; and (4) daily NaF rinses only. Samples were re-transferred to the biofilm model and submitted to a cariogenic challenge. After six days, another quarter of each lesion was used to assess bacterial counts and the remaining sample was used to assess integrated mineral loss (ΔZ) using microradiography.

RESULTS

ΔZ did not differ significantly between control (median (25th/75th percentiles): 9082 (7859/9782) vol % × µm), NaF (6704 (4507/9574) and SDF 7206 (5389/8082)) (p < 0.05/Kruskal-Wallis test). CHX significantly reduced ΔZ (3385 (2447/4496)) compared with all other groups (p < 0.05). Bacterial numbers did not differ significantly between control (1451 (875/2644) CFU/µg) and NaF (750 (260/1401)) (p > 0.05). SDF reduced bacterial counts (360 (136/1166)) significantly compared with control (p < 0.05). CHX reduced bacterial counts (190 (73/517)) significantly compared with NaF and control (p < 0.05).

CONCLUSION

CHX varnish plus regular NaF rinses arrested root carious lesions most successfully.

In vitro biofilm models to study dental caries: a systematic review

The aim of this systematic review is to characterize and discuss key methodological aspects of in vitro biofilm models for caries-related research and to verify the reproducibility and dose-response of models considering the response to anti-caries and/or antimicrobial substances. Inclusion criteria were divided into Part I (PI): an in vitro biofilm model that produces a cariogenic biofilm and/or caries-like lesions and allows pH fluctuations; and Part II (PII): models showing an effect of anti-caries and/or antimicrobial substances. Within PI, 72.9% consisted of dynamic biofilm models, while 27.1% consisted of batch models. Within PII, 75.5% corresponded to dynamic models, whereas 24.5% corresponded to batch models. Respectively, 20.4 and 14.3% of the studies reported dose-response validations and reproducibility, and 32.7% were classified as having a high risk of bias. Several in vitro biofilm models are available for caries-related research; however, most models lack validation by dose-response and reproducibility experiments for each proposed protocol.

Full validation of a method for the determination of drugs of abuse in non-mineralized dental biofilm using liquid chromatography-tandem mass spectrometry and application to postmortem samples

Alternative matrices play a major role in postmortem forensic toxicology, especially if common matrices (like body fluids or hair) are not available. Incorporation of illicit and medicinal drugs into non-mineralized dental biofilm (plaque) seems likely but has not been investigated so far. Analysis of plaque could therefore extend the spectrum of potentially used matrices in postmortem toxicology. For this reason, a rapid, simple and sensitive method for the extraction, determination and quantification of ten drugs of abuse from plaque using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and fully validated. Amphetamine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxy-N-ethylamphetamine (MDEA), 3,4-methylenedioxyamphetamine (MDA), cocaine, benzoylecgonine, morphine, codeine and 6-acetylmorphine were extracted from 2mg of dried and powdered plaque via ultrasonication with acetonitrile. The extracts were analyzed on a triple-quadrupole linear ion trap mass spectrometer in scheduled multiple reaction monitoring mode (sMRM). The method was fully validated and proved accurate, precise, selective and specific with satisfactory linearity within the calibrated ranges. The lower limit of quantification was 10-15pgmg^-1 for all compounds except for MDA (100pgmg^-1) and amphetamine (200pgmg^-1). The method has been successfully applied to three authentic postmortem samples with known drug history. Amphetamine, MDMA, cocaine, benzoylecgonine, morphine and codeine could be detected in these cases in concentrations ranging from 18pgmg^-1 for cocaine to 1400pgmg^-1 for amphetamine.

Dental Biofilm and Laboratory Microbial Culture Models for Cariology Research

Dental caries form through a complex interaction over time among dental plaque, fermentable carbohydrate, and host factors (including teeth and saliva). As a key factor, dental plaque or biofilm substantially influence the characteristic of the carious lesions. Laboratory microbial culture models are often used because they provide a controllable and constant environment for cariology research. Moreover, they do not have ethical problems associated with clinical studies. The design of the microbial culture model varies from simple to sophisticated according to the purpose of the investigation. Each model is a compromise between the reality of the oral cavity and the simplification of the model. Researchers, however, can still obtain meaningful and useful results from the models they select. Laboratory microbial culture models can be categorized into a closed system and an open system. Models in the closed system have a finite supply of nutrients, and are also simple and cost-effective. Models in the open system enabled the supply of a fresh culture medium and the removal of metabolites and spent culture liquid simultaneously. They provide better regulation of the biofilm growth rate than the models in the closed system. This review paper gives an overview of the dental plaque biofilm and laboratory microbial culture models used for cariology research.

