In vitro demineralization prevention by fluoride and silver nanoparticles when applied to sound enamel and enamel caries-like lesions of varying severities.

OBJECTIVES: To investigate the effect of fluoride and silver nanoparticles on the prevention of in vitro demineralization of sound enamel and enamel caries-like lesions of varying severities. METHODS: Caries-like lesions of different severities (1/6/15 days) were created in bovine enamel specimens. One group remained sound. All specimens were demineralized again using a partially saturated acetic acid solution. Mimicking the intra-oral retention of fluoride and silver in vitro, this solution was supplemented with fluoride (0/1/10 ppm) and/or silver nanoparticles (0/10 ppm) in a factorial design. Changes in lesion depth (ΔL) and integrated mineral loss (ΔΔZ) were evaluated by digital transverse microradiography. Data was analyzed using three-way ANOVA. RESULTS: Lesion severity significantly affected ΔΔZ and ΔL, after no treatment and after the treatment of fluoride and silver independently (p = 0.012 and p = 0.037, respectively). Fluoride and the fluoride × lesion severity interaction were shown to be significant (p < 0.001) on ΔΔZ and ΔL. Silver nanoparticles significantly affected ΔΔZ (p = 0.041), but not ΔL (p = 0.15). The silver nanoparticles × lesion severity interaction was significant for ΔΔZ and ΔL (p = 0.032 and p = 0.024, respectively). No interaction was observed for ΔΔZ and ΔL between fluoride and silver (p = 0.962 and p = 0.971, respectively) as well as lesion severity and the use of fluoride and silver combined (p = 0.722 and p = 0.158, respectively). CONCLUSION: Fluoride and silver nanoparticles had a significant effect on the prevention of in vitro demineralization of sound enamel and enamel caries-like lesions of varying severities. CLINICAL SIGNIFICANCE: Fluoride and silver nanoparticles may potentially allow for more tailored caries prevention.

Light Energy Dose and Photosensitizer Concentration Are Determinants of Effective Photo-Killing against Caries-Related Biofilms.

Caries-related biofilms and associated complications are significant threats in dentistry, especially when biofilms grow over dental restorations. The inhibition of cariogenic biofilm associated with the onset of carious lesions is crucial for preventing disease recurrence after treatment. This in vitro study defined optimized parameters for using a photosensitizer, toluidine blue O (TBO), activated via a red light-emitting diode (LED)-based wireless device to control the growth of cariogenic biofilms. The effect of TBO concentrations (50, 100, 150, and 200 µg/mL) exposed to light or incubated in the dark was investigated in successive cytotoxicity assays. Then, a mature Streptococcus mutans biofilm model under sucrose challenge was treated with different TBO concentrations (50, 100, and 150 µg/mL), different light energy doses (36, 108, and 180 J/cm2), and different incubation times before irradiation (1, 3, and 5 min). The untreated biofilm, irradiation with no TBO, and TBO incubation with no activation represented the controls. After treatments, biofilms were analyzed via S. mutans colony-forming units (CFUs) and live/dead assay. The percentage of cell viability was within the normal range compared to the control when 50 and 100 µg/mL of TBO were used. Increasing the TBO concentration and energy dose was associated with biofilm inhibition (p < 0.001), while increasing incubation time did not contribute to bacterial elimination (p > 0.05). Irradiating the S. mutans biofilm via 100 µg/mL of TBO and ≈180 J/cm2 energy dose resulted in ≈3-log reduction and a higher amount of dead/compromised S. mutans colonies in live/dead assay compared to the control (p < 0.001). The light energy dose and TBO concentration optimized the bacterial elimination of S. mutans biofilms. These results provide a perspective on the determining parameters for highly effective photo-killing of caries-related biofilms and display the limitations imposed by the toxicity of the antibacterial photodynamic therapy's chemical components. Future studies should support investigations on new approaches to improve or overcome the constraints of opportunities offered by photodynamic inactivation of caries-related biofilms.

pH-responsive calcium and phosphate-ion releasing antibacterial sealants on carious enamel lesions in vitro.

OBJECTIVE: Nanoparticles of amorphous calcium phosphate (NACP) have shown beneficial effects of a robust release of calcium and phosphate ions at low pH. Here we examined the effect of NACP combined into antibacterial/rechargeable sealant formulations on the mineral content of artificial carious enamel during pH-cycling mimicking intraoral conditions. MATERIALS AND METHODS: NACP and a quaternary ammonium methacrylate (DMAHDM) were synthesized. Three resin sealants were formulated: "base formulation" (without NACP and DMAHDM, used as control); "NACP on the base formulation" (with 20 wt.% NACP); "NACP on the antibacterial formulation" (with 20 wt.% NACP and 5 wt.% DMAHDM). Standardized enamel windows on sealed non-carious human molars were demineralized and randomly divided into four groups: three groups of teeth sealed with the experimental materials and one group of teeth without sealant application used as negative control. The teeth were exposed to pH cycling regime. The changes in the mineral content of enamel were assessed by quantitative surface hardness loss in percentage (%SHL) and qualitative analyses via scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) and polarized light microscopy (PLM). RESULTS: The contact with NACP-containing formulations provoked significant lower %SHL on sealed enamel (p < 0.05) in comparison to control groups. This outcome was supported by the results of SEM-EDX, in which the enamel presented higher percentages of calcium and phosphate than control groups. PLM showed less enamel superficial demineralization around the sealants containing NACP. CONCLUSION: NACP incorporated into an antibacterial sealant protected the enamel against demineralization. pH-responsive calcium and phosphate-ion releasing sealants with antimicrobial and rechargeable properties may be a reliable complementary approach for caries management. CLINICAL SIGNIFICANCE: Dental caries is the most common childhood disease. Enamel demineralization represents the initial stage of carious lesion formation and may lead to invasive dental procedures. We explored the role of amorphous calcium phosphate (NACP) in a newly-developed antibacterial and rechargeable dental sealant formulation as a preventive approach.

Multifunctional antibacterial dental sealants suppress biofilms derived from children at high risk of caries.

Dental caries in children is a leading worldwide oral health concern. Combining antibacterial and remineralizing additives within dental sealants is a promising approach for caries prevention. Saliva contains oral bacteria that are indicative of the whole oral microbiome and may have the ability to reflect the dysbiosis present in patients with dental caries. Here, we used the saliva of children at a low and high risk of caries to culture microcosm biofilms resembling caries-associated microbial communities and investigated the changes in the biofilms promoted by the formulated dental sealants containing dimethylaminohexadecyl methacrylate (DMAHDM), a quaternary ammonium monomer, and nanoparticles of amorphous calcium phosphate (NACP). Ten volunteers were selected from each caries-risk condition for saliva collection. Biofilms were grown on the tested sealant samples using a 48 h-microcosm biofilm model. The biofilm growth, metabolic behavior, and bacterial acid production were combined with 16S rRNA sequencing analysis for the assessment of the biofilm grown over the material. The DMAHDM-NACP dental sealant formulations promoted a significant reduction in the population of mutans streptococci, total streptococci, lactobacilli, and total microorganisms in the biofilms regardless of the risk status of the donor child's saliva (p < 0.05). Metabolic and lactic acid production was greatly reduced when in contact with the DMAHDM-NACP sealants in both the sources of inoculum. The relative abundance of the Streptococcus genera derived from patients at a high risk of caries was reduced on contact with the antibacterial sealant. The dental sealant formulations were effective in modulating the growth of the biofilm derived from the saliva of children at a low and high risk of caries. The sealants formulated herein with dual functions and purpose for biointeractivity to prevent biofilm formation and mineral loss can be a reliable complementary strategy to decrease the incidence of carious lesions in children at a high risk of caries.

Inhibition of nicotine-induced Streptococcus mutans biofilm formation by salts solutions intended for mouthrinses.

OBJECTIVES: Biofilm formation is critical to dental caries initiation and development. The aim of this study was to investigate the effects of nicotine exposure on Streptococcus mutans (S. mutans) biofilm formation concomitantly with the inhibitory effects of sodium chloride (NaCl), potassium chloride (KCl) and potassium iodide (KI) salts. This study examined bacterial growth with varying concentrations of NaCl, KCl, and KI salts and nicotine levels consistent with primary levels of nicotine exposure. MATERIALS AND METHODS: A preliminary screening experiment was performed to investigate the appropriate concentrations of NaCl, KCl, and KI to use with nicotine. With the data, a S. mutans biofilm growth assay was conducted using nicotine (0-32 mg/mL) in Tryptic Soy broth supplemented with 1% sucrose with and without 0.45 M of NaCl, 0.23 M of KCl, and 0.113 M of KI. The biofilm was stained with crystal violet dye and the absorbance measured to determine biofilm formation. RESULTS: The presence of 0.45 M of NaCl, 0.23 M of KCl, and 0.113 M of KI significantly inhibited (p < 0.05) nicotine-induced S. mutans biofilm formation by 52%, 79.7%, and 64.1%, respectively. CONCLUSIONS: The results provide additional evidence regarding the biofilm-enhancing effects of nicotine and demonstrate the inhibitory influence of these salts in reducing the nicotine-induced biofilm formation. A short-term exposure to these salts may inhibit S. mutans biofilm formation.