Analysis of the mechanical stability and surface detachment of mature Streptococcus mutans biofilms by applying a range of external shear forces.

Well-established biofilms formed by Streptococcus mutans via exopolysaccharide matrix synthesis are firmly attached to tooth surfaces. Enhanced understanding of the physical properties of mature biofilms may lead to improved approaches to detaching or disassembling these highly organized and adhesive structures. Here, the mechanical stability of S. mutans biofilms was investigated by determining their ability to withstand measured applications of shear stress using a custom-built device. The data show that the initial biofilm bulk (~ 50% biomass) was removed after exposure to 0.184 and 0.449 N m(-2) for 67 and 115 h old biofilms. However, removal of the remaining biofilm close to the surface was significantly reduced (vs initial bulk removal) even when shear forces were increased 10-fold. Treatment of biofilms with exopolysaccharide-digesting dextranase substantially compromised their mechanical stability and rigidity, resulting in bulk removal at a shear stress as low as 0.027 N m(-2) and > a two-fold reduction in the storage modulus (G'). The data reveal how incremental increases in shear stress cause distinctive patterns of biofilm detachment, while demonstrating that the exopolysaccharide matrix modulates the resistance of biofilms to mechanical clearance.

Boron-containing coating yields enhanced antimicrobial and mechanical effects on translucent zirconia.

OBJECTIVES: To evaluate the mechanical and antimicrobial properties of boron-containing coating on translucent zirconia (5Y-PSZ). METHODS: 5Y-PSZ discs (Control) were coated with a glaze (Glaze), silver- (AgCoat), or boron-containing (BCoat) glasses. The coatings' antimicrobial potential was characterized using S. mutans biofilms after 48 h via viable colony-forming units (CFU), metabolic activity (CV) assays, and quantification of extracellular polysaccharide matrix (EPS). Biofilm architectures were imaged under scanning electron and confocal laser scanning microscopies (SEM and CLSM). The cytocompatibility was determined at 24 h via WST-1 and LIVE&DEAD assays using periodontal ligament stem cells (PDLSCs). The coatings' effects on properties were characterized by Vickers hardness, biaxial bending tests, and fractography analysis. Statistical analyses were performed via one-way ANOVA, Tukey's tests, Weibull analysis, and Pearson's correlation analysis. RESULTS: BCoat significantly decreased biofilm formation, having the lowest CFU and metabolic activity compared with the other groups. BCoat and AgCoat presented the lowest EPS, followed by Glaze and Control. SEM and CLSM images revealed that the biofilms on BCoat were thin and sparse, with lower biovolume. In contrast, the other groups yielded robust biofilms with higher biovolume. The cytocompatibility was similar in all groups. BCoat, AgCoat, and Glaze also presented similar hardness and were significantly lower than Control. BCoat had the highest flexural strength, characteristic strength and Weibull parameters (σF: 625 MPa; σ0: 620 MPa; m = 11.5), followed by AgCoat (σF: 464 MPa; σ0: 478 MPa; m = 5.3). SIGNIFICANCE: BCoat is a cytocompatible coating with promising antimicrobial properties that can improve the mechanical properties and reliability of 5Y-PSZ.

Novel strategy of S. mutans gcrR gene over-expression plus antibacterial dimethylaminohexadecyl methacrylate suppresses biofilm acids and reduces dental caries in rats.

OBJECTIVE: Streptococcus mutans (S. mutans) is a major contributor to dental caries, with its ability to synthesize extracellular polysaccharides (EPS) and biofilms. The gcrR gene is a regulator of EPS synthesis and biofilm formation. The objectives of this study were to investigate a novel strategy of combining gcrR gene over-expression with dimethylaminohexadecyl methacrylate (DMAHDM), and to determine their in vivo efficacy in reducing caries in rats for the first time. METHODS: Two types of S. mutans were tested: Parent S. mutans; and gcrR gene over-expressed S. mutans (gcrR OE S. mutans). Bacterial minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were measured with DMAHDM and chlorhexidine (CHX). Biofilm biomass, polysaccharide, lactic acid production, live/dead staining, colony-forming units (CFUs), and metabolic activity (MTT) were evaluated. A Sprague-Dawley rat model was used with parent S. mutans and gcrR OE S. mutans colonization to determine caries-inhibition in vivo. RESULTS: Drug-susceptibility of gcrR OE S. mutans to DMAHDM or CHX was 2-fold higher than that of parent S. mutans. DMAHDM reduced biofilm CFU by 3-4 logs. Importantly, the combined gcrR OE S. mutans+ DMAHDM dual strategy reduced biofilm CFU by 5 logs. In the rat model, the parent S. mutans group had a higher cariogenicity in dentinal (Dm) and extensive dentinal (Dx) regions. The DMAHDM + gcrR OE group reduced the Dm and Dx caries to only 20 % and 0 %, those of parent S. mutans + PBS control group (p < 0.05). The total caries severity of gcrR OE + DMAHDM group was decreased to 51 % that of parent S. mutans control (p < 0.05). SIGNIFICANCE: The strategy of combining S. mutans gcrR over-expression with antibacterial monomer reducing biofilm acids by 97 %, and reduced in vivo total caries in rats by 48 %. The gcrR over-expression + DMAHDM strategy is promising for a wide range of dental applications to inhibit caries and protect tooth structures.

Rapid Antibiofilm Effect of Ag/ZnO Nanocomposites Assisted by Dental LED Curing Light against Facultative Anaerobic Oral Pathogen Streptococcus mutans.

The integration of nanomaterials with clinical therapeutic instruments is a promising approach to improve the effects of nanomaterials. We reported an efficient synergistic antibacterial strategy formed through the combination of Ag/ZnO nanocomposites with a light-emitting diode (LED) curing light, which is a commonly used small instrument in dental clinics. The as-designed integration depicted a significantly enhanced bactericidal effect on facultative anaerobic oral pathogen Streptococcus mutans (S. mutans) both in planktonic and biofilm phases over a very short irradiation time (≤5 min). Further study showed that the combination of LED and Ag/ZnO nanocomposites induced more ·OH and ·O2- generation, which is responsible for the enhanced antibacterial activity. Moreover, this combination could destroy S. mutans biofilm by killing the bacteria embedded within biofilm, inhibiting exopolysaccharide production and down-regulating the biofilm-related gene expression. Therefore, it is proposed that this combination could be applied in dental clinics to realize dental caries prevention and dental restoration simultaneously.

Cytotoxicity of novel fluoride solutions and their influence on mineral loss from enamel exposed to a Streptococcus mutans biofilm.

OBJECTIVE: This study evaluated the cytotoxicity, antimicrobial activity and in vitro influence of new fluoridated nanocomplexes on dental demineralization. DESIGN: The nanocomplexes hydroxypropyl-ß-cyclodextrin with 1% titanium tetrafluoride (TiF4) and γ-cyclodextrin with TiF4 were compared to a positive control (TiF4), a blank control (without treatment) and negative controls (hydroxypropyl-ß-cyclodextrin, γ-cyclodextrin, deionized water), following 12- and 72-hour complexation periods. The cytotoxicity was assessed using the neutral red dye uptake assay at T1-15 min, T2-30 min and T3-24 h. A minimum bactericidal concentration (MBC) against Streptococcus mutans (ATCC 25175) was performed. Enamel blocks were exposed to an S. mutans biofilm, and the percentage of surface microhardness loss was obtained. Biocompatibility and microhardness data were analysed using ANOVA/Tukey tests (p < 0.05). RESULTS: At T1, the cell viability results of the nanocomplexes were similar to that of the blank control. At T2 and T3, the 72 h nanocomplexes demonstrated cell viability results similar to that of the blank, while the 12 h solutions showed results different from that of the blank (p < 0.05). All fluoridated nanocompounds inhibited S. mutans (MBC = 0.25%), while the MBC of TiF4 alone was 0.13%. All fluoridated compounds presented a percentage of surface microhardness loss lower than that of deionized water (p < 0.05). CONCLUSIONS: The new fluoridated nanocomplexes did not induce critical cytotoxic effects during the experimental periods, whilst they did show bactericidal potential against S. mutans and inhibited enamel mineral loss.

Enhanced photodynamic therapy using light fractionation against Streptococcus mutans biofilm: type I and type II mechanism.

AIM: The objective of the study was to look the efficacy of fractionated light against Streptococcus mutans biofilm. MATERIALS & METHODS: Antibiofilm assays (crystal violet, congo red), electron microscopic, confocal and spectroscopic studies were performed to check the effect of fractionated light. RESULTS: 6-6.5 log10 reduction of planktonic and 3.6-4.2 log10 reduction in biofilm were observed after irradiation with fractionated as compared with continuous light. Increased permeability to propidium iodide and leakage of cellular constituent validate the greater antibiofilm effect of fractionated light. Spectroscopic studies confirmed the relative contribution of type I and type II photochemistry. CONCLUSION: Phenothiazinium dyes have a potential against bacterial biofilm in combination with light fractionation and it offers new opportunities to explore its clinical implication.