Constant Depth Film Fermentor Research Articles

Anti-biofilm activity of zinc oxide and hydroxyapatite nanoparticles as dental implant coating materials

ObjectivesDental implants are prone to failure as a result of bacterial biofilm accumulation. Such biofilms are often resistant to traditional antimicrobials and the use of nanoparticles as implant coatings may offer a means to control infection over a prolonged period. The objective of this study was to determine the antibiofilm activity of nanoparticulate coated titanium (Ti) discs using a film fermenter based system. MethodsMetal oxide nanoparticles of zinc oxide (nZnO), hydroxyapatite (nHA) and a combination (nZnO+nHA) were coated using electrohydrodynamic deposition onto Ti discs. Using human saliva as an inoculum, biofilms were grown on coated discs for 96h in a constant depth film fermenter under aerobic conditions with artificial saliva and peri-implant sulcular fluid. Viability assays and biofilm thickness measurements were used to assess antimicrobial activity. ResultsFollowing 96h, reduced numbers of facultatively anaerobic and Streptococcus spp. on all three nano-coated surfaces were demonstrated. The proportion of non-viable microorganisms was shown to be higher on nZnO and composite (nZnO+nHA) coated surfaces at 96h compared with nHA coated and uncoated titanium. Biofilm thickness comparison also demonstrated that nZnO and composite coatings to be the most effective. ConclusionsThe findings support the use of coating Ti dental implant surfaces with nZnO to provide an antimicrobial function. Clinical significanceCurrent forms of treatment for implant associated infection are often inadequate and may result in chronic infection requiring implant removal and resective/regenerative procedures to restore and reshape supporting tissue. The use of metal oxide nanoparticles to coat implants could provide osteoconductive and antimicrobial functionalities to prevent failure.

Physical disruption of oral biofilms by sodium bicarbonate: an invitro study.

Sodium bicarbonate has been shown clinically to be efficacious at removing dental plaque; however, its effect of mechanism against biofilms has not been evaluated invitro. Here, we used a well-established invitro plaque biofilm model to investigate the disruption of dental plaque biofilms. Biofilms were grown in a constant depth film fermentor for up to 14days. The fermentor was inoculated with pooled human saliva and growth maintained with artificial saliva. After various time points, replicate biofilms were removed and subjected to treatment at varying concentrations of sodium bicarbonate. Disruption of the plaque was assessed by viable counts and microscopy. The viable count results showed that younger biofilms were less susceptible to the action of sodium bicarbonate; however, biofilms of 7days and older were increasingly susceptible to the material with the oldest biofilms being the most susceptible. Sixty-seven percentage of sodium bicarbonate slurry was able to reduce the number of organisms present by approx. 3 log10 . These quantitative data were corroborated qualitatively with both confocal and electron microscopy, which both showed substantial qualitative removal of mature biofilms. The results from this study have shown that sodium bicarbonate is able to disrupt mature dental plaque grown invitro and that its reported efficacy in maintaining oral hygiene may be related to this key factor.

The influence of surface roughness and surface dynamics on the attachment of Methicillin-Resistant Staphylococcus aureus onto orthodontic retainer materials.

Staphylococci species have been isolated from removable orthodontic retainers. The aims of this study were to determine the most suitable device to analyze surface roughness of autopolymerized acrylic and thermoplastic materials and whether the surface dynamics of these materials influences the attachment of Methicillin-Resistant Staphylococcus aureus (MRSA). Clinically simulated samples of autopolymerized acrylic and thermoplastic material were first evaluated using laser non-contact, stylus mechanical profilometries and atomic force microscopy (AFM) followed by contact angle measurement to characterize their surface dynamics. Finally, an in vitro biofilm assay was carried out using a constant depth film fermentor to assess biofilm attachment. The results showed a significant difference between the roughness values obtained from the tested profilometers with the AFM exhibiting the most consistent roughness values. MRSA tended to accumulate initially within the microscopic irregularities of autopolymerized acrylic samples whereas acid-base and electron donor interactions influenced the bacterial attachment onto the thermoplastic samples.

Reproducible Biofilm Cultivation of Chemostat-Grown Escherichia coli and Investigation of Bacterial Adhesion on Biomaterials Using a Non-Constant-Depth Film Fermenter

Biomaterials-associated infections are primarily initiated by the adhesion of microorganisms on the biomaterial surfaces and subsequent biofilm formation. Understanding the fundamental microbial adhesion mechanisms and biofilm development is crucial for developing strategies to prevent such infections. Suitable in vitro systems for biofilm cultivation and bacterial adhesion at controllable, constant and reproducible conditions are indispensable. This study aimed (i) to modify the previously described constant-depth film fermenter for the reproducible cultivation of biofilms at non-depth-restricted, constant and low shear conditions and (ii) to use this system to elucidate bacterial adhesion kinetics on different biomaterials, focusing on biomaterials surface nanoroughness and hydrophobicity. Chemostat-grown Escherichia coli were used for biofilm cultivation on titanium oxide and investigating bacterial adhesion over time on titanium oxide, poly(styrene), poly(tetrafluoroethylene) and glass. Using chemostat-grown microbial cells (single-species continuous culture) minimized variations between the biofilms cultivated during different experimental runs. Bacterial adhesion on biomaterials comprised an initial lag-phase I followed by a fast adhesion phase II and a phase of saturation III. With increasing biomaterials surface nanoroughness and increasing hydrophobicity, adhesion rates increased during phases I and II. The influence of materials surface hydrophobicity seemed to exceed that of nanoroughness during the lag-phase I, whereas it was vice versa during adhesion phase II. This study introduces the non-constant-depth film fermenter in combination with a chemostat culture to allow for a controlled approach to reproducibly cultivate biofilms and to investigate bacterial adhesion kinetics at constant and low shear conditions. The findings will support developing and adequate testing of biomaterials surface modifications eventually preventing biomaterial-associated infections.

Antibacterial effect of gallium and silver on Pseudomonas aeruginosa treated with gallium–silver–phosphate-based glasses

Gallium and silver incorporated phosphate-based glasses were evaluated for antibacterial effect on the growth of Pseudomonas aeruginosa, which is a leading cause of opportunistic infections. The glasses were produced by conventional melt quenching methods at 1100°C for 1 h. Glass degradation studies were conducted by weight loss method. Disc diffusion assay and cell viability assay displayed statistically significant (p ≤ 0.0005) effect on P. aeruginosa growth which increased with decreasing calcium content in the glasses. The gallium ion release rates (1.83, 0.69 and 0.48 ppm·h(-1)) and silver ion release rates (2.97, 2.84 and 2.47 ppm·h(-1)) were found to account for this variation. Constant depth film fermentor was used to evaluate the anti-biofilm properties of the glasses. Both gallium and silver in the glass contributed to biofilm growth inhibitory effect on P. aeruginosa (up to 2.68 reduction in log 10 values of the viable counts compared with controls). The glasses were found to deliver gallium and silver in a controlled way and exerted cumulative antibacterial action on planktonic and biofilm growth of P. aeruginosa. The antibacterial, especially anti-biofilm, properties of the gallium and silver incorporated phosphate-based glasses make them a potential candidate to combat infections caused by P. aeruginosa.

Effect of Gallium on Growth of Streptococcus mutans NCTC 10449 and Dental Tissues

Gallium-doped phosphate-based glasses (Ga-PBG) were assessed for their impact on Streptococcus mutans and dental mineralisation, firstly by disc diffusion assays followed by biofilms grown on nitrocellulose filter membrane (NFM) and constant-depth film fermentor (CDFF). Short-time exposure (10 min) effects of Ga-PBG on S. mutans biofilm were compared with that of 0.2% chlorhexidine. The effects of Ga-PBG on bovine enamel (which was investigated under pH-cycling condition) and dentine were analysed using transverse microradiography (TMR), profilometry and inductively coupled plasma optical-emission spectrometry (ICP-OES). The disc diffusion assays showed inhibition zones of 24.5 ± 0.5 mm for Ga-PBG compared with controls (C-PBG). Ga-PBG showed statistically significant growth inhibition of S. mutans biofilms on NFM (p = 0.001) and CDFF (p < 0.046) compared with hydroxyapatite (HA) and C-PBG. The CDFF assay revealed a maximum of 2.11 log colony-forming unit (CFU) reduction at 48 h, but short-time exposure effects were comparable with that of 0.2% chlorhexidine only on older biofilms (maximum of 0.59 vs. 0.69 log CFU reduction at 120 h). TMR analyses of the enamel revealed non-significant mineral loss (p = 0.37) only in the case of Ga-PBG samples compared with controls including sodium fluoride. ICP-OES analyses indicated transient gallium adsorption into dentine by calcium displacement. The results confirmed that gallium inhibited S. mutans growth and appears to have the potential to protect the enamel surface under conditions representative of the oral environment. Further work is needed to establish whether it has an application in daily oral hygiene procedures to prevent or reduce caries.

