Long-term anti-cariogenic biofilm activity of glass ionomers related to fluoride release.

OBJECTIVES: The aim of this study was to evaluate the difference between anti-cariogenic biofilm activities of glass ionomers (G-Is) during the initial and second fluoride release phases and to define relationships between the anti-biofilm activities and fluoride release. METHODS: Fluoride release of three commercially available G-Is in a buffer was evaluated for 770 h, and then 70-h-old Streptococcus mutans UA159 biofilms were formed on the G-Is that had been immersed in the buffer for 0, 100, 200, or 700 h. The dry weight, bacterial cell number, water-insoluble extracellular polysaccharides (EPSs), and accumulated fluoride concentration of the 70-h-old biofilms and fluoride release and acid production rates during biofilm formation were determined. Relationships between the experimental variables and fluoride release rate were also evaluated using linear regression analysis. RESULTS: In this study, fluoride release of the tested G-Is did not exhibit a biphasic pattern during biofilm formation. The release was sustained or did not rapidly decrease even over long immersion periods and was strongly correlated with an increase in accumulated fluoride concentration of the biofilms (R=0.99, R(2)=0.98) and reductions in dry weight, water-insoluble EPSs, and acid production rate of the biofilms (R=-0.99 to -0.96, R(2)=0.92-0.98). CONCLUSIONS: This study suggests that G-Is can effectively affect acid production, EPS formation, and accumulation of cariogenic biofilms even during the second fluoride release phase, and that the anti-cariogenