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

Comparison of biofilm models for producing artificial active white spot lesions

OBJECTIVE

This study compared three protocols for developing artificial white spot lesions (WSL) using biofilm models.

METHODOLOGY

In total, 45 human enamel specimens were sterilized and allocated into three groups based on the biofilm model: Streptococcus sobrinus and Lactobacillus casei (Ss+Lc), Streptococcus sobrinus (Ss), or Streptococcus mutans (Sm). Specimens were incubated in filter-sterilized human saliva to form the acquired pellicle and then subjected to the biofilm challenge consisting of three days of incubation with bacteria (for demineralization) and one day of remineralization, which was performed once for Ss+Lc (four days total), four times for Ss (16 days total), and three times for Sm (12 days total). After WSL creation, the lesion fluorescence, depth, and chemical composition were assessed using Quantitative Light-induced Fluorescence (QLF), Polarized Light Microscopy (PLM), and Raman Spectroscopy, respectively. Statistical analysis consisted of two-way ANOVA followed by Tukey's post hoc test (α=0.05). WSL created using the Ss+Lc protocol presented statistically significant higher fluorescence loss (ΔF) and integrated fluorescence (ΔQ) in comparison to the other two protocols (p<0.001).

RESULTS

In addition, Ss+Lc resulted in significantly deeper WSL (137.5 µm), followed by Ss (84.1 µm) and Sm (54.9 µm) (p<0.001). While high mineral content was observed in sound enamel surrounding the WSL, lesions created with the Ss+Lc protocol showed the highest demineralization level and changes in the mineral content among the three protocols.

CONCLUSION

The biofilm model using S. sobrinus and L. casei for four days was the most appropriate and simplified protocol for developing artificial active WSL with lower fluorescence, higher demineralization, and greater depth.

Bioactive Restorative Materials Applied over Coronal Dentine-A Bibliometric and Critical Review

The objective of the research was to examine the scientific literature concerning restorative materials with bioactive properties for the purpose of covering dentin. Searches were performed in various databases including MEDLINE, Scopus, Web of Science, Cochrane Library, Lilacs/BBO, and Embase. Inclusion criteria involved studies that utilized the terms "dentin" and "bioactive", along with "ion-releasing", "smart materials", "biomimetic materials" and "smart replacement for dentin". The information extracted included the title, authors, publication year, journal and the country of affiliation of the corresponding author. The studies were categorized based on their study design, type of material, substrate, analytical method, and bioactivity. A total of 7161 records were recovered and 159 were included for data extraction. Most of the publications were in vitro studies (n = 149), testing different types of materials in sound dentine (n = 115). Most studies were published in Dental Materials (n = 29), and an increase in publications could be observed after the year 2000. Most of the articles were from the USA (n = 34), followed by Brazil (n = 28). Interfacial analysis was the most investigated (n = 105), followed by bond strength (n = 86). Bioactivity potential was demonstrated for most tested materials (n = 148). This review presents insights into the current trends of bioactive materials development, clearly showing a severe lack of clinical studies.

Effect of anaerobic or/and microaerophilic atmosphere on microcosm biofilm formation and tooth demineralization

OBJECTIVE

Microcosm biofilms can reproduce the complexity of a dental biofilm. However, different forms of cultivation have been used. The impact of the culture atmosphere on the development of microcosm biofilms and their potential to cause tooth demineralization has not yet been deeply studied. This study analyzes the effects of three experimental cultivation models (microaerophile vs. anaerobiosis vs. experimental mixed) on the colony-forming units (CFU) of the cariogenic microorganisms and tooth demineralization.

METHODOLOGY

90 bovine enamel and 90 dentin specimens were distributed into different atmospheres: 1) microaerophilia (5 days, 5% CO2); 2) anaerobiosis (5 days, jar); 3) mixed (2 days microaerophilia and 3 days anaerobiosis), which were treated with 0.12% chlorhexidine (positive control - CHX) or Phosphate-Buffered Saline (negative control - PBS) (n=15). Human saliva and McBain's saliva containing 0.2% sucrose were used for microcosm biofilm formation, for 5 days. From the second day to the end of the experiment, the specimens were treated with CHX or PBS (1x1 min/day). Colony-forming units (CFU) were counted, and tooth demineralization was analyzed using transverse microradiography (TMR). Data were subjected to two-way ANOVA and Tukey's or Sidak's test (p<0.05).