Essential Oils and Zirconia Dental Implant Materials

This study was conducted to evaluate the effectiveness of natural antimicrobial agents in reducing biofilm development on different titanium and zirconia dental implant materials in vitro using a constant depth film fermentor (CDFF). Contact angles and surface free energy were determined for all surfaces. Biofilms were grown on disks of polished partially stabilized zirconia, titanium blasted with zirconia, titanium blasted with zirconia and acid-etched, and polished titanium using a CDFF to simulate oral cavity conditions. Antimicrobials (cinnamon oil, clove oil, chlorhexidine gluconate, or 0.5% Tween 80) were pulsed twice daily to the biofilm to mimic application in the oral cavity. Samples were taken after 6, 24, and 48 hours. Serial dilutions were made and plated onto agar. Bacterial colonies were counted to determine colony-forming units/mL. Treatment of different implant material surfaces with the various antimicrobial agents led to significant increases in wettability and free energy on all surfaces. All surfaces showed a remarkable decrease in bacterial adhesion in the first 2 days in a relatively similar manner, with significant reduction in most of them, particularly after 48 hours. Functionalization of different dental implant material surfaces with essential oils resulted in immediate and ongoing antibacterial and antiplaque activities, and this antibacterial effect was enhanced with increased plaque age. Differences in the type of material seemed to have little effect on bacterial adhesion after treatment with antimicrobial agents. Expansion of this work with in vivo studies and clinical trials would be valuable.

Novel amelogenin-releasing hydrogel for remineralization of enamel artificial caries.

Recently, the use of recombinant full-length amelogenin protein in combination with fluoride has shown promising results in the formation of densely packed enamel-like structures. In this study, amelogenin (rP172)-releasing hydrogels containing calcium, phosphate, and fluoride were investigated for remineralization efficacy using in vitro early enamel caries models. The hydrogels were applied to artificial caries lesions on extracted human third molars, and the remineralization efficacy was tested in different models: static gel remineralization in the presence of artificial saliva, pH cyclic treatment at pH 5.4 acetic buffer and pH 7.3 gel remineralization, and treatment with multispecies oral biofilms grown in a continuous flowing constant-depth film fermenter. The surface microhardness of remineralized enamel increased significantly when amelogenin was released from hydrogel. No cytotoxicity was observed when periodontal ligament cells were cultured with the mineralized hydrogels.

Reducing the variability between constant-depth film fermenter experiments when modelling oral biofilm

The inherent instabilities associated with the development of multispecies biofilm communities within the constant-depth film fermenter (CDFF) and other microcosm systems can yield unacceptable variability between experiments, which could limit their potential applications in oral microbiology. The extent of this variability needs to be determined and a protocol developed which minimizes it. Two custom-made CDFFs were supplied concurrently with the same inoculation culture, begat from an aliquot of a saliva pool and artificial saliva growth medium via a dual-channel pump. Transformed log(10) data of the viable counts at fixed time points were analysed using the Bland-Altman approach to test for the levels of agreement between two CDFFs running concurrently and those CDFFs run in series. The coefficients(95%) of agreement were lower (i.e. less variable) in the concurrent model than when run in series for total counts of bacteria (1.238 vs 2.124), Lactobacillus spp. (0.517 vs 1.431) and Mutans streptococci (2.817 vs 3.864). Other measures of variability showed a similar trend. Operating CDFFs concurrently minimizes the degree of difference and variability between them. Operating CDFFs concurrently will improve the sensitivity for experiments that seek to determine the effects of a variable, such as a nutritional supplement or antimicrobial agent, and a control.