Inhibition of Streptococcus mutans Growth and Biofilm Formation by Probiotics in vitro

To exert anticaries effects, probiotics are described to inhibit growth and biofilm formation of cariogenic bacteria such as Streptococcus mutans (SM). We screened 8 probiotics and assessed how SM growth or biofilm formation inhibition affects cariogenicity of probiotic-SM mixed-species biofilms in vitro. Growth inhibition was assessed by cocultivating probiotics and 2 SM strains (ATCC 20532/25175) on agar. Probiotics were either precultured before SM cultivation (exclusion), or SM precultured prior to probiotic cultivation (displacement). Inhibition of SM culture growth was assessed visually. Inhibition of SM biofilm formation on bovine enamel was assessed using a continuous-flow short-term biofilm model, again in exclusion or displacement mode. The cariogenicity of mixed-species biofilms of SM with the most promising growth and biofilm formation inhibiting probiotic strains was assessed using an artificial mouth model, and enamel mineral loss (ΔZ) was measured microradiographically. We found limited differences in SM growth inhibition in exclusion versus displacement mode, and in inhibition of SM 20532 versus 25175. Results were therefore pooled. Lactobacillus acidophilus LA-5 inhibited significantly more SM culture growth than most other probiotics. L. casei LC-11 inhibited SM biofilm formation similarly to other alternatives but showed the highest retention of probiotics in the biofilms (p < 0.05). Mineral loss from SM monospecies biofilms (ΔZ = 9,772, 25th/75th percentiles: 6,277/13,558 vol% × µm) was significantly lower than from mixed-species SM × LA-5 biofilms (ΔZ = 24,578, 25th/75th percentiles: 19,081/28,768 vol% × µm; p < 0.01) but significantly higher than from SM × LC-11 biofilms (ΔZ = 4,835, 25th/75th percentiles: 263/7,865 vol% × µm; p < 0.05). Probiotics inhibiting SM culture growth do not necessarily reduce the cariogenicity of SM-probiotic biofilms. Nevertheless, SM biofilm formation inhibition may be relevant in the reduction of cariogenicity.

The Role of Microbiology in Models of Dental Caries: Reaction Paper

Models of the caries process have made significant contributions toward defining the roles of bacteria in caries. Microbiologists use a variety of in vitro systems to model aspects of the caries process. Also, in situ models in humans provide information on the microbiology of caries in vivo. These models do not involve the entire process leading to natural caries; consequently, the results from such studies are used to deduce the roles of bacteria in natural caries. Therefore, they can be described as Inferential Caries Models. In contrast, animal models and some clinical trials in humans involve natural caries and can be described as Complete Caries Models. Furthermore, these models are used in two distinct ways. They can be used as Exploratory Models to explore different aspects of the caries process, or as Test Models to determine the effects of anticaries agents. This dichotomy in approach to the use of caries models results in modification of the models to suit a particular role. For example, if we consider Exploratory Models, the in situ appliance in humans is superior to others for analyzing the microbiology of plaque development and demineralization in vivo. The chemostat and biofilm models are excellent for exploring factors influencing bacterial interactions. Both models can also be used as Test Models. The in situ model has been used to test the effects of fluoride on the microflora and demineralization, while the chemostat and biofilm models allow for the testing of antibacterial agents. Each model has its advantages and disadvantages and role in analysis of the caries process. Selection of the model depends on the scientific question posed and the limitations imposed by the conditions available for the study.

