Cariogenic Flora Research Articles

The impact of probiotic supplementation on dental and general health metrics in pediatric populations

Relevance. Acute respiratory infections account for over 90% of infectious diseases in children. These children are classified as frequently ill, representing a significant concern in contemporary pediatrics. The presence of odontogenic infections further depletes their immunity and acts as a persistent source of sensitisation for the child's body.Materials and methods. A clinical-laboratory longitudinal prospective study was conducted on 477 children aged 12 and 15 years. The children were categorised into groups based on their risk of developing caries (minimal, moderate, high). Oral health status was assessed using the DMF index, oral hygiene was evaluated using the OHI-S index, and periodontal tissue condition was assessed using the PMA index. The activity of cariogenic flora aggression enzymes was measured by the level of salivary sialidase. The child's health status was evaluated using the infection index and the recurrence index. The schoolchildren were recommended a course of a preparation consisting of a combination of the probiotic Streptococcus salivarius M18 (at least 5 x 10^8 CFU) and vitamin D3 (320 IU or 8 µg of vitamin D3) at a dosage of one tablet per day, taken sublingually, for two months twice a year.Results. The study identified moderate correlations between salivary sialidase levels and several indicators, including the gingivitis index, the quantity of dental plaque, and the increase in sialidase activity in saliva. The level of salivary sialidase is regarded as a marker for plaque formation and the extent of periodontal tissue inflammation. Comprehensive oral sanitation, coupled with the strategic use of immunoprophylactic agents, resulted in significant improvements in oral health indicators (OHI-S, PMA, caries reduction) and specific child health metrics (infection index, recurrence index). Additionally, there was a notable reduction in salivary sialidase levels. The method demonstrated the highest efficacy in 12-year-old children who were at high risk of developing caries.Conclusion. The obtained data should be considered when planning individual therapeutic and preventive measures for schoolchildren with varying risks of developing caries and differing overall health statuses. Probiotic-based preparations should be incorporated into these measures.

Состояние микробиома десневой борозды детей с бронхиальной астмой

Aim. To compare the microbiome of the healthy gingival sulcus of children with bronchial asthma (BA) and different dental conditions. Design. Open comparative clinical and laboratory study. Materials and methods. Gingival substrate was obtained from 19 children aged 3–6 years with exacerbation of BA; the results of sequencing the genes of 16 subunits of ribosomal ribonucleic acid (16S rRNA) on the MiSeq platform (Illumina) were analyzed. Results. Five major phyla have been identified in the gingival sulcus: Firmicutes, Proteobacteria, Actinobacteria, Fusobacterium and Bacteroidetes and the dominant genus, Streptococcus. A significantly high relative prevalence of the species Neisseria oralis (p = 0.0073), Hemophilic massiliensis (p = 0.046), Hemophilic paraphrohaemolyticus (p = 0.05) and Lautropia mirabilis (p = 0.05) in children with asthma without caries was established. The level of immunoglobulin E (IgE) is significantly higher in children with asthma and caries compared to children without caries (461.79 ± 60.58 and 276.97 ± 81.15 IU/ml). Conclusion. The predominance of opportunistic and “healthy” bacterial species of the phylum Proteobacteria in the healthy gingival sulcus of children with BA may be an indicator of oral dysbiosis in BA. Overproduction of IgE in children with caries may be due to cariogenic flora, which requires further study. Keywords: sequencing, gingival crevicular microbiome, children, bronchial asthma, caries.

BRIX3000® Papain Gel for Cavity Treatment in the Adult Patient

Tooth decay is a multifactorial disease. Fermentable sugar, host factors, and cariogenic microbial flora are several agents that influence dental structure. In literature, alternative protocols for treating cavities are always of interest in terms of reducing pain and preserving tissue. In this case report, the use of a new gel-based on papain, which has a chemical effect on bacteria and allows the consistency of the altered tissue to be modified, leads to a less traumatic removal of the infected tissue. In this case report, BRIX3000, a gel with papain as its main ingredient, was used to treat an interproximal cavity on an upper premolar of a 35-year-old man frightened of the turbine. After a clinical check of all the systematic conditions and a first view of the oral cavity, the protocol was explained to the patient, and informed consent was obtained. The protocol involved applying the papain gel directly to the cavity, and after 2.5–3 minutes, it was removed. The complete removal of the infected tissue was achieved in three steps. The patient reported no discomfort, and the cavity was completely treated and ready to be restored. In conclusion, BRIX3000 seems to be a good alternative to the turbine in cavity treatment, particularly in patients who have discomfort during traditional treatments and are frightened of the turbine.

Nanosilver fluoride as a caries arresting agent: A narrative review

Dental caries is the most prevalent oral disease that continues to affect almost every country in the world. The contemporary management of dental caries focuses on non-restorative, non-invasive, and micro-invasive treatment approaches that arrest or reverse the caries process at a lesion level and reduce the loss of sound tooth structure. One of these approaches is the employment of caries arresting agents that possess antibacterial and remineralizing properties. Silver diamine fluoride (SDF) has drawn significant attention as an efficient caries arresting agent in children and adults. The major limitation with the use of SDF is the dark black staining of the carious tissue that compromises the esthetics. Silver ions are known for their antimicrobial effects, and silver nanoparticles (AgNPs) have the added advantage that it increases the surface area for exposure to the microbes. Literature reports that AgNPs have antimicrobial potential against predominant cariogenic flora. It has led to the development of nanosilver fluoride (NSF), a new colloid based on AgNPs, chitosan, and fluoride. It has shown to overcome the clinical limitations of SDF as it does not cause carious lesion staining. However, the current scientific literature lacks a comprehensive review of the benefits of using NSF for caries prevention and arrest. Thus, the purpose of this paper was to review the studies and clinical trials on NSF as a caries arresting agent, including antibacterial actions and modulation of the demineralization-remineralization balance.

Usnic acid deteriorates acidogenicity, acidurance and glucose metabolism of Streptococcus mutans through downregulation of two-component signal transduction systems

The principal etiological agent of human dental caries, Streptococcus mutans is a multi-virulent pathogen that can transform commensal oral microbial community to plaque biofilms. Major virulence factors that are associated with the cariogenicity of S. mutans include adhesion, acidogenicity and acidurity. All these pathogenic traits coordinate and alter the dental plaque ecology which provide room for interaction with other similar acidogenic and aciduric bacteria. This cariogenic flora increases the possibility of enamel demineralization which headway to caries development. The present study was aimed at evaluating the antimicrobial and antiinfective potential of a lichen secondary metabolite usnic acid (UA) against S. mutans. Minimum inhibitory concentration (MIC), Minimum bactericidal concentration (MBC) and growth kinetics were evaluated to determine the antimicrobial potential of UA against S. mutans. UA at 5 µg mL−1 and 10 µg mL−1 concentration were considered as MIC and MBC respectively. Effect on biofilm formation was microscopically assessed and found to be reduced in a concentration dependent manner. Gene expression of gtfB, gtfC, gtfD, vicR, ComDE and smu0630 was found to be downregulated upon treatment with sub-MIC of UA. Acidogenicity, acidurity, eDNA synthesis and response to oxidative stress were found to be attenuated by the influence of UA. It was also demonstrated to act on preformed mature biofilm of S. mutans. Moreover, UA was shown to possess very low frequency to acquire spontaneous resistance development in S. mutans. Besides, no morphological aberrations or toxic effect was instigated by UA in the human buccal epithelial cells as well as to the oral commensals. Altogether, these results demonstrate the therapeutic potential of usnic acid in the treatment of S. mutans infection.

Efficacy and Patient's Acceptance of Alternative Methods for Caries Removal-a Systematic Review.

Dental caries is a disease of dental hard tissues, considered the most common non-communicable disease worldwide. Conventional treatments for caries removal are often associated with pain and fear, so different therapeutic approaches have been developed towards more conservative and pleasant treatments. This systematic review aimed to assess the efficacy and patient’s acceptance of alternative methods for caries removal compared to conventional methods. The Cochrane Library, Embase, Medline/Pubmed, Web of Science, and Clinical Trials databases were searched. Clinical trials of primary dental caries treated with alternative methods were included. The last search was performed on 5 August 2020. The Population, Intervention, Comparison, and Outcome (PICO) strategy was followed. Thirty-seven clinical trials were included, reporting caries removal using alternative (chemomechanical—Brix 3000, Carie-care, Carisolv and Papacarie, laser—Er:YAG (Erbium-doped Yttrium Aluminium Garnet) and Er,Cr:YSGG (Erbium, Chromium-doped Yttrium, Scandium, Gallium and Garnet), and a system combining air and sono-abrasion—Vector® System) and conventional methods. Alternative methods tended to prolong treatment time and lessen anesthesia need. All treatments were effective in reducing cariogenic flora, and the restoration’s performance did not differ significantly. Chemomechanical solutions seemed to be the best option towards minimally invasive treatments, with good control during application and action and good treatment experiences for patients. Papacarie was demonstrated to be an effective method for caries removal with less pain, and superior acceptance by patients when compared to conventional treatments.

Clinical efficacy and the antimicrobial potential of silver formulations in arresting dental caries: a systematic review

BackgroundThe use of silver-formulation as microbicide to arrest dentinal caries is gaining popularity. The primary objective of the present appraisal was to systematically review the clinical (in vivo) applications and antimicrobial potential of silver-containing formulations in arresting dentinal caries. Our secondary aim was to sum up the available in vitro applications of silver-containing formulations against cariogenic microbes isolated from dentine lesions.MethodsOvid MEDLINE, EBSCO host, Web of Science, and Cochrane Library databases was searched between January 2009–May 2019.ResultsIn vivo: We observed conflicting evidence of antimicrobial efficacy of SDF on a diverse array of microbial taxa present in carious dentine of primary and permanent teeth. Moreover, there is insufficient evidence on the application of AgNP-fluoride as an effective microbicidal against cariogens of dentine lesions.In vitro: We found a good evidence of microbicidal efficacy of silver diamine fluoride (SDF) on selective cariogenic microbes in human dentine model. Additionally, a good evidence was noted of in vitro application of silver nanoparticles (AgNPs) as a useful microbicidal against S. mutans adhesion, growth and subsequent biofilm formation in human dentine models.ConclusionsTaken together, in vitro evidence indicates the promising antimicrobial potential of silver-based formulations (SDF and nanosilver) against the predominant cariogenic flora, particularly from dentine lesions. Post-treatment clinical data of either the bactericidal and bacteriostatic effects of SDF or nanosilver are sparse. Furthermore, the current understanding of the specific size, concentration, antimicrobial mechanisms, and toxicological aspects of nano-silver compounds is inadequate to draw firm conclusions on their clinical utility.

Assessment of antibacterial efficacy of ozone therapy in treatment of caries at the white spot stage

clinical and microbiological assessment of antibacterial efficacy of ozone therapy in treatment of caries at the white spot stage. The trial recruited 86 patients for non-invasive treatment of caries at the white spot stage which included the complex of professional oral hygiene, medicamental treatment of white spot lesions with hydrogen peroxide 3% and chlorhexidinedigluconate 0,2%, treatment with the ozone-air mixture and application of hydroxyapatite Са2+. Material for microbiological study was received before the treatment, after the complex of professional oral hygiene and medicamental treatment of white spot lesions conducted as well as after the treatment with the ozone-air mixture. Before the treatment up to 16 kinds of microorganisms on the surface of white spot lesion were detected with the following shares: S. mutans (19.9%), S. salivarius (15.1%), S. epidermidis (8.7%), S. mitis (6.5%), Lactobacillus (6.5%) and different kinds of staphylococci (10.8%). After the complex of professional oral hygiene and medicamental treatment conducted decrease in number of cariogenic microorganisms was indicated as follows: S. mutans - from 1·105 to 1·104, S. salivarius - from 1·107 to 1·106, S. epidermidis - from 1·105 to 1·104, S. mitis - from 1·104 to 1·103, Lactobacillus - from 1·104 tо 1·103. After the treatment of tooth enamel with the ozone-air mixture increase in microorganisms was not observed. The efficacy of ozone on cariogenic microorganisms exceeds significantly the efficacy of 3% hydrogen peroxide and 0,2% chlorhexidinedigluconate. It is strongly advisable to include ozone in protocol of non-invasive treatment of initial dental caries.