Role of gallium and silver from phosphate-based glasses on in vitro dual species oral biofilm models of Porphyromonas gingivalis and Streptococcus gordonii

Phosphate-based glasses (PBGs) are excellent controlled delivery agents for antibacterial ions such as silver and gallium. The aim of this study was to assess the potential utility of novel PBGs combining both gallium and silver for use in periodontal therapy. To this end, an in vitro biofilm model with the putative periodontal pathogen, Porphyromonas gingivalis, and an initial colonizer, Streptococcus gordonii, was established. The effect of increasing calcium content in gallium–silver-doped PBG on the susceptibility of P. gingivalis was examined. A decrease in degradation rates (30.34, 25.19, 21.40μgmm−2h−1) with increasing PBG calciumcontent (10, 11, 12mol.% respectively) was observed, correlating well with gallium and silver ion release and antimicrobial activity against planktonic P. gingivalis (approximately 5.4log10 colony-forming units (CFU) reduction after 24h by the C10 glass compared with controls) and S. gordonii (total growth inhibition after 32h by C10, C11 and C12 glasses compared with controls). The most potent PBG (C10) was evaluated for its ability to inhibit the biofilm growth of P. gingivalis in a newly established constant-depth film fermentor model. The simultaneous release of silver and gallium from the glass reduced P. gingivalis biofilm growth with a maximum effect (1.92log10 CFU reduction) after 168h. Given the emergence of antibiotic-resistant bacteria and dearth of new antibiotics in development, the glasses, especially C10, would offer effective alternatives to antibiotics or may complement current therapies through controlled, localized delivery of gallium and silver ions at infected sites in the oral cavity.

In vitro interaction of chronic wound bacteria in biofilms

To use in vitro biofilm models of wound bacterial isolates and compare the biofilms produced for different combinations of wound bacterial species. In vitro biofilms, generated by Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus oralis and Micrococcus luteus in microtitre plates and a constant depth film fermentor (CDFF), were studied. The tested isolates all originated from chronic venous leg ulcers. Biofilms of individual and dual combinations of these species were generated in microtitre plate wells at 37°C for 24-96 hours and also in the CDFF for 7 days. The extent of biofilm formation from these systems was then measured using crystal violet staining and/or total viable counts. All the chronic wound bacteria formed biofilms (both individually and in mixed culture) in these models. In mixed species microtitre plate biofilms, both P. aeruginosa and S. aureus appeared to antagonise biofilm formation by S. oralis and M. luteus, with P. aeruginosa completely inhibiting the growth of these organisms. Similar effects were evident in the CDFF model, when all four bacterial species were added simultaneously, with M. luteus being 'out-competed' by the other organisms present and occurring at numbers at the limits of detection; however, there was an apparent increase in the numbers of S. oralis compared with its single culture equivalent. The study highlighted differences in biofilm formation ability for the tested species in both closed and open model systems. Using dual species biofilms, distinct species antagonism was observed with apparent antagonism of pathogenic species over 'commensal' ones. Such a finding provides insight into possible bacterial interactions during development of 'non-healing' wound biofilms.

In vitro assessment of shiitake mushroom (Lentinula edodes) extract for its antigingivitis activity.

Gingivitis is a preventable disease characterised by inflammation of the gums due to the buildup of a microbial biofilm at the gingival margin. It is implicated as a precursor to periodontitis, a much more serious problem which includes associated bone loss. Unfortunately, due to poor oral hygiene among the general population, gingivitis is prevalent and results in high treatment costs. Consequently, the option of treating gingivitis using functional foods, which promote oral health, is an attractive one. Medicinal mushrooms, including shiitake, have long been known for their immune system boosting as well as antimicrobial effects; however, they have not been employed in the treatment of oral disease. In the current study, the effectiveness of shiitake mushroom extract was compared to that of the active component in the leading gingivitis mouthwash, containing chlorhexidine, in an artificial mouth model (constant depth film fermenter). The total bacterial numbers as well as numbers of eight key taxa in the oral community were investigated over time using multiplex qPCR. The results indicated that shiitake mushroom extract lowered the numbers of some pathogenic taxa without affecting the taxa associated with health, unlike chlorhexidine which has a limited effect on all taxa.