Nitrate and the Origin of Saliva Influence Composition and Short Chain Fatty Acid Production of Oral Microcosms

Nitrate is emerging as a possible health benefactor. Especially the microbial conversion of nitrate to nitrite in the oral cavity and the subsequent conversion to nitric oxide in the stomach are of interest in this regard. Yet, how nitrate influences the composition and biochemistry of the oral ecosystem is not fully understood. To investigate the effect of nitrate on oral ecology, we performed a 4-week experiment using the multiplaque artificial mouth (MAM) biofilm model. This model was inoculated with stimulated saliva of two healthy donors. Half of the microcosms (n = 4) received a constant supply of nitrate, while the other half functioned as control (n = 4). Additionally, all microcosms received a nitrate and sucrose pulse, each week, on separate days to measure nitrate reduction and acid formation. The bacterial composition of the microcosms was determined by 16S rDNA sequencing. The origin of the saliva (i.e., donor) showed to be the strongest determinant for the development of the microcosms. The supplementation of nitrate was related to a relatively high abundance of Neisseria in the microcosms of both donors, while Veillonella was highly abundant in the nitrate-supplemented microcosms of only one of the donors. The lactate concentration after sucrose addition was similarly high in all microcosms, irrespective of treatment or donor, while the concentration of butyrate was lower after nitrate addition in the nitrate-receiving microcosms. In conclusion, nitrate influences the composition and biochemistry of oral microcosms, although the result is strongly dependent on the inoculum.

Efficacy of dental unit waterlines disinfectants on a polymicrobial biofilm

Due to their high surface-volume ratio, their laminar flow and frequent stagnation periods, dental unit waterlines (DUWL) foster the attachment of microorganisms and the development of biofilm, resulting in the continuous contamination of the outlet water from dental units; this contamination may be responsible for a potential risk of infection due to the exposure of patients and medical staff to droplet inhalation or splashed water. In this study, the anti-biofilm activity of three disinfectants recommended by dental unit manufacturers -Calbenium(©), Oxygenal 6(©) and Sterispray(©) - was evaluated. A dynamic model simulating DUWL conditions was developed and polymicrobial biofilms containing bacteria (Pseudomonas aeruginosa), fungi (Candida albicans) and Free Living Amoeba (FLA: Vermamoeba vermiformis) were allowed to form. The ability of disinfectants to reduce biofilm formation or to eradicate an already formed biofilm was evaluated. Results showed the various effects of the tested disinfectants according to their composition, concentration and the targeted species. V. vermiformis was resistant to disinfectants, regardless of the tested concentrations and the concentrations recommended by manufacturers were not the most appropriate. Results also showed that Calbenium(©) was the most effective disinfectant to reduce already formed biofilms; its maximum efficiency was observed from 0.5% on both P. aeruginosa and C. albicans compared to 2 and 3% respectively for Sterispray(©). The maximum efficiency of Oxygenal(©) was observed from 3% on P. aeruginosa but Oxygenal(©) was unable to totally eliminate C. albicans in the tested conditions, contrary to other disinfectants. Calbenium(©) was able to prevent biofilm formation efficiently even if it displayed no prophylactic activity against V. vermiformis. Overall, the FLA survival may contribute to maintaining other species. Finally the tested disinfectants were partially active against sessile microorganisms and more suitable concentrations could be used to increase their efficacy. Their use in a prophylactic rather than curative way should be recommended.

An in vitro dynamic microcosm biofilm model for caries lesion development and antimicrobial dose-response studies

Some dynamic biofilm models for dental caries development are limited as they require multiple experiments and do not allow independent biofilm growth units, making them expensive and time-consuming. This study aimed to develop and test an in vitro dynamic microcosm biofilm model for caries lesion development and for dose-response to chlorhexidine. Microcosm biofilms were grown under two different protocols from saliva on bovine enamel discs for up to 21 days. The study outcomes were as follows: the percentage of enamel surface hardness change, integrated hardness loss, and the CFU counts from the biofilms formed. The measured outcomes, mineral loss and CFU counts showed dose-response effects as a result of the treatment with chlorhexidine. Overall, the findings suggest that biofilm growth for seven days with 0.06 ml min(-1) salivary flow under exposure to 5% sucrose (3 × daily, 0.25 ml min(-1), 6 min) was suitable as a pre-clinical model for enamel demineralization and antimicrobial studies.

N-Acetyl-l-cysteine effects on multi-species oral biofilm formation and bacterial ecology

Future therapies for the treatment of dental decay have to consider the importance of preserving bacterial ecology while reducing biofilm adherence to teeth. A multi-species plaque-derived (MSPD) biofilm model was used to assess how concentrations of N-acetyl-l-cysteine (NAC) (0, 0·1, 1, 10%) affected the growth of complex oral biofilms. Biofilms were grown (n = 96) for 24 h on hydroxyapatite discs in BMM media with 0·5% sucrose. Bacterial viability and biomass formation was examined on each disc using a microtitre plate reader. In addition, fluorescence microscopy and Scanning Electron Microscopy was used to qualitatively examine the effect of NAC on bacterial biofilm aggregation, extracellular components and bacterial morphology. The total biomass was significantly decreased after exposure of both 1% (from 0·48, with a 95% confidence interval of (0·44, 0·57) to 0·35, with confidence interval (0·31, 0·38)) and 10% NAC (0·14 with confidence interval (0·11, 0·17)). 16S rRNA amplicon sequencing analysis indicated that 1% NAC reduced biofilm adherence while preserving biofilm ecology.

SIGNIFICANCE AND IMPACT OF THE STUDY

As a compound with a wide safety margin, N-acetyl-l-cysteine (NAC) has the potential to be used as a long term anti-plaque bacteriostatic agent for managing chronic dental decay without substantially altering biofilm's bacterial ecology. The potential anti-caries benefit of NAC is directly related to reducing the biofilm coverage which reduces the degree of acid generation and the amount of time that the surface is exposed to a lower pH.

Composition and development of oral bacterial communities

The oral bacterial microbiome encompasses approximately 700 commonly occurring phylotypes, approximately half of which can be present at any time in any individual. These bacteria are largely indigenous to the oral cavity; this limited habitat range suggests that interactions between the various phylotypes, and between the phylotypes and their environment, are crucial for their existence. Molecular cataloging has confirmed many basic observations on the composition of the oral microbiome that were formulated well before ribosomal RNA-based systematics, but the power and the scope of molecular taxonomy have resulted in the discovery of new phylotypes and, more importantly, have made possible a level of bacterial community analysis that was unachievable with classical methods. Bacterial community structure varies with location within the mouth, and changes in community structure are related to disease initiation and disease progression. Factors that influence the formation and the evolution of communities include selective adherence to epithelial or tooth surfaces, specific cell-to-cell binding as a driver of early community composition, and interorganismal interaction leading to alteration of the local environment, which represents the first step on the road to oral disease. A comprehensive understanding of how these factors interact to drive changes in the composition of the oral microbial community can lead to new strategies for the inhibition of periodontal diseases and dental caries.

Stability and resilience of oral microcosms toward acidification and Candida outgrowth by arginine supplementation

Dysbiosis induced by low pH in the oral ecosystem can lead to caries, a prevalent bacterial disease in humans. The amino acid arginine is one of the pH-elevating agents in the oral cavity. To obtain insights into the effect of arginine on oral microbial ecology, a multi-plaque "artificial mouth" (MAM) biofilm model was inoculated with saliva from a healthy volunteer and microcosms were grown for 4 weeks with 1.6 % (w/v) arginine supplement (Arginine) or without (Control), samples were taken at several time-points. A cariogenic environment was mimicked by sucrose pulsing. The bacterial composition was determined by 16S rRNA gene amplicon sequencing, the presence and amount of Candida and arginine deiminase system genes arcA and sagP by qPCR. Additionally, ammonium and short-chain fatty acid concentrations were determined. The Arginine microcosms were dominated by Streptococcus, Veillonella, and Neisseria and remained stable in time, while the composition of the Control microcosms diverged significantly in time, partially due to the presence of Megasphaera. The percentage of Candida increased 100-fold in the Control microcosms compared to the Arginine microcosms. The pH-raising effect of arginine was confirmed by the pH and ammonium results. The abundances of sagP and arcA were highest in the Arginine microcosms, while the concentration of butyrate was higher in the Control microcosms. We demonstrate that supplementation with arginine serves a health-promoting function; it enhances microcosm resilience toward acidification and suppresses outgrowth of the opportunistic pathogen Candida. Arginine facilitates stability of oral microbial communities and prevents them from becoming cariogenic.

An in vitro biofilm model system maintaining a highly reproducible species and metabolic diversity approaching that of the human oral microbiome

BACKGROUND

Our knowledge of microbial diversity in the human oral cavity has vastly expanded during the last two decades of research. However, much of what is known about the behavior of oral species to date derives from pure culture approaches and the studies combining several cultivated species, which likely does not fully reflect their function in complex microbial communities. It has been shown in studies with a limited number of cultivated species that early oral biofilm development occurs in a successional manner and that continuous low pH can lead to an enrichment of aciduric species. Observations that in vitro grown plaque biofilm microcosms can maintain similar pH profiles in response to carbohydrate addition as plaque in vivo suggests a complex microbial community can be established in the laboratory. In light of this, our primary goal was to develop a robust in vitro biofilm-model system from a pooled saliva inoculum in order to study the stability, reproducibility, and development of the oral microbiome, and its dynamic response to environmental changes from the community to the molecular level.

RESULTS

Comparative metagenomic analyses confirmed a high similarity of metabolic potential in biofilms to recently available oral metagenomes from healthy subjects as part of the Human Microbiome Project. A time-series metagenomic analysis of the taxonomic community composition in biofilms revealed that the proportions of major species at 3 hours of growth are maintained during 48 hours of biofilm development. By employing deep pyrosequencing of the 16S rRNA gene to investigate this biofilm model with regards to bacterial taxonomic diversity, we show a high reproducibility of the taxonomic carriage and proportions between: 1) individual biofilm samples; 2) biofilm batches grown at different dates; 3) DNA extraction techniques and 4) research laboratories.

CONCLUSIONS

Our study demonstrates that we now have the capability to grow stable oral microbial in vitro biofilms containing more than one hundred operational taxonomic units (OTU) which represent 60-80% of the original inoculum OTU richness. Previously uncultivated Human Oral Taxa (HOT) were identified in the biofilms and contributed to approximately one-third of the totally captured 16S rRNA gene diversity. To our knowledge, this represents the highest oral bacterial diversity reported for an in vitro model system so far. This robust model will help investigate currently uncultivated species and the known virulence properties for many oral pathogens not solely restricted to pure culture systems, but within multi-species biofilms.

Biofilm Formation on Composite Resins for Dental Restorations: An in Situ Study on the Effect of Chlorhexidine Mouthrinses

Purpose

Biofilm formation on the surface of dental restorative materials by oral bacteria is considered an important step in the development of secondary caries. The aim of this study was to evaluate the in situ effect of a chlorhexidine (CHX)-containing mouthrinse on the biofilm formation occurring on the surface of human enamel and of two resin-based commercially available materials: a silorane-based material (Filtek Silorane®) and a methacrylate-based material (Filtek Supreme XT®).

Methods

53 disks were obtained for each of the two composites and 37 disks for enamel. The surface was characterized by determining the surface roughness and the surface free energy of 5 samples for each of the three materials tested, then the remaining samples were mounted on splints worn by 16 volunteers. The participants were randomly divided into two groups: an experimental group that used 0.12% CHX-based mouthrinse and a control group that used a placebo mouthrinse. Biofilm formation on the different surfaces after a 24 h period was assessed using MTT assay.

Results

The two composites in the group treated with the placebo mouthrinse showed a similar biofilm formation, which was significantly higher than that occurring on enamel surfaces. The CHX-based mouthrinse significantly reduced biofilm formation on the surfaces of the two resin-based materials when compared with the placebo mouthrinse. The reduction was particularly relevant on the Filtek Silorane surfaces.

Conclusions

The new silorane-based material seems to interact with CHX in a promising way from the point of view of biofilm formation control.

A reproducible oral microcosm biofilm model for testing dental materials

AIMS

Most studies of biofilm effects on dental materials use single-species biofilms, or consortia. Microcosm biofilms grown directly from saliva or plaque are much more diverse, but difficult to characterize. We used the Human Oral Microbial Identification Microarray (HOMIM) to validate a reproducible oral microcosm model.