RESULTS

CHX was able to reduce total microorganism's CFU compared to PBS (differences of 0.3-1.48 log10 CFU/mL), except for anaerobiosis and microaerophilia in enamel and dentin biofilm, respectively. In the case of dentin, no effect of CHX on Lactobacillus spp. was observed. CHX significantly reduced enamel demineralization compared to PBS (78% and 22% reductions for enamel and dentin, respectively). Enamel mineral loss did not differ when compared with the other atmospheres; however, the enamel lesion depth was greater under anaerobiosis. Dentin mineral loss was lower under anaerobiosis when compared with the other atmospheres.

CONCLUSION

The type of atmosphere has, in general, little influence on the cariogenic ability of the microcosm biofilm.

A 3D-Printed Customizable Platform for Multiplex Dynamic Biofilm Studies

Biofilms are communities of microbes that colonize surfaces. While several biofilm experimental models exist, they often have limited replications of spatiotemporal dynamics surrounding biofilms. For a better understanding dynamic and complex biofilm development, this manuscript presents a customizable platform compatible with off-the-shelf well plates that can monitor microbial adhesion, growth, and associated parameters under various relevant scenarios by taking advantage of 3D printing. The system i) holds any substrate in a stable, vertical position, ii) subjects samples to flow at different angles, iii) switches between static and dynamic modes during an experiment, and iv) allows multiplexing and real-time monitoring of biofilm parameters. Simulated fluid dynamics is employed to estimate flow patterns around discs and shear stresses at disc surfaces. A 3D printed peristaltic pump and a customized pH measurement system for real-time tracking of spent biofilm culture media are equipped with a graphical user interface that grants control over all experimental parameters. The system is tested under static and dynamic conditions with Streptococcus mutans using different carbon sources. By monitoring the effluent pH and characterizing biochemical, microbiological, and morphological properties of cultured biofilms, distinct properties are demonstrated. This novel platform liberates designing experimental strategies for investigations of biofilms under various conditions.

Characterization of white spot lesions formed on human enamel under microcosm biofilm for different experimental periods

The initial characteristics of white spot lesion (WSLs), such as the degree of integrated mineral loss (ΔZ), depth and pattern of mineral distribution, have an impact on further demineralization and remineralization. However, these lesion parameters have not been evaluated in WSLs produced from microcosm biofilms.

Mucoadhesive controlled-release formulations containing morin for the control of oral biofilms

This study aimed to evaluate the antimicrobial and anti-biofilm activity of morin on polymicrobial biofilms and its cytotoxicity in controlled-release films and tablets based on gellan gum. Polymicrobial biofilms were formed from saliva for 48 h under an intermittent exposure regime to 1% sucrose and in contact with films or tablets of gellan gum containing 2 mg of morin each. Acidogenicity, bacterial viability, dry weight and insoluble extracellular polysaccharides from biofilms were evaluated. The cytotoxicity of morin was evaluated in oral keratinocytes. Morin released from the systems reduced the viability of all the microbial groups evaluated, as well as the dry weight and insoluble polysaccharide concentration in the matrix and promoted the control of acidogenicity when compared with the control group without the substance. Morin was cytotoxic only at the highest concentration evaluated. In conclusion, morin is an effective agent and shows antimicrobial and anti-biofilm activity against polymicrobial biofilms.

Effect of ionizing radiation and cariogenic biofilm challenge on root-dentin caries

OBJECTIVES

To evaluate the effect of ionizing radiation and cariogenic biofilm challenge using two continuous flow models, normal and reduced salivary flow, on the development of initial root-dentin caries lesions.