The Effects of Fractions from Shiitake Mushroom on Composition and Cariogenicity of Dental Plaque Microcosms in an In Vitro Caries Model

The aim of the current study was to investigate the anticariogenic potential of the (sub)fractions obtained from the edible mushroom shiitake (Lentinula edodes) in in vitro caries model. We used a modified constant depth film fermentor (CDFF) with pooled saliva as the inoculum and bovine dentin as a substratum. The test compounds were low molecular weight fraction (MLMW) of the shiitake extract and subfractions 4 and 5 (SF4 and SF5) of this fraction. Chlorhexidine (CHX) and water served as a positive and a negative control, respectively. Dentin mineral loss was quantified (TMR), microbial shifts within the microcosms were determined (qPCR), and the acidogenicity of the microcosms was assessed (CIA). From the compounds tested, the SF4 of shiitake showed strong inhibiting effect on dentin demineralization and induced microbial shifts that could be associated with oral health. The acid producing potential was increased, suggesting uncoupling of the glycolysis of the microbiota by the exposure to SF4. In conclusion, the results suggest that SF4 of shiitake has an anticariogenic potential.

Transfer of antibiotic resistance by transformation with eDNA within oral biofilms

We demonstrate that live donor Veillonella dispar cells can transfer the conjugative transposon Tn916 to four different Streptococcus spp. recipients in a multispecies oral consortium growing as a biofilm in a constant depth film fermentor. Additionally, we demonstrate that purified V. dispar DNA can transform Streptococcus mitis to tetracycline resistance in this experimental system. These data show that transfer of conjugative transposon-encoded antibiotic resistance can occur by transformation in addition to conjugation in biofilms.

An in vitro model of chronic wound biofilms to test wound dressings and assess antimicrobial susceptibilities

The targeted disruption of biofilms in chronic wounds is an important treatment strategy and the subject of intense research. In the present study, an in vitro model of chronic wound biofilms was developed to assess the efficacy of antimicrobial treatments for use in the wound environment. Using chronic wound isolates, assays of bacterial coaggregation established that aerobic and anaerobic wound bacteria were able to coaggregate and form biofilms. A constant depth film fermenter (CDFF) was used to develop wound biofilms in vitro, which were analysed using light microscopy and scanning electron microscopy. The susceptibility of bacteria within these biofilms was examined in response to the most frequently prescribed 'chronic wound' antibiotics and a series of iodine- and silver-containing commercial antimicrobial products and lactoferrin. Defined biofilms were rapidly established within 1-2 days. Antibiotic treatment demonstrated that mixed Pseudomonas and Staphylococcus biofilms were not affected by ciprofloxacin (5 mg/L) or flucloxacillin (15 mg/L), even at concentrations equivalent to twice the observed peak serum levels. The results contrasted with the ability of povidone-iodine (1%) to disrupt the wound biofilm; an effect that was particularly pronounced in the dressing testing where iodine-based dressings completely disrupted established 7 day biofilms. In contrast, only two of six silver-containing dressings exhibited any effect on 3 day biofilms, with no effect on 7 day biofilms. This wound model emphasizes the potential role of the biofilm phenotype in the observed resistance to antibiotic therapies that may occur in chronic wounds in vivo.

Detection and identification of specific bacteria in wound biofilms using peptide nucleic acid fluorescent in situ hybridization (PNA FISH)

Biofilms provide a reservoir of potentially infectious micro-organisms that are resistant to antimicrobial agents, and their importance in the failure of medical devices and chronic inflammatory conditions is increasingly being recognized. Particular research interest exists in the association of biofilms with wound infection and non-healing, i.e. chronic wounds. In this study, fluorescent in situ hybridization (FISH) was used in combination with confocal laser scanning microscopy (CLSM) to detect and characterize the spatial distribution of biofilm-forming bacteria which predominate within human chronic skin wounds (Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus sp. and Micrococcus sp.). In vitro biofilms were prepared using a constant-depth film fermenter and a reconstituted human epidermis model. In vivo biofilms were also studied using biopsy samples from non-infected chronic venous leg ulcers. The specificity of peptide nucleic acid (PNA) probes for the target organisms was confirmed using mixed preparations of planktonic bacteria and multiplex PNA probing. Identification and location of individual bacterial species within multi-species biofilms demonstrated that P. aeruginosa was predominant. CLSM revealed clustering of individual species within mixed-species biofilms. FISH analysis of archive chronic wound biopsy sections showed bacterial presence and allowed bacterial load to be determined. The application of this standardized procedure makes available an assay for identification of single- or multi-species bacterial populations in tissue biopsies. The technique provides a reliable tool to study bacterial biofilm formation and offers an approach to assess targeted biofilm disruption strategies in vivo.

Relationship between Gap Size and Dentine Secondary Caries Formation Assessed in a Microcosm Biofilm Model

Secondary caries can develop at the tooth-restoration interface, depending on the presence of a gap and its size, but this process could be inhibited by fluoride. The aim of this study was to assess the relationship between gap size and dentine secondary caries adjacent to composite resin (CR) or glass ionomer (GI) restorations, using a microcosm biofilm model in a constant depth film fermentor (CDFF). Dentine discs restored with CR (Z250) or GI (Vitremer) with gap sizes of 0, 50, 100, 180 or 250 μm were mounted on the CDFF. Microcosm biofilms were formed on the restored discs and daily subjected to 8 pulses of 10% sucrose solution. On the 18th day, dentine mineral loss and lesion depth around the restorations were determined by transverse microradiography.The effect of gap size was overall not statistically significant either with regard to mineral loss (p = 0.449) or lesion depth (p = 0.328), but greater mineral loss and lesion depth were found adjacent to CR than to GI (p < 0.001). However, Spearman correlation showed that mineral loss and lesion depth increased with gap size for CR (p < 0.001) but not for GI (p > 0.05). The findings support the conclusion that fluoride released from GI inhibits dentine demineralization adjacent to restorations, irrespective of gap width.

The effect of conditioning films on colonization of root canal dentine by endodontic bacterial isolates

Aim To determine if conditioning films have an effect on the initial attachment of primary colonisers to root canal pre‐dentine.Methodology Noncarious, unrestored, extracted human teeth with single root canals were prepared to expose the pre‐dentine. Half of the samples (n = 50) were untreated (native), whilst the other half (n = 50) were treated with 2.5% NaOCl for 10 min and 17% EDTA for 2 min. The samples were then soaked in a designated conditioning solution; artificial saliva, human saliva, serum or blood for 90 min at 37 °C. The samples were then placed into a Constant Depth Film Fermentor and inoculated with either single [Streptococcus oralis (E01‐07‐008)] or dual species clinical isolates [S. oralis and Actinomyces naeslundii (E01‐07‐007)]. After 4 h, the samples were removed and prepared for SEM and viable counts to assess the bacterial attachment on their surfaces.Results Bacteria were observed on all samples when incubated with S. oralis. NaOCl/EDTA‐treated surfaces had less S. oralis colonization for all conditioning films. The number of bacteria ranged up to 4.4 × 104 CFU per sample; specimens not chemically treated but soaked in artificial saliva exhibited the most colonization. This was 17.4‐fold higher than the serum/chemically treated group. Colonization of specimens was over 90% lower with dual species than with a single isolate. Blood or serum‐treated surfaces had greater colonization (24‐fold difference in CFUs) for dual isolates than those treated with artificial saliva. Streptococcus oralis and A. naeslundii were capable of invading dentinal tubules within 4 h. Streptococcus oralis colonization was more common than that by A. naeslundii at the selected time interval. There was a random distribution of bacteria over the entire pre‐dentine surface but more bacterial attachment was observed in ‘secluded areas’ such as ‘giant tubules’, in voids in the conditioning film or around debris.Conclusions Bacterial colonization of pre‐dentine surfaces appeared to be influenced by species, surface pre‐treatment and conditioning agent.

Development of an in vitro denture plaque biofilm to model denture malodour

This study aimed to develop an in vitro denture plaque biofilm to model denture malodour. No previous studies have attempted to characterize the malodour associated with dentures and the effect of Candida spp. (main aetiological agent of denture-related stomatitis) on malodour. Pooled denture plaque microcosms and ‘model’ denture plaque biofilms (pooled saliva supplemented with additional microbial species) with and without addition of candida were grown aerobically at 37 °C for up to 13 days in a constant depth film fermenter (CDFF) on denture acrylic discs. Sample discs were removed, rinsed in sterile water and placed in phosphate buffered saline (PBS). The discs were vortex mixed to remove the biofilms, diluted in PBS and plated in duplicate onto general and selective media. The composition and stability of the biofilms over time were assessed. CDFF-grown microcosms and ‘model’ denture plaque biofilms were relatively stable in composition, with streptococci remaining the dominant microbial group. Model denture plaque biofilms were comparable in composition to denture plaque microcosms. This model system has the potential for evaluation of agents that might affect these parameters such as denture cleansers and other oral hygiene treatments.

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.