METHODS AND RESULTS

Saliva and dental plaque were collected from adults and children. Hydroxyapatite and dental composite discs were inoculated with either saliva or plaque, and microcosm biofilms were grown in a CDC biofilm reactor. In later experiments, the reactor was pulsed with sucrose. DNA from inoculums and microcosms was analysed by HOMIM for 272 species. Microcosms included about 60% of species from the original inoculum. Biofilms grown on hydroxyapatite and composites were extremely similar. Sucrose pulsing decreased diversity and pH, but increased the abundance of Streptococcus and Veillonella. Biofilms from the same donor, grown at different times, clustered together.

CONCLUSIONS

This model produced reproducible microcosm biofilms that were representative of the oral microbiota. Sucrose induced changes associated with dental caries.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first use of HOMIM to validate an oral microcosm model that can be used to study the effects of complex biofilms on dental materials.

An in vitro biofilm model for enamel demineralization and antimicrobial dose-response studies

Microcosm biofilms formed in microplates have demonstrated complex community dynamics similar to natural dental biofilm. No simplified microcosm models to evaluate enamel demineralization and dose-response effect to anticariogenic therapies have yet been established, thus this study was designed to develop a pre-clinical model fulfilling this purpose. Experiments were carried out to establish the time of biofilm formation and the sucrose concentration and exposure regimen. Biofilms were initiated from saliva and grown for up to 10 days on bovine enamel discs in 24-well plates, with a saliva analogue medium. Data were collected as pH readings and the percentage enamel surface hardness change. A dose-response evaluation was performed with chlorhexidine, which significantly affected the pH and mineral loss. Overall, the established model parameters, 5 days of biofilm growth with intermittent 1% sucrose exposure of 6 h per day, was suitable as a pre-clinical model for enamel demineralization and dose-response studies.

Using DGGE profiling to develop a novel culture medium suitable for oral microbial communities

More than 700 bacterial species have been detected in the human oral cavity. They form highly organized microbial communities and are responsible for many oral infectious diseases, such as dental caries and periodontal disease. The prevention and treatment of these diseases require a comprehensive knowledge of oral microbial communities, which largely relies on culture-dependent methods to provide detailed phenotypic and physiological analysis of these communities. However, most of the currently available laboratory media can only selectively support the growth of a limited number of bacterial species within these communities, and fail to sustain the original oral microbial diversity. In this study, using denaturing gradient gel electrophoresis (DGGE) as an index to systematically survey and analyse the selectivity of commonly used laboratory media, we developed a new medium (SHI medium) by combining the ingredients of several selected media that can support different subpopulations within the original oral microbial community derived from pooled saliva. DGGE and 454 pyrosequencing analysis showed that SHI medium was capable of supporting a more diversified community with a microbial profile closer to that of the original oral microbiota. Furthermore, 454 pyrosequencing revealed that SHI medium supported the growth of many oral species that have not before been cultured. Crystal violet assay and the confocal laser scanning microscope analysis indicated that, compared with other media, SHI medium is able to support a more complex saliva-derived biofilm with higher biomass yield and more diverse species. This DGGE-guided method could also be used to develop novel media for other complex microbial communities.

Streptococcus mutans, caries and simulation models

Dental caries and dental plaque are among the most common diseases worldwide, and are caused by a mixture of microorganisms and food debris. Specific types of acid-producing bacteria, especially Streptococcus mutans, colonize the dental surface and cause damage to the hard tooth structure in the presence of fermentable carbohydrates e.g., sucrose and fructose. This paper reviews the link between S. mutans and caries, as well as different simulation models that are available for studying caries. These models offer a valuable approach to study cariogenicity of different substrates as well as colonization of S. mutans.

Growing oral biofilms in a constant depth film fermentor (CDFF)

In order to grow organisms in such a manner as to mimic their physiological growth state in vivo, it is often desirable to grow them as biofilms in the laboratory. There are numerous systems available to accomplish this; however, some are more suited to the growth of oral biofilms (dental plaque) than others. The operating parameters of one such model, the constant depth film fermentor (CDFF), are given in this unit. This model is particularly suited to studying the varied biofilms which exist in the oral cavity because environmental factors such as the substratum, nutrient source, and gas flow can be altered.