Comparison of the Efficacy of Chemomechanical Caries Removal (Papacarie - A Papain Gel) and Conventional Excavation in Reducing Cariogenic Flora: An In Vivo Study

Comparison of the Efficacy of Chemomechanical Caries Removal (Papacarie - A Papain Gel) and Conventional Excavation in Reducing Cariogenic Flora: An In Vivo Study

Acquired Oral Microflora of Newborns During the First 48 Hours of Life

To compare the oral microflora of a newborn during first hours after birth and after two days, and determine whether the newborn acquires his mother's microflora during this period. Saliva samples were taken from 50 newborns, on their first day of life, two days after, and from their mothers. Those samples were checked for total aerobic cultivated bacteria and mutans streptococci. Soon after birth, most newborns lacked any of the tested microorganisms in their oral cavity. Two days later, oral microorganisms were detected. A significant correlation was found between the total aerobic cultivated bacteria counts of the mothers, and of their newborns. It can be assumed, that on the first 48 hours of life, the newborn gains a major part of his oral microflora from his mother. These results might shade light on a possible to control and change the acquired microflora, at the very beginning of a human's life, creating a new, but less cariogenic flora. An accurate protocol should be examine to avoid this initial transmission during these days, while the mother and her newborn are still in the hospital, and thus might be possible to reduce caries prevalence in the future.

Efficacy of antimicrobial property of two commercially available chemomechanical caries removal agents (Carisolv and Papacarie): An ex vivo study.

Purpose:The purpose of the study is to evaluate the antimicrobial efficacy of Carisolv and Papacarie. There are only a few studies comparing the primary teeth. The objective of this study is to assess the effects of Carisolv and Papacarie on cariogenic flora and to compare them.Materials and Methods:Fifteen children aged 4–8 years who had at least two primary molars with broad occlusal cavitated lesions showing brown and softened dentin samples were selected. The selected 30 teeth were randomly divided into two groups of 15 teeth each for Carisolv and Papacarie. Dentin samples of both groups were taken prior to and following caries removal. The total viable count and lactobacilli count were determined and expressed as colony forming units per milliliter. The two methods of caries removal were then compared and the data were statistically analyzed.Results:The data of both agents (groups) were analyzed by Wilcoxon signed-rank test before and after application and showed statistical significance. Inter-comparison of data of both groups was analyzed by Mann–Whitney U test for total viable count and total Lactobacillus count which showed no statistical significance.Conclusion:Carisolv and Papacarie have similar antibacterial efficacy against cariogenic flora as chemomechanical caries removal agents.

Determination of theIn VitroandIn VivoAntimicrobial Activity on Salivary Streptococci and Lactobacilli and Chemical Characterisation of the Phenolic Content of aPlantago lanceolataInfusion

Introduction. Plant extracts may be suitable alternative treatments for caries. Aims. To investigate the in vitro and in vivo antimicrobial effects of Plantago lanceolata herbal tea (from flowers and leaves) on cariogenic bacteria and to identify the major constituents of P. lanceolata plant. Materials and Methods. The MIC and MBC against cariogenic bacteria were determined for P. lanceolata tea. Subsequently, a controlled random clinical study was conducted. Group A was instructed to rinse with a P. lanceolata mouth rinse, and Group B received a placebo mouth rinse for seven days. The salivary colonisation by streptococci and lactobacilli was investigated prior to treatment and on the fourth and seventh days. Finally, the P. lanceolata tea was analysed for its polyphenolic content, and major phenolics were identified. Results and Discussion. P. lanceolata teas demonstrate good in vitro antimicrobial activity. The in vivo test showed that Group A subjects presented a significant decrease in streptococci compared to Group B. The phytochemical analysis revealed that flavonoids, coumarins, lipids, cinnamic acids, lignans, and phenolic compounds are present in P. lanceolata infusions. Conclusions. P. lanceolata extract could represent a natural anticariogenic agent via an antimicrobial effect and might be useful as an ancillary measure to control the proliferation of cariogenic flora.

EARLY CHILDHOOD CARIES: CAN YOU PREVENT IT?

The probability of the caries development largely depends on the oral microflora imbalance. This imbalance can be corrected with probiotics. The article analyzes the results of studies on the use of adapted milk formulas with probiotics to prevent caries in early childhood. It shows that the use of adapted formulas with probiotics is accompanied by a decrease in the frequency of releasing cariogenic streptococci and actinomycetes with a simultaneous increase in the frequency of detecting bacterial antagonists of the cariogenic flora, normalization of sIgA concentration in saliva, and decrease in the severity of the caries process. The survey results will contribute to the development of effective approaches to prevention of dental caries in children.

A comparative in vitro efficacy of conventional rotatory and chemomechanical caries removal: Influence on cariogenic flora, microhardness, and residual composition.

Background:Chemomechanical caries removal system is part of the minimal invasive dentistry; the aim of the study was to compare the amount of bacteria after caries removal with chemomechanical system and conventional rotatory instruments and to test the Vickers microhardness and micro-RAMAN analysis of residual dentin after excavation.Materials and Methods:Molars were induced for demineralization, confirmed with DIAGNOdent; Streptococcus mutans were inoculated into the cavities and filled. Caries removal was performed with rotatory instruments and chemomechanical system; surviving bacteria were cultured for 24 and 48 hours at 37°C. Vickers microhardness and micro-RAMAN analysis were tested after excavation. Data were analyzed with Wilcoxon, continuity correction, odds ratio, ANOVA post hoc Tukey test, and Spearman correlation.Results:Demineralization was significantly detectable at 240 hours of incubation; conventional rotatory instruments and chemomechanical caries removal were effective in 19.4%-22.6% and 25.8%-32.3%, respectively. Vickers microhardness of chemomechanical system was higher (P < 0.0001) than conventional rotatory instruments and comparable to healthy dentin. Micro-RAMAN analysis showed that healthy dentin is correlated to chemomechanical system (R2 = 0.683, P < 0.00001) and drilling with burs (R2 = 0.139, P < 0.00001).Conclusion:The chemomechanical system is effective for caries elimination, comparable to conventional rotatory instruments; the remaining Vickers microhardness and composition surface tissue are similar to healthy dentin.

The virulence of Streptococcus mutans and the ability to form biofilms.

In some diseases, a very important role is played by the ability of bacteria to form multi-dimensional complex structure known as biofilm. The most common disease of the oral cavity, known as dental caries, is a top leader. Streptococcus mutans, one of the many etiological factors of dental caries, is a microorganism which is able to acquire new properties allowing for the expression of pathogenicity determinants determining its virulence in specific environmental conditions. Through the mechanism of adhesion to a solid surface, S. mutans is capable of colonizing the oral cavity and also of forming bacterial biofilm. Additional properties enabling S. mutans to colonize the oral cavity include the ability to survive in an acidic environment and specific interaction with other microorganisms colonizing this ecosystem. This review is an attempt to establish which characteristics associated with biofilm formation—virulence determinants of S. mutans—are responsible for the development of dental caries. In order to extend the knowledge of the nature of Streptococcus infections, an attempt to face the following problems will be made: Biofilm formation as a complex process of protein–bacterium interaction. To what extent do microorganisms of the cariogenic flora exemplified by S. mutans differ in virulence determinants “expression” from microorganisms of physiological flora? How does the environment of the oral cavity and its microorganisms affect the biofilm formation of dominant species? How do selected inhibitors affect the biofilm formation of cariogenic microorganisms?

Barnices Preventivos en Rehabilitación Oral

ObjectiveThe purpose of this preliminary study was to determine the influence of a single application of preventive varnishes over S. mutans and L. acidophilus flora, after oral rehabilitation and its correlation with the dental materials used. Methods33 patients (14 male and 19 female), ages 51-59 years (mean=57.8) bruxers, partially edentulous and removable prosthesis users were selected. They underwent full mouth restoration with composites resin reconstructions (CRR), fixed (PFM), removable and/or implanted prosthesis. After treatment all patients received oral hygiene instructions, including the use of interproximal brushes. Patients were randomly divided in 3 equal groups. Group A: Without any other preventive program; Group B: With one application of Duraphat® (Colgate-Palmolive); and Group C: With one application of Cervitec Plus ® (Ivoclar - Vivadent).Before (control) and 30 days after these applications (experimental), CRT bacteria® (Ivoclar- Vivadent) was applied. Data were statistically analyzed by the Mc Nemar Symmetry test and by the Kruscal-Wallis One -way test. ResultsCounts at Baseline/one month later of S. mutans p = 0,655 y L. acidophilus p =0,058. P values were: 0.864 for S. Mutans/PFM, 0.243 for S. Mutans/ CRR, 0.678 for Lactobacilli/ PFM and 0.440 for Lactobacilli/ CRR. ConclusionsIn full mouth restored patients, only one application of fluoride or clorhexidine varnishes did not affect the cariogenic flora after one month. There is no influence from PFM or CRR on bacterial counts.

Comparison of the Antimicrobial Efficacy of Chemomechanical Caries Removal (carisolv™) with that of Conventional Drilling in Reducing Cariogenic Flora

The aim of this study was to evaluate the antimicrobial efficacy of chemomechanical caries removal (Carisolv) in reducing the count of cariogenic flora and compare it to conventional drilling. The study group consisted of 20 healthy children aged between four and eight years. In each child, two primary molars with broad occlusal cavitated lesions were chosen for caries removal either with Carisolv or by conventional drilling. Dentin samples of both groups were taken prior to and following caries removal. They were then processed after suitable dilutions and cultured using Schaedler agar for the Total Viable Bacteria and MRS agar for the lactobacilli. After incubation at 35 degrees C for 3 days, the Total Viable Count and lactobacilli count was determined and expressed as Colony Forming Units per ml. The two methods of caries removal were then compared and the data was statistically analyzed. Both methods reduced the TVC count by 92% and lactobacilli count by 91%. RESULTS have indicated that the antimicrobial efficacy of Carisolv was comparable to that of conventional drilling and can be used as a suitable alternative for caries removal, especially in children.

Oral Health in Women During Preconception and Pregnancy: Implications for Birth Outcomes and Infant Oral Health

The mouth is an obvious portal of entry to the body, and oral health reflects and influences general health and well being. Maternal oral health has significant implications for birth outcomes and infant oral health. Maternal periodontal disease, that is, a chronic infection of the gingiva and supporting tooth structures, has been associated with preterm birth, development of preeclampsia, and delivery of a small-for-gestational age infant. Maternal oral flora is transmitted to the newborn infant, and increased cariogenic flora in the mother predisposes the infant to the development of caries. It is intriguing to consider preconception, pregnancy, or intrapartum treatment of oral health conditions as a mechanism to improve women's oral and general health, pregnancy outcomes, and their children's dental health. However, given the relationship between oral health and general health, oral health care should be a goal in its own right for all individuals. Regardless of the potential for improved oral health to improve pregnancy outcomes, public policies that support comprehensive dental services for vulnerable women of childbearing age should be expanded so that their own oral and general health is safeguarded and their children's risk of caries is reduced. Oral health promotion should include education of women and their health care providers ways to prevent oral disease from occurring, and referral for dental services when disease is present.

Increase in Cariogenic Bacteria after Initial Periodontal Therapy

This study examined the hypothesis of an intra-oral shift, during initial periodontal therapy, from a periopathogenic to a cariogenic flora. Seventy-one patients with periodontitis were randomly allocated to one of the following treatment strategies: (1) scaling and root planing, quadrant by quadrant, at two-week intervals (NC); (2) full-mouth scaling and root planing within 24 hrs (FRP); or (3) full-mouth disinfection within 24 hrs, including antiseptics [chlorhexidine (CHX) or amine fluoride/stannous fluoride (F) for 2 mos, or CHX for 2 mos followed by F for 6 mos (CHX+F)]. At baseline and after 2, 4, and 8 mos, bacterial samples were taken from supra- and subgingival plaque, saliva, and tongue. The detection frequencies and relative proportions of Streptococcus mutans increased in the NC and FRP groups, but decreased in the F group. In the CHX group, these species disappeared temporarily, but they disappeared for the entire 8 mos in the CHX+F group. These observations were similar for all sample locations. The periopathogens decreased in all groups. This finding confirms the abovementioned hypothesis and indicates a need for caries prophylactic regimens.

Virulence properties of Streptococcus mutans.

Streptococcus mutans is considered one of the primary causative agents of dental caries and can also be a source of infective endocarditis. The main virulence factors associated with cariogenicity include adhesion, acidogenicity, and acid tolerance. Each of these properties works coordinately to alter dental plaque ecology. The ecological changes are characterized by increased proportions of S. mutans and other species that are similarly acidogenic and aciduric. The selection for a cariogenic flora increases the magnitude of the drop in pH following the fermentation of available carbohydrate and increases the probability of enamel demineralization. This review focuses on the bacterial components that contribute to each of the major virulence properties. Further understanding of how these components work together in the development of dental caries will be aided by the recent completion of the sequence of the S. mutans genome and experimental designs that model the dental plaque biofilm.