MATERIALS AND METHODS

Microcosm biofilms were grown under two salivary flow rates (0.06 and 0.03 mL min^-1) and exposed to 5% sucrose (3 × daily, 0.25 mL min^-1, 6 min) dripped over non-irradiated and irradiated root-dentin blocks for up to 7 days. The vibration modes of root dentin, matrix/mineral (M/M), and carbonate/mineral (C/M) ratios were evaluated by FTIR. The mineral density was assessed by micro-CT.

RESULTS

With normal salivary flow, FTIR revealed an increase in the organic matrix (amide III) and a decrease in the mineral phase (ν_4, ν₂ PO₄^3-, AII + ν₂ CO₃^2-, C/M) in caries lesions. Irradiated dentin exhibited a reduction in the mineral phase (ν₁, ν₃ PO₄^3-, ν₂ CO₃^2-, C/M). Differences in mineral densities were not significant. With reduced salivary flow, FTIR also revealed increased organic matrix (amide III) for irradiated caries lesions and decrease in mineral phase (v_4, v₂ PO₄^3-, v₂ CO₃^2-, and C/M) in caries lesions. ν₁, ν₃ PO₄^3- precipitated on the surface of irradiated dentin and a lower mineral density was observed.

CONCLUSIONS

Initial caries lesions differed between non-irradiated and irradiated dentin and between normal and reduced salivary flow rates. Significant mineral loss with exposure of the organic matrix and low mineral density were observed for irradiated dentin with a reduced salivary flow rate.

CLINICAL RELEVANCE

Ionizing radiation associated with a reduced salivary flow rate enhanced the progression of root-dentin caries.

Influence of biofilm removal from the tooth-restoration interface on the progression of secondary caries lesions: a preliminary in vitro model study

This study investigated the effects of biofilm removal from the tooth-restoration surface on secondary caries lesion progression. Biofilms were grown for up to 28 days on resin-restored enamel-dentin disks with an interfacial gap with DMM or DMM + 1% sucrose under five different protocols of Visible Biofilm Removal (V-BR; n = 7): (1) without V-BR, (2) with partial V-BR, (3) with total V-BR, (4) with total V-BR and saliva reinoculation, and (5) without V-BR under 9 h of cariogenic challenge. V-BR was performed at 7, 14 and 21 days. ΔS and CFU counts served as outcome variables. Linear regression models showed that ΔS values were higher for outer lesions than wall lesions, and outer lesion progression generally increased over time (p < 0.01). All protocols tested, except total V-BR, increased the lactobacilli count (p < 0.005). V-BR did not influence the progression of caries lesions on the cavity wall in this biofilm model.

Mini-review: from in vitro to ex vivo studies: an overview of alternative methods for the study of medical biofilms

Microbial biofilms are a natural adaptation of microorganisms, typically composed of multiple microbial species, exhibiting complex community organization and cooperation. Biofilm dynamics and their complex architecture are challenging for basic analyses, including the number of viable cells, biomass accumulation, biofilm morphology, among others. The methods used to study biofilms range from in vitro techniques to complex in vivo models. However, animal welfare has become a major concern, not only in society, but also in the academic and scientific field. Thus, the pursuit for alternatives to in vivo biofilm analyses presenting characteristics that mimic in vivo conditions has become essential. In this context, the present review proposes to provide an overview of strategies to study biofilms of medical interest, with emphasis on alternatives that approximate experimental conditions to host-associated environments, such as the use of medical devices as substrata for biofilm formation, microcosm and ex vivo models.

Characterization of polymicrobial biofilms obtained from saliva or carious lesions in dentin

This study aimed to compare the formation of polymicrobial biofilms using carious dentin or saliva as inoculum for application in in vitro microbiological studies on caries research. For biofilm growth, combined samples of infected dentin or saliva from three donors were used. The biofilms were grown on glass coverslips, under a regimen of intermittent exposure (6 h day^-1) to 1% sucrose for 4 days. Total bacterial loads, as well as specific aciduric bacteria and mutans streptococci loads were quantified and correlated with biofilm acidogenicity and susceptibility to chlorhexidine. The data were evaluated using the Student's-t, Mann Whitney and Kruskal-Wallis tests. The two biofilms showed similar microbial loads (total bacteria, aciduric bacteria and mutans streptococci) on day 4, and high acidogenicity after 48 h and were susceptible to chlorhexidine at different time intervals. In conclusion, both dentin and saliva can be used as an inoculum in in vitro studies of processes related to biofilm formation.

Effect of arginine on microorganisms involved in dental caries: a systematic literature review of in vitro studies

This systematic review aimed to discuss the effects of arginine on caries-related microorganisms in different in vitro biofilm models. The eligibility criteria were in vitro studies that evaluated the effect of arginine at different concentrations on caries-related microorganisms using biofilm models. Eighteen studies published between 2012 and 2019 were included. Different bacterial species were studied. Seventeen studies (94.4%) achieved a low risk of bias and only one showed a medium risk of bias. The studies showed that arginine is a promising approach for the ecological management of dental caries. The focus of this review was to evaluate the effects of arginine on microorganisms involved in the mechanism of dental caries.

The Effect of a Charcoal-based Powder for Enamel Dental Bleaching

Clinical Relevance

Charcoal based-powders are not effective for dental bleaching.

SUMMARY

Charcoal-based dentifrices for dental whitening are a novelty in the market. Manufacturers claim that such charcoal-based products have whitening, remineralization, antimicrobial, and antifungal properties of charcoal in such products. However, there is no substantial scientific evidence for these claims. This laboratory randomized study was designed to evaluate the whitening properties of a charcoal-based toothpowder. A total of 45 bovine dental enamel discs were randomly distributed into three groups (n=15): group 1, mechanical brushing with a 1450-ppm F toothpaste (control group); group 2, mechanical brushing with an activated charcoal-based powder; group 3, bleaching per the standard protocol using 10% carbamide peroxide. The surface roughness and color of each specimen were analyzed at baseline and after 14 days of experiment. The surface of one randomly selected specimen from each group was examined using a scanning electron microscope (SEM). The Kruskal-Wallis test was used to compare groups at a significance level of 5%. Only group 3 promoted a statistically significant effect on ΔE compared with groups 1 and 2 (p&lt;0.001 and p=0.003, respectively). No statistically significant difference was found between groups for surface roughness (p&gt;0.05). SEM revealed a more irregular surface in group 1 specimens compared with group 2 and 3 specimens. The charcoal-based powder did not seem to have any bleaching effect.

Effect of commercial herbal toothpastes and mouth rinses on the prevention of enamel demineralization using a microcosm biofilm model

This work evaluated the effects of commercial toothpastes and mouth rinses containing natural/herbal agents on biofilm viability, extracellular polysaccharide (EPS) production and on enamel demineralization in vitro. Microcosm biofilm was produced on bovine enamel for 5 days and treated daily with: Orgânico natural^® (toothpaste/mouth rinse), Boni Natural Menta & Malaleuca^® (toothpaste/mouth rinse), Propolis & Myrrh^® (toothpaste), Colgate Total 12 Clean Mint^® (toothpaste, positive control), Malvatricin^® Plus (mouth rinse), PerioGard^® (mouth rinse, positive control) or PBS (negative control). Tom's Propolis & Myrrh^® and Colgate Total 12^® toothpastes and Malvatricin^® Plus and PerioGard^® mouth rinses significantly reduced biofilm viability (p < 0.05). Only PerioGard^® had significant effects on biofilm thickness and EPS. Despite the indication that Tom's Propolis & Myrrh^® significantly reduced lesion depth, only Colgate Total 12^® significantly reduced mineral loss. Malvatricin^® Plus significantly reduced mineral loss and lesion depth, as did PerioGard^®. Some herbal products, Malvatricin^® Plus and Tom's Propolis & Myrrh^®, showed anticaries effects.

Impact of a diagnostic workshop on undergraduate teaching-learning process for the diagnosis and management of tooth restorations-A randomised controlled study

OBJECTIVE

The aim of this study was to investigate the impact of a diagnostic workshop on undergraduate teaching-learning process for the diagnosis and management of tooth restorations.

METHODS

The first stage of the study was a randomised controlled study with two parallel groups: lecture (L) and lecture coupled with a diagnostic workshop (LW). A pool of cases of tooth restorations including secondary caries and marginal defects was used for training. Theoretical knowledge, perception about the activity and practical abilities were evaluated. The second stage of the study assessed students' theoretical knowledge retention six months following intervention. All students included in the first stage of the study were exposed to LW. Hence, a new control group of students not exposed to LW was selected. One-way analysis of variance, Fisher's exact test, Kruskal-Wallis test and multilevel regression analysis were used as part of statistical analysis.

RESULTS

The LW group had greater scores for the assignment of lesion severity and activity, presence of marginal defect and treatment indication than the L group (P < 0.05). Multilevel regression analysis showed a positive impact of the workshop diagnosis in the correct assessment of lesion activity (P = 0.03). There was no statistical difference between the LW and L groups in students' perception of the activity. The LW group showed greater knowledge retention after six months than the L group (P = 0.027).

CONCLUSION

Lecture coupled with diagnostic workshop improved students' practical skills of diagnosis restorations and knowledge retention in the six months following intervention.

Effect of hydroalcoholic extract of Myracrodruon urundeuva All. and Qualea grandiflora Mart. leaves on the viability and activity of microcosm biofilm and on enamel demineralization

OBJECTIVES

The aim of this study was to assess the effect of Myracrodruon urundeuva All. and Qualea grandiflora Mart. leaves hydroalcoholic extracts on viability and metabolism of a microcosm biofilm and on enamel demineralization prevention.

METHODOLOGY

Microcosm biofilm was produced on bovine enamel using inoculum from pooled human saliva mixed with McBain saliva, under 0.2% sucrose exposure, for 14 days. The biofilm was daily-treated with the extracts for 1 min. At the end, it was analyzed with respect to viability by fluorescence, CFU counting and extracellular polysaccharides (phenol-sulphuric acid colorimetric assay) and lactic acid (enzymatic assay) production. The demineralization was measured by TMR. The data were compared using ANOVA or Kruskal-Wallis (p<0.05).

RESULTS

M. urundeuva All. at 100, 10 and 0.1 μg/mL and Q. grandiflora Mart. at 100 and 0.1 μg/mL reduced biofilm viability similarly to positive control (chlorhexidine) and significantly more than the negative-vehicle control (35% ethanol). M. urundeuva at 1000, 100 and 0.1 μg/mL were able to reduce both lactobacilli and mutans streptococci CFU counting, while Q. grandiflora (1000 and 1.0 μg/mL) significantly reduced mutans streptococci CFU counting. On the other hand, the natural extracts were unable to significantly reduce extracellular polysaccharides and lactic acid productions neither the development of enamel carious lesions.

CONCLUSIONS

The extracts showed antimicrobial properties on microcosm biofilm, however, they had no effect on biofilm metabolism and caries protection.

Comparison between static and semi-dynamic models for microcosm biofilm formation on dentin

OBJECTIVE

Microcosm biofilm has been applied to induce carious lesions in dentin. However, no study has been done to compare the impact of the type of model for providing nutrients to microcosm biofilm formation on dentin. This study compared the performance of two kinds of models (static and semi-dynamic) on the biofilm formation and the development of dentin carious lesions.

MATERIAL AND METHODS

In both models, biofilm was produced using inoculum from pooled human saliva mixed with McBain saliva for the first 8 h (5% CO2 and 37°C). Afterwards, for the static model, the samples were placed in 24-wells microplate containing McBain saliva with 0.2% sucrose, which was replaced at 24 h. In the semi-dynamic model, the samples were submitted to artificial mouth system with continuous flow of McBain saliva with 0.2% sucrose (0.15 ml/min, 37°C) for 10 h a day (for the other 14 h, no flow was applied, similarly to the static model). After 5 days, biofilm viability was measured by fluorescence and dentin demineralization by transverse microradiography.

RESULTS

Biofilm viability was significantly lower for the static compared with semi-dynamic model, while dentin demineralization was significantly higher for the first one (p<0.05). The static model was able to produce a higher number of typical subsurface lesions compared with the semi-dynamic model (p<0.05).

CONCLUSIONS

The type of model (static and semi-dynamic) applied in the microcosm biofilm may have influence on it's viability and the severity/profile of dentin carious lesions.

The role of human milk and sucrose on cariogenicity of microcosm biofilms

This study investigated the effect of human milk, alone and associated with sucrose, in the cariogenicity of biofilms in a microcosm biofilm model and compared with the cariogenicity of sucrose and bovine milk. Microcosm biofilms were grown in enamel discs in 24-well plates. Six growth conditions were studied: DMM (chemically defined artificial saliva - negative control), DMM with 1% of sucrose (DMM+s) (positive control), human milk with DMM, human milk with DMM+s, bovine milk with DMM, and bovine milk with DMM+s. After 5 days, the outcome variables surface hardness change (%SHC), microbiological composition of biofilms, and pH of supernatant were analyzed. All groups had significantly lower hardness loss compared to the DMM group with 1% of sucrose. Human and bovine milk associated with sucrose showed higher hardness loss. The supernatant pH values after 6 hours of different treatments were similar for the groups sucrose and human milk associated with sucrose (p>0.05). After 18 hours at rest in pure DMM, an increase in the pH of the supernatant was observed. Higher values of total microorganisms count were found for sucrose and bovine milk groups compared to the group supplemented only by DMM. Bovine milk group showed greater amount of total aciduric microorganisms in comparison to human milk group. Within the limits of this study, it can be infered that both human and cow milks have some cariogenic potential, although differing from sucrose in terms of mineral loss.

Strategies for combating bacterial biofilms: A focus on anti-biofilm agents and their mechanisms of action

Biofilm refers to the complex, sessile communities of microbes found either attached to a surface or buried firmly in an extracellular matrix as aggregates. The biofilm matrix surrounding bacteria makes them tolerant to harsh conditions and resistant to antibacterial treatments. Moreover, the biofilms are responsible for causing a broad range of chronic diseases and due to the emergence of antibiotic resistance in bacteria it has really become difficult to treat them with efficacy. Furthermore, the antibiotics available till date are ineffective for treating these biofilm related infections due to their higher values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), which may result in in-vivo toxicity. Hence, it is critically important to design or screen anti-biofilm molecules that can effectively minimize and eradicate biofilm related infections. In the present article, we have highlighted the mechanism of biofilm formation with reference to different models and various methods used for biofilm detection. A major focus has been put on various anti-biofilm molecules discovered or tested till date which may include herbal active compounds, chelating agents, peptide antibiotics, lantibiotics and synthetic chemical compounds along with their structures, mechanism of action and their respective MICs, MBCs, minimum biofilm inhibitory concentrations (MBICs) as well as the half maximal inhibitory concentration (IC₅₀) values available in the literature so far. Different mode of action of anti biofilm molecules addressed here are inhibition via interference in the quorum sensing pathways, adhesion mechanism, disruption of extracellular DNA, protein, lipopolysaccharides, exopolysaccharides and secondary messengers involved in various signaling pathways. From this study, we conclude that the molecules considered here might be used to treat biofilm-associated infections after significant structural modifications, thereby investigating its effective delivery in the host. It should also be ensured that minimum effective concentration of these molecules must be capable of eradicating biofilm infections with maximum potency without posing any adverse side effects on the host.

Effect of a mouthrinse containing Malva sylvestris on the viability and activity of microcosm biofilm and on enamel demineralization compared to known antimicrobials mouthrinses

The purpose of this study was to evaluate the antimicrobial (anti-biofilm) and anti-caries (enamel demineralization prevention) effects of Malva sylvestris (Malvatricin^® Plus) compared with known antimicrobial mouthrinses. Microcosm biofilm was produced on enamel, using inoculum from pooled human saliva mixed with McBain saliva (0.2% sucrose) for 14 days. The biofilm was treated with mouthrinses for 1 min day^-1. Oral-B^® Complete, Listerine^® Zero and Malvatricin^® Plus had the greatest effect on the reduction of biofilm viability (p < 0.0001). On the other hand, lactic acid production was reduced significantly with PerioGard^®, Noplak^® Max and Listerine^® Zero compared with the control (p < 0.0001). No significant differences were found among the mouthrinses with respect to the colony-forming unit counting (total microorganisms, total streptococci, mutans streptococci and lactobacilli) and extracellular polysaccharide production. Enamel demineralization was reduced significantly with PerioGard^®, Noplak^® Max and Malvatricin^® Plus compared with the control (p < 0.0001). Malva sylvestris has a comparable anti-caries effect to chlorhexidine mouthrinses.

Analysis of the antimicrobial and anti-caries effects of TiF4 varnish under microcosm biofilm formed on enamel

Titanium tetrafluoride (TiF4) is known for interacting with enamel reducing demineralization. However, no information is available about its potential antimicrobial effect.

OBJECTIVES

This study evaluated the antimicrobial and anti-caries potential of TiF4 varnish compared to NaF varnish, chlorhexidine gel (positive control), placebo varnish and untreated (negative controls) using a dental microcosm biofilm model.

MATERIAL AND METHODS

A microcosm biofilm was produced on bovine enamel previously treated with the varnishes, using inoculum from human saliva mixed with McBain saliva, under 0.2% sucrose exposure, for 14 days. All experiments were performed in biological triplicate (n=4/group in each experiment). Factors evaluated were: bacterial viability (% dead and live bacteria); CFU counting (log10 CFU/mL); and enamel demineralization (transverse microradiography - TMR). Data were analysed using ANOVA/Tukey's test or Kruskal-Wallis/Dunn's test (p<0.05).

RESULTS

Only chlorhexidine significantly increased the number of dead bacteria (68.8±13.1% dead bacteria) compared to untreated control (48.9±16.1% dead bacteria). No treatment reduced the CFU counting (total microorganism and total streptococci) compared to the negative controls. Only TiF4 was able to reduce enamel demineralization (ΔZ 1110.7±803.2 vol% μm) compared to both negative controls (untreated: ΔZ 4455.3±1176.4 vol% μm).

CONCLUSIONS

TiF4 varnish has no relevant antimicrobial effect. Nevertheless, TiF4 varnish was effective in reducing enamel demineralization under this model.

Red fluorescence of dental biofilm as an indicator for assessing the efficacy of antimicrobials

The study aimed to determine whether the red fluorescence (RF) of a dental microcosm biofilm as measured with quantitative light-induced fluorescence (QLF) technology is useful for assessing the efficacy of antimicrobials. Dental microcosm biofilms were formed on bovine enamel discs and grown under 0.3% sucrose challenge and treated with chlorhexidine (CHX) solutions at different concentrations (0.05%, 0.1%, and 0.5%) plus a negative control [sterile distilled water (DW)] twice daily for 7 days. The biofilms were photographed using a QLF-digital system to evaluate the RF by calculating the red/green ratio, and pH values of the medium were measured daily. After 7 days, the bacterial viability of the biofilm was assessed by measuring the counts of viable total bacteria and aciduric bacteria, and the percentage surface microhardness changes (%SHC) was evaluated. The RF and cariogenic properties were compared for the different concentrations of CHX, and their correlations were examined. The RF and its increase rate were much lower for CHX-treated biofilms than for DW-treated biofilms. The RF after 7 days of maturation decreased significantly with increasing CHX concentrations (p<0.001) and was from 31% (for 0.05% CHX) to 46% (for 0.5% CHX) lower than that of the DW group. Strong correlations were reported between the RF of the 7-day-maturation biofilms and cariogenic properties, such as the number of total bacteria (r=0.93), number of aciduric bacteria (r=0.97), supernatant pH (r=0.43), and %SHC (r=0.98). In conclusion, the RF of dental biofilms as measured with QLF technology can be used to nondestructively assess and monitor the effect of antimicrobials against biofilm.

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.