Inhibition of biofilms associated with dentures and toothbrushes by tetrasodium EDTA

AIMS

We examined the efficacy of tetrasodium EDTA in eradicating biofilms derived from salivary inocula or pure cultures of Candida albicans on discs of polymethyl methacrylate (PMMA) denture base or on toothbrushes that had been used normally for 4-8 weeks. Its efficiency in virus neutralization was also determined.

METHODS AND RESULTS

Overnight (16 h) treatment with 4% (w/v) tetrasodium EDTA solution reduced salivary and C. albicans biofilm viable counts by > or =99%. Biofilm removal was confirmed using confocal laser scanning microscopy. Presence/absence of sucrose during biofilm formation had no effect on killing efficacy. Prolonged treatment of PMMA with tetrasodium EDTA did not influence subsequent formation of C. albicans biofilms or affect surface roughness of the PMMA, but it reduced subsequent biofilm formation from a salivary inoculum. Infectivities of herpes simplex virus and polio virus suspensions were reduced by >99.99% by treatment for 1 and 2 h, respectively.

CONCLUSIONS

Tetrasodium EDTA solution efficiently disinfected toothbrushes and PMMA discs, with the detachment of biofilms, and rapidly neutralized both nonenveloped and enveloped viruses.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dentures and toothbrushes become contaminated by bacterial biofilms and by viruses. There is a need for disinfection methods that are rapidly effective, cost-effective, nontoxic and easily implemented. These studies indicate that tetrasodium EDTA solution has disinfection applications in the oral care field.

Caries Inhibitory Activity of the Nano-HA In Vitro

The purpose of this study is to examine the inhibitory effects of nano-HA on the caries-inducing properties of a four-organism bacterial consortium in vitro. A series of in vitro anticarious experiments have been carried out by using a continuous culture system. Streptococcus mutans, Streptococcus sanguis, Actinomyces viscosus, Lactobacillus rhamnosus have been chosen as the experimental bacteria. After 48 hours, the dental plaque surface structure is observed with the scan electron microscope and the bacterial colonization was evaluated on dental plaque. The results show that Spherical nano-HA and mixed nano-HA are proved to be effective in anticarious experiments, and especially spherical nano-HA is more striking. It is able to damage the formation of biofilms (dental plaque), postpone or end the process of acid generation of bacteria metabolism. After 7 days, the demineralization of the enamel has been detected by using TEM. The spherical nano-HA might have a remineralization to early caries to prevent and decrease caries.

Microbiota of plaque microcosm biofilms: effect of three times daily sucrose pulses in different simulated oral environments

AIM

To explore the Ecological Plaque Hypothesis for dental caries. To test modification of the microbiota of dental plaque microcosm biofilms by sucrose pulsing during growth in two different simulated oral fluids, and with a urea-induced plaque pH elevation.

METHODS

Plaque microcosm biofilms were cultured in an 'artificial mouth' with and without 6-min 5% w/v sucrose pulses every 8 h in an environment of continuously supplied saliva-like defined medium with mucin (DMM), or basal medium mucin (BMM, a high-peptone-yeast extract oral fluid analogue), and also in DMM + 10 mmol/l urea, with sucrose pulsing. Forty plaque species were quantified by checkerboard DNA:DNA hybridization analysis.

RESULTS

Sucrose pulsing extended rapid plaque growth in DMM and BMM, inducing major microbiota changes in DMM but not in BMM. In DMM, some streptococci and lactobacilli were unaffected while others implicated in caries, together with Candida albicans and Capnocytophaga gingivalis, increased. Aerobic, microaerophilic and major anaerobic species decreased. Elevation of the pH(max) from 6.4 to 7.0 had almost no effect on the microbiota. BMM plaques were distinct from DMM plaques with particularly low levels of Candida albicans and Actinomyces.

CONCLUSIONS

Modest sucrose exposure in a saliva-like environment causes profound changes in the developmental self-organization of plaque microcosms, supporting the Ecological Plaque Hypothesis. Nevertheless, there is significant stability in microbial composition with varying pH near neutrality. Increases in levels of specific bacteria in response to sucrose could be characteristic of organisms particularly important in caries.

