Corrosion behaviour of titanium in the presence of Streptococcus mutans

Objective

The main aim of this in vitro study was to evaluate the influence of Streptococcus mutans on the corrosion of titanium.

Methods

S. mutans biofilms were formed on commercially pure titanium (CP-Ti) square samples (10 mm × 10 mm × 1 mm) using a culture medium enriched with sucrose. Open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion behaviour of CP-Ti in the presence of S. mutans in Fusayama's artificial saliva. The corrosion of biofilm-free CP-Ti samples was also evaluated in artificial saliva. Biofilms biomass was measured by spectrophotometry, using crystal violet staining, after 1, 2 and 7 days.

Results

The OCP values recorded on CP-Ti in the presence of S. mutans (−0.3 ± 0.02 V vs. SCE) was lower than those on biofilm-free CP-Ti (−0.1 ± 0.01 V vs. SCE) after 2 h of immersion in artificial saliva (p < 0.05). That reveals a high reactivity of titanium in presence of S. mutans. Impedance spectra revealed the formation of a compact passive film on titanium in artificial saliva or in the presence of a 2 days old S. mutans biofilm even though the corrosion resistance of CP-Ti has decreased in presence of a S. mutans biofilm.

Conclusion

The presence of bacterial colonies, such as S. mutans, negatively affected the corrosion resistance of the titanium.     

Evaluation of Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity

Objectives

The aim of this study was to evaluate Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity.

Methods

After producing fluoride varnish-coated hydroxyapatite discs using Fluor Protector (FP), Bifluorid 12 (BIF), Cavity Shield (CASH), or Flor-Opal Varnish White (FO), S. mutans biofilms were formed on the discs. To assess S. mutans adhesion to the discs, 4-h-old biofilms were analysed. To investigate the change in biofilm accumulation during subsequent biofilm formation, the biomass, colony forming units (CFU), and water-insoluble extracellular polysaccharides (EP) of 46-, 70-, and 94-h-old biofilms were analysed. To investigate the change in acidogenicity, pH values of the culture medium were determined during the experimental period. The amount of fluoride in the culture medium was also determined during the experimental period.

Results

BIF, CASH, and FO affected S. mutans adhesion (67–98% reduction) and subsequent biofilm accumulation in 46-, 70-, and 94-h-old biofilms. However, the reducing effect of the fluoride varnishes on the biomass, CFU count, water-insoluble EP amount, and acid production rate of the biofilms decreased as the biofilm age increased. These results may be related to the fluoride-release pattern of the fluoride varnishes. Of the fluoride varnishes tested, FO showed the highest reducing effect against the bacterial adhesion and subsequent biofilm accumulation.

Conclusions

Our findings suggest that if the results of these experiments are extrapolable to the in vivo situation, then reduced clinical benefit of using fluoride varnishes may occur with time.

Clinical significance

Fluoride varnish application can affect cariogenic biofilm formation but the anti-biofilm activity may be reduced with time.     

Effects of xylitol mouthrinse on Streptococcus mutans

Objectives

This study aimed to measure the effect of xylitol mouthrinse on salivary Streptococcus mutans counts.

Methods

Subjects in the study group (n = 25) used xylitol mouthrinse for 4 weeks, while another group (n = 25) used saccharine mouthrinse. S. mutans were measured before and after intervention.

Results

At the baseline the mean S. mutans scores were 3.9 (SE = 0.03) and 3.9 (0.04) for the xylitol group and control group respectively, while the scores were 2.8 (0.13) and 3.9 (0.07) after the intervention. Significant reductions (p < 0.01) in the scores of S. mutans were found after the four week use of xylitol mouthrinse.

Conclusions

Significant reductions in the scores of S. mutans were found after the four week use of 20% xylitol mouthrinse. The bacteriostatic effect of xylitol mouthrinse on S. mutans may be comparable to other xylitol products. Further studies are needed to confirm both the short and long term effects of xylitol mouthrinse.     