Human dental plaque microcosm biofilms: effect of nutrient variation on calcium phosphate deposition and growth

Plaque mineralisation is a multi-factorial process involving plaque pH, nucleation, inhibitors and promotors. It is poorly understood because of its complexity.

OBJECTIVE

To establish the effects of amino acids and peptones in the simulated oral fluid BMM, a saliva analogue DMM and modifications of these on mineral deposition into dental plaque biofilm microcosms.

METHODS

Microcosms were cultured for up to 35 days in an Artificial Mouth pulsed with sucrose, followed by 10 days periodic treatment with a pH 5.0 calcium-phosphate-monofluorophosphate-urea solution (CPMU).

RESULTS

Initial biofilm doubling times were 3-7h, which then slowed and varied under the different nutrient conditions although their pH behaviour was similar. In BMM, mineral deposition was 20% that of DMM, but removal of BMM peptones increased deposition 12-fold. Substitution of the amino acids in DMM by casein did not affect deposition levels, but their removal leaving mucin the sole macronutrient, increased mineral deposition three-fold, reaching 40 mmol Ca/g protein.

CONCLUSIONS

These substantial increases in mineral deposition when the macronutrient concentration is reduced indicates probable changes in the nucleating, inhibitory and Ca-binding properties of the simulated oral fluids themselves and/or changes in the plaque microbiota and their crystal nucleators and inhibitors.

Individual microflora beget unique oral microcosms

AIMS

To examine the efficacy of the multiple Sorbarod device (MSD) for the reproduction of inter-individual variations in oral microbiotas. The MSD supports sessile growth on parallel cellulose filters, perfused with artificial saliva. This enables biofilms (BF) to be grown and sampled, together with released cells in eluted medium (perfusates, PAs).

METHODS AND RESULTS

Two sets of triplicate MSDs were established. One set was inoculated using fresh saliva from three separate volunteers; the second set was inoculated from one saliva donor. Both were incubated in an anaerobic cabinet. BF and PA were analysed at 24-h intervals by PCR-denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. Hierarchical dendrograms were constructed in order to sort community fingerprints over time, based on community relatedness. The MSD supported complex oral communities, as evidenced by DGGE (>20 distinct DGGE bands) and confocal scanning laser microscopy. DGGE band sequencing revealed bacteriological diversity and a high incidence of anaerobic species, including Prevotella sp. Dendrograms demonstrated marked inter-individual variation in the relative species abundance within salivary inocula from different volunteers (DV) and each associated MSD (all >45%, majority c. 85% concordance). Less variation was shown between triplicate models established using saliva from a single volunteer (SV) (all >58%; majority c. 95% concordance). PAs clustered together with the associated biofilms and inocula in the majority of cases for the DV MSDs whilst SV MSD community profiles clustered between replicate MSDs.

CONCLUSIONS

Data indicate that marked inter-individual variations in human salivary composition can be partially replicated in individualized MSD microcosms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the in vitro reproduction of individual oral microbiotas and suggests that taking inter-individual variability into account will increase the relevance of microcosm studies.

Up-regulation of competence- but not stress-responsive proteins accompanies an altered metabolic phenotype in Streptococcus mutans biofilms

Mature biofilm and planktonic cells of Streptococcus mutans cultured in a neutral pH environment were subjected to comparative proteome analysis. Of the 242 protein spots identified, 48 were significantly altered in their level of expression (P<0.050) or were unique to planktonic or biofilm-grown cells. Among these were four hypothetical proteins as well as proteins known to be associated with the maintenance of competence or found to possess a cin-box-like element upstream of their coding gene. Most notable among the non-responsive genes were those encoding the molecular chaperones DnaK, GroEL and GroES, which are considered to be up-regulated by sessile growth. Analysis of the rest of the proteome indicated that a number of cellular functions associated with carbon uptake and cell division were down-regulated. The data obtained were consistent with the hypothesis that a reduction in the general growth rate of mature biofilms of S. mutans in a neutral pH environment is associated with the maintenance of transformation without the concomitant stress response observed during the transient state of competence in bacterial batch cultures.