Effect of desensitising paste containing 8% arginine and calcium carbonate on biofilm formation of Streptococcus mutans in vitro

Objectives

To evaluate the influence of desensitising paste containing 8% arginine and calcium carbonate (Ar-Ca) on biofilm formation on dentine.

Methods

Dentine discs were cut from extracted third molars and divided into the following three groups: no treatment, pumice treatment and Ar-Ca treatment. Surface topography and roughness were examined using scanning electron microscopy (SEM) and non-contact 3D surface profiler. After sterilisation, samples were incubated with Streptococcus mutans (S. mutans) for 4 h, 24 h and 72 h. Bacterial adhesion and biofilm formation were analysed using SEM, whereas MTT and lactic acid production assays were used to analyse the metabolic activity of S. mutans.

Results

After polishing with either pumice or Ar-Ca, the surfaces of the samples became smoother than in the control group. The Ra values of the three experimental groups decreased significantly to 0.43 μm, 0.3 μm and 0.26 μm, respectively. Compared to the control group, fewer bacteria adhered to the dentine surface in the Ar-Ca group, while biofilm thickness decreased significantly for both groups after incubating for 24 h and 72 h. MTT and lactic acid production levers also showed a significant reduction in the Ar-Ca group.

Conclusions

Ar-Ca appears to present antibiofilm efficacy and may provide a promising approach to combat bacterial infection in hypersensitive dentinal lesions.

Clinical significance

As a clinical application of desensitising polishing paste, the paste containing 8% arginine and calcium carbonate could also inhibit the biofilm formation effectively.     

An in vitro study of alginate oligomer therapies on oral biofilms

Objectives

The in vitro effect of a novel, oligosaccharide nanomedicine OligoG against oral pathogen-related biofilms, both alone and in the presence of the conventional anti-bacterial agent triclosan, was evaluated.

Methods

The effect of OligoG ± triclosan was assessed against established Streptococcus mutans and Porphyromonas gingivalis biofilms by bacterial counts and image analysis using LIVE/DEAD^® staining and atomic force microscopy (AFM). The effect of triclosan and OligoG surface pre-treatments on bacterial attachment to titanium and polymethylmethacrylate was also studied.

Results

OligoG potentiated the antimicrobial effect of triclosan, particularly when used in combination at 0.3% against S. mutans grown in artificial saliva. OligoG was less effective against established P. gingivalis biofilms. However, attachment of P. gingivalis, to titanium in particular, was significantly reduced after surface pre-treatment with OligoG and triclosan at 0.01% when compared to controls. Light microscopy and AFM showed that OligoG was biocidal to P. gingivalis, but not S. mutans.

Conclusions

OligoG and triclosan when used in combination produced an enhanced antimicrobial effect against two important oral pathogens and reduced bacterial attachment to dental materials such as titanium, even at reduced triclosan concentrations. Whilst the use of triclosan against oral bacteria has been widely documented, its synergistic use with OligoG described here, has not previously been reported. The use of lower concentrations of triclosan, if used in combination therapy with OligoG, could have environmental benefits.

Clinical importance

The potentiation of antimicrobial agents by naturally occurring oligomers such as OligoG may represent a novel, safe adjunct to conventional oral hygiene and periodontal therapy. The ability of OligoG to inhibit the growth and impair bacterial adherence highlights its potential in the management of peri-implantitis.     

Sensitivity of Candida albicans biofilm cells grown on denture acrylic to antifungal proteins and chlorhexidine

Objectives

Candida albicans cells form biofilms on polymeric surfaces of dentures and other prostheses introduced into the oral cavity. Many biofilm microorganisms exhibit resistance to antimicrobial agents; C. albicans cells may also develop resistance to naturally occurring antifungal peptides in human saliva including histatins (Hsts) and defensins (hBDs). Therefore, we evaluated Hst 5 activity on C. albicans biofilm cells compared to planktonic cells and measured whether surface treatment of denture acrylic with Hst 5, hBD-3, or chlorhexidine gluconate could inhibit in vitro biofilm development.

Methods

Acrylic disks were preconditioned with 500 μl saliva for 30 min, and inoculated with C. albicans cells (10⁶ cells/ml) for 1 h, at 37 °C. Non-adherent cells were removed by washing and disks and were incubated in YPD growth medium for 24, 48, and 72 h at 37 °C. Candidacidal assays were performed on 48-h-biofilms and on planktonically grown cells using Hst 5 (15.5, 31.25, and 62 μM). Cell adhesion was compared on disks pre-coated with 0.12% chlorhexidine gluconate, 50 μM Hst 5, or 0.6 μM hBD-3 after 24, 48, and 72 h growth.

Results

No significant difference was observed in sensitivity to Hst 5 of biofilm cells compared to planktonic cells (p > 0.05). Pre-coating disks with hBD-3 did not inhibit biofilm development; however, Hst 5 significantly inhibited biofilm development at 72 h, while 0.12% chlorhexidine significantly inhibited biofilm development at all time intervals (p < 0.05).

Conclusions

C. albicans biofilm cells grown on denture acrylic are sensitive to killing by Hst 5. Surface coating acrylic with chlorhexidine or Hst 5 effectively inhibits biofilm growth and has potential therapeutic application.     

Hydrophilicity of dentin bonding systems influences in vitro Streptococcus mutans biofilm formation

Objective

To evaluate in vitro Streptococcus mutans (S. mutans) biofilm formation on the surface of five light-curing experimental dental bonding systems (DBS) with increasing hydrophilicity. The null hypothesis tested was that resin chemical composition and hydrophilicity does not affect S. mutans biofilm formation.

Methods

Five light-curing versions of experimental resin blends with increasing hydrophilicity were investigated (R₁, R₂, R₃, R₄ and R₅). R₁ and R₂ contained ethoxylated BisGMA/TEGDMA or BisGMA/TEGDMA, respectively, and were very hydrophobic, were representative of pit-and-fissure bonding agents. R₃ was representative of a typical two-step etch-and-rinse adhesive, while R₄ and R₅ were very hydrophilic resins analogous to self-etching adhesives. Twenty-eight disks were prepared for each resin blend. After a 24 h-incubation at 37 °C, a multilayer monospecific biofilm of S. mutans was obtained on the surface of each disk. The adherent biomass was determined using the MTT assay and evaluated morphologically with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM).

Results

R₂ and R₃ surfaces showed the highest biofilm formation while R₁ and R₄ showed a similar intermediate biofilm formation. R₅ was more hydrophilic and acidic and was significantly less colonized than all the other resins. A significant quadratic relationship between biofilm formation and hydrophilicity of the resin blends was found. CLSM and SEM evaluation confirmed MTT assay results.

Conclusions

The null hypothesis was rejected since S. mutans biofilm formation was influenced by hydrophilicity, surface acidity and chemical composition of the experimental resins. Further studies using a bioreactor are needed to confirm the results and clarify the role of the single factors.     

Probiotic Lactobacillus reuteri strains ATCC PTA 5289 and ATCC 55730 differ in their cariogenic properties in vitro

Objective

The effects of probiotics on cariogenic biofilms remain controversial. Our aim was to characterise two probiotic Lactobacillus reuteri strains, ATCC PTA 5289 and ATCC 55730 from a cariogenic standpoint in vitro. These strains are used in commercial products designed for oral health purposes.

Design

The adhesion and biofilm formation were studied on saliva-coated hydroxyapatite. The effects of glucose or sucrose on the biofilm formation were also tested. Arginine metabolism was assessed by measuring the pH in the presence of glucose and arginine. The degradation of hydroxyapatite was measured in three different growth media. Streptococcus mutans strains Ingbritt and MT 8148 were used as positive controls for bacterial adhesion and degradation of hydroxyapatite.

Results

Strain ATCC PTA 5289 adhered on saliva-coated hydroxyapatite and formed detectable biofilm, but strain ATCC 55730 was poor in both adhesion and biofilm formation. Both strains were arginolytic and raised the pH in the presence of arginine. The amount of dissolved calcium from hydroxyapatite correlated with bacterial growth rate and the final pH of the growth medium.

Conclusion

L. reuteri strains ATCC PTA 5289 and ATCC 55730 differed in their adhesion, biofilm formation and arginine metabolism in vitro. Thus, these probiotic lactobacilli are likely to differ in their behaviour and cariogenic potential also in an oral environment.     

Inhibition of microbial adhesion to plastic surface and human buccal epithelial cells by Rhodomyrtus tomentosa leaf extract

Objective

The adherence of oral pathogenic microorganisms to host tissues is the initial step for successful process of oral diseases. This study aimed to determine the effect of the Rhodomyrtus tomentosa leaf extract and rhodomyrtone, an antibacterial compound from R. tomentosa leaf, on adhesion of some oral pathogens to polystyrene plastic surface and human buccal epithelial cells.

Methods

The minimum inhibitory concentration (MIC) was evaluated using broth microdilution method. The microbial adhesion to the plastic surface and buccal cells was determined using microtiter plate method and microscopy technique.

Results

The ethanol extract of leaf demonstrated antibacterial activity against oral microorganisms including Staphylococcus aureus ATCC 25923, Streptococcus mutans (clinical isolate), and Candida albicans ATCC 90028 with the MIC values of 31.25, 15.62, and 1000 μg/ml, respectively. Rhodomyrtone displayed activity with the MIC values of 0.78 and 0.39 μg/ml against S. aureus ATCC 25923 and S. mutans, respectively. The MIC value of the compound against C. albicans ATCC 90028 was more than 100 μg/ml which was the highest test concentration. All pathogenic microorganisms treated with the extract and rhodomyrtone at their subinhibitory concentrations resulted in a decrease in their adherence ability to both plastic surface and buccal cells.

Conclusion

It is suggested that R. tomentosa extract and rhodomyrtone may be useful in therapy or as prophylaxis in infections involving oral pathogens.     

Correlation of Streptococcus mutans and Streptococcus sanguinis colonization and ex vivo hydrogen peroxide production in carious lesion-free and high caries adults

Objective

This study was conducted to estimate oral colonization by Streptococcus mutans and Streptococcus sanguinis in adults with high and without any caries experience. Furthermore, differences in the amount of hydrogen peroxide (H₂O₂) produced by S. sanguinis isolated from both groups were assessed.

Design

Forty adults were divided into: (i) carious lesion-free, without any carious lesion, assessed by the International Caries Detection and Assessment System (ICDAS), or restoration, (CF) and (ii) high caries experience (HC). Saliva samples were collected and seeded on respective agar-plates for enumeration of total streptococci, S. mutans and S. sanguinis (CFU/mL) and compared between groups. Additionally, S. sanguinis colonies obtained from both groups were inoculated on Prussian blue agar for H₂O₂ detection. Production of H₂O₂ was quantified and compared between the two groups. S. sanguinis counts were significantly higher in CF than HC individuals (p < 0.05). Conversely, S. mutans showed significantly higher levels in HC than CF subjects (p < 0.001). S. sanguinis colonies from CF individuals produced significantly larger H₂O₂ halos compared with HC subjects.

Conclusions

S. sanguinis predominates over S. mutans in saliva of adults without caries experience. In those people, S. sanguinis produces more H₂O₂ex vivo.     

Application of an active attachment model as a high-throughput demineralization biofilm model

Objectives

To investigate the potential of an active attachment biofilm model as a high-throughput demineralization biofilm model for the evaluation of caries-preventive agents.

Methods

Streptococcus mutans UA159 biofilms were grown on bovine dentine discs in a high-throughput active attachment model. Biofilms were first formed in a medium with high buffer capacity for 24 h and then subjected to various photodynamic therapies (PACT) using the combination of Light Emitting Diodes (LEDs, Biotable^®) and Photogem^®. Viability of the biofilms was evaluated by plate counts. To investigate treatment effects on dentine lesion formation, the treated biofilms were grown in a medium with low buffer capacity for an additional 24 h. Integrated mineral loss (IML) and lesion depth (LD) were assessed by transversal microradiography. Calcium release in the biofilm medium was measured by atomic absorption spectroscopy.

Results

Compared to the water treated control group, significant reduction in viability of S. mutans biofilms was observed when the combination of LEDs and Photogem^® was applied. LEDs or Photogem^® only did not result in biofilm viability changes. Similar outcomes were also found for dentine lesion formation. Significant lower IML and LD values were only found in the group subjected to the combined treatment of LEDs and Photogem^®. There was a good correlation between the calcium release data and the IML or LD values.

Conclusions

The high-throughput active attachment biofilm model is applicable for evaluating novel caries-preventive agents on both biofilm and demineralization inhibition. PACT had a killing effect on 24 h S. mutans biofilms and could inhibit the demineralization process.     

Synergistic activity of lysozyme and antifungal agents against Candida albicans biofilms on denture acrylic surfaces

Denture related oral candidiasis is a recalcitrant fungal infection not easily resolved by topical antifungals. The antimycotic protein lysozyme, in saliva is an important host defense mechanism although its activity against Candida biofilms on denture acrylic has not been evaluated.

Objectives

(i) To establish a clinically relevant denture acrylic assay model to develop standardized Candida albicans biofilms, and (ii) assess the inhibitory effects of lysozyme alone and, the latter combined with antifungals (nystatin, amphotericin B, ketoconazole and 5-fluorocytosine) on sessile Candida cells and, finally (iii) to visualize the accompanying ultrastructural changes.

Design

The rotating-disc biofilm reactor was used to develop standardized 48 h Candida biofilms on acrylic discs in YNB/100 mM glucose medium and the biofilm metabolic activity was monitored using a tetrazolium reduction assay.

Results

The biofilm metabolic activity was similar in 18 identical denture acrylic discs (p < 0.05) thus validating the rotating-disc biofilm model. Very low concentrations of lysozyme (6.25 μg/ml) significantly (p < 0.01) inhibited Candida biofilm formation indicating that lysozyme may likely regulate intra-oral Candida biofilm development. Although 100 μg/ml lysozyme killed 45% of sessile Candida cells, further increasing its concentration (up to 240 μg/ml) had no such effect. Nystatin, amphotericin B, and ketoconazole in association with 100 μg/ml lysozyme exhibited effective synergistic killing of biofilm Candida in comparison to drug-free controls. Scanning electron and confocal scanning laser microscopy analysis confirmed the latter trends.

Conclusion

Our results indicate that agents found in biological fluids such as lysozyme could be a safe adjunct to antifungals in future treatment strategies for recalcitrant candidal infections.     

Effect of charge density of bonding agent containing a new quaternary ammonium methacrylate on antibacterial and bonding properties

Objective

Quaternary amine charge density is important because when the negatively charged bacteria contact the positive quaternary amine charge, the electric balance is disturbed and the bacterium could be disrupted. There has been no report on the effects of charge density on the antibacterial efficacy of dental bonding agents. The objective of this study was to synthesize a new quaternary ammonium methacrylate, and investigate the effects of charge density of bonding agent on bacteria early-attachment, biofilm colony-forming units (CFU) and dentin bond strength.

Methods

Dimethylaminododecyl methacrylate (DMAHDM) with an alkyl chain length of 16 was synthesized and mixed into Scotchbond Multi-Purpose adhesive and primer (SBMP) at mass fractions of 0%, 2.5%, 5%, 7.5%, and 10%. A microtensile dentin bond test was performed. The density of quaternary ammonium groups was measured using a fluorescein dye method. Streptococcus mutans (S. mutans) early-attachment was examined at 4 h, and biofilm colony-forming units (CFU) were measured at 2 days.

Results

All groups had similar microtensile bonding strengths (mean ± sd; n = 40) of about 60 MPa (p > 0.1). Quaternary amine charge density of bonding agents monotonically increased with increasing DMAHDM mass fraction. Bacteria early-attachment coverage greatly decreased with increasing DMAHDM content in the resin. Biofilm CFU at 10% DMAHDM was reduced by more than 4 log, compared to SBMP control. Charge density of bonding agent was inversely proportional to bacteria early-attachment coverage and biofilm CFU.

Significance

Increasing the quaternary amine charge density of dentin bonding agent resin was shown to greatly reduce S. mutans attachment and decrease biofilm CFU by four orders of magnitude, without compromising the dentin bond strength. The new DMAHDM is promising for use in bonding agents and other antibacterial restorative materials to inhibit caries.     

Relationship between daily habits, Streptococcus mutans, and caries among schoolboys

Objectives

The purpose of this study was to examine the associations between daily habits, Streptococcus mutans, and caries using International Caries Detection and Assessment System Caries Index (ICDAS CI); and compare it to the DMF index.

Subjects and methods

Altogether 122 children were examined and interviewed. Saliva and plaque samples were collected and analyzed by Dentocult SM^® Strip Mutans test. ICDAS CI was calculated by counting all ICDAS caries scores of all surfaces divided by total number of carious teeth.

Results

ICDAS CI was significantly (p < 0.01) and strongly associated with DMFT/dmft (ρ = 0.72), DMFS/dmfs (ρ = 0.72), total number of carious teeth (DT/dt) (ρ = 0.77), enamel caries surfaces (ρ = 0.61) and dentine caries surfaces (ρ = 0.75). Plaque S. mutans was significantly (p < 0.05) correlated with ICDAS CI and DT/dt. Children who brushed once a day or more had significantly lower ICDAS CI (p < 0.01). Children who consumed sweets or drank soft drinks more than once a day had significantly higher ICDAS CI (p < 0.05). No significant association was found between ICDAS CI and frequency of flossing, use of mouthrinse, or gum chewing.

Conclusion

ICDAS CI seems to have similar trends as DMF indices, but includes more information about the stage, severity, and progress of the caries lesions of the patient.     

The preventive effect of grape seed extract on artificial enamel caries progression in a microbial biofilm-induced caries model

Objectives

The aim of this study was to evaluate the effect of grape seed extract (GSE) on enamel caries lesion formation in an in vitro Streptococcus mutans biofilm model.

Methods

Enamel fragments were prepared from bovine incisors and divided into six treatment groups (n = 12): inoculated Brain Heart Infusion with 1% sucrose (BHIS), 1 mg/mL GSE, 2 mg/mL GSE, 3 mg/mL GSE, 10 ppm fluoride as NaF, and uninoculated BHIS. For biofilm formation, tooth fragments were incubated anaerobically in polystyrene 6-well tissue culture plates containing BHIS, the respective agents, and S. mutans (1 × 10⁵ CFU/mL) for 24 h at 37 °C. Culture medium was replaced with fresh BHIS and respective agents daily over a 7-day period. Following caries lesion formation, lesion depth (LD) and relative optical density (ROD) were determined by polarized light microscopy (PLM) and confocal laser scanning microscopy (CLSM), respectively, to evaluate lesion progression.

Results

LDs of the 2 mg/mL GSE group (122.86 ± 13.41 μm) and the 3 mg/mL GSE group (111.92 ± 11.39 μm) were significantly smaller than those of the 1 mg/mL GSE (198.33 ± 17.70 μm) and control groups (210.86 ± 15.50 μm) (p < 0.05). Compared with the 2 mg/mL and 3 mg/mL groups, the control and 1 mg/mL GSE groups showed significantly lower ROD values when depth was less than 200 μm, indicating greater mineral loss.

Conclusions

Dose-dependent GSE inhibits in vitro enamel caries formation due to its ability to suppress growth of S. mutans and the formation of bio?lm.

Clinical signi?cance

Grape seed extract may be a novel virulence-targeted natural antimicrobial agent for caries prevention.     

Cariogenic potential of commercial sweeteners in an experimental biofilm caries model on enamel

Objective

Scarce evidence is available on the cariogenic potential of the widely used commercial sweeteners. The aim of this study was to evaluate the effect of several sweeteners on enamel demineralisation and on the cariogenic properties of Streptococcus mutans biofilms in an artificial caries model.

Methods

S. mutans-UA159 biofilms were cultured on bovine enamel slabs and exposed to one of the following commercial sweeteners in tablet or powder form: stevia, sucralose, saccharin, aspartame or fructose. Ten percent sucrose and 0.9% NaCl were used as caries-positive and caries-negative controls, respectively. Slabs/biofilms were exposed to the sweeteners three times per day for 5 min each time. After 5 days, biofilms were recovered to determine: biomass, bacterial counts and intra- and extracellular polysaccharides. Surface microhardness was measured before and after the experiment to assess enamel demineralisation, expressed as percentage of surface hardness loss (%SHL). Data were analysed using analysis of variance (ANOVA) and Bonferroni (p < 0.05).

Results

All tested commercial sweeteners, except fructose, showed less enamel demineralisation than sucrose (p < 0.05). Only saccharine showed less biomass and intracellular polysaccharides than the rest of the groups (p < 0.05). Stevia, sucralose and saccharine reduced the number of viable cells when compared with sucrose (p < 0.05). All sugar alternatives reduced extracellular polysaccharide formation when compared with sucrose (p < 0.05).

Conclusions

Most commercial sweeteners appear to be less cariogenic than sucrose, but still retaining some enamel demineralisation potential. Products containing stevia, sucralose and saccharine showed antibacterial properties and seem to interfere with bacterial metabolism. Further studies are necessary to deepen these findings.     

Antibacterial effect of ozone on cariogenic bacterial species

Objective

The aim was to evaluate the antibacterial effect of ozone on cariogenic bacterial species with and without the presence of saliva and a possible effect on the salivary proteins.

Methods

Suspensions of Actinomyces naeslundii (ACTCC 12104^T), Lactobacilli casei (N CTC 151) and Streptococcus mutans (NCTC 10449), in salt buffer or in saliva, were exposed to ozone gas delivered by the ozone generator Healozone™ 2130C. Aliquots of the suspensions were taken after 10, 30 and 60 s ozone exposures and cultivated on agar plates. Initial number of bacteria per ml was 8.0 × 10⁷ (SD 2.2 × 10⁷) (A. naeslundii), 1.0 × 10⁸ (SD 3.1 × 10⁶) (L. casei) and 1.0 × 10⁸ (SD 7.0 × 10⁵) (S. mutans), respectively. The proteins were separated by SDS electrophoresis and visualized by silver staining.

Results

In salt buffer 92%, 73% and 64% of the initial numbers of A. naeslundii, S. mutans and L. casei, respectively, were killed already after 10 s ozone exposure, while approximately 99.9% of the bacteria were dead after a 60 s exposure. After 10 and 30 s, but not after 60 s exposure to ozone, S. mutans and L. casei were less efficiently killed in saliva compared to the salt buffer. Various saliva proteins were degraded by ozone after a 60 s exposure.

Conclusions

The cariogenic species S. mutans, L. casei and A. naeslundii were almost eliminated following 60 s of ozone treatment. This killing was reduced in the presence of saliva although increasing the ozone application time to 60 s overcame these reductants in saliva. Detection of altered salivary proteins indicates that saliva components constitute additional targets for ozone.     

In vitro antimicrobial effect of bacteriocin PsVP-10 in combination with chlorhexidine and triclosan against Streptococcus mutans and Streptococcus sobrinus strains

Objectives

To determine the minimal inhibitory concentrations (MICs) of bacteriocin PsVP-10, chlorhexidine and triclosan on S. mutans and S. sobrinus and to study the potential synergistic combination between these antimicrobial and the bacteriocin PsVP-10.

Design

Were determined MICs of bacteriocin PsVP-10, triclosan and chlorhexidine on strains of S. mutans and S. sobrinus, which formed a biofilm or did not form a biofilm. In addition, the synergistic effect was analysed by the determination of respective fractionary inhibitory concentrations (FICs) between bacteriocin PsVP-10 plus chlorhexidine and bacteriocin PsVP-10 plus triclosan.

Results

MICs of three antimicrobials used were higher in those bacterial strains, which formed a biofilm. An interesting synergistic effect on both studied species was observed when bacteriocin and chlorhexidine were combined. A slighter synergy was determined for the combination bacteriocin PsVP-10 and triclosan.

Conclusions

The results showed that the combination of chlorhexidine bacteriocin PsVP-10 could reduce the number of cariogenic bacteria for in vitro studies. In the future this synergistic combination could be an alternative to antimicrobial therapy against S. mutans or S. sobrinus.     

Evaluation of the Antibacterial Efficacy of Silver Nanoparticles against Enterococcus faecalis Biofilm

Introduction

The purpose of this study was to evaluate the antibacterial efficacy of silver nanoparticles (AgNPs) as an irrigant or medicament against Enterococcus faecalis biofilms formed on root dentin.

Methods

Dentin sections were inoculated with E. faecalis for 4 weeks to establish a standard monospecies biofilm model. These biofilms were tested in 2 stages. In stage 1, the biofilms were irrigated with 0.1% AgNP solution, 2% sodium hypochlorite, and sterile saline for 2 minutes, respectively. In stage 2, the biofilms were treated with AgNP gel (0.02% and 0.01%) and calcium hydroxide for 7 days. The ultrastructure of one half of the specimens from each group was evaluated by using scanning electron microscopy, whereas the structure and distribution of viable bacteria of the other half of the specimens were assessed with confocal laser scanning microscopy combined with viability staining.

Results

Syringe irrigation with 0.1% AgNP solution did not disrupt the biofilm structure, and the proportion of viable bacteria in the biofilm structures was not different from that of the saline group (P > .05) but was less than that of the control group (P < .05). The biofilms treated with 0.02% AgNP gel as medicament significantly disrupted the structural integrity of the biofilm and resulted in the least number of post-treatment residual viable E. faecalis cells compared with 0.01% AgNP gel and calcium hydroxide groups (P < .05).

Conclusions

The findings from this study suggested that the antibiofilm efficacy of AgNPs depends on the mode of application. AgNPs as a medicament and not as an irrigant showed potential to eliminate residual bacterial biofilms during root canal disinfection.     

Parylene coating hinders Candida albicans adhesion to silicone elastomers and denture bases resin

Objective

To investigate whether parylene coatings over denture bases and silicone elastomers can effectively reduce Candida albicans adhesion and thus to decrease the incidence of denture stomatitis.

Design

Specimens of silicone elastomers A-2186 or lucitone 199 resin were prepared, and the measurements of contact angle, assay of XTT reduction and cell count of C. albicans adhesion were taken before and after parylene treatment. Furthermore, morphology of C. albicans adhesion for 48 h was observed by scanning electron microscope (SEM), and C. albicans adhesion for 4 h was illustrated by confocal scanning laser microscopy (CLSM) in combination with fluorescent dyes FUN-1 and Concanavalin A.

Result

There was a statistical difference between mean contact angles of silicone elastomer A-2186 before and after parylene coating (P < 0.05). The amount of C. albicans adhesion to the surface of silicone elastomer A-2186 and lucitone 199 resin after parylene treatment was significantly less than before parylene treatment by cells count and XTT reduction assay (P < 0.05). In SEM and CLSM analysis, C. albicans biofilm was more apt to generate on the surface of silicone elastomer A-2186 than other three groups, and more C. albicans aggregation formed on the surface of silicone elastomer A-2186 and lucitone 199 resin before parylene treatment than after parylene treatment.

Conclusion

Parylene coating reduced C. albicans adhesion and aggregation on the surface of silicone elastomer A-2186 and lucitone 199 resin, and improved the wettability of silicone elastomer A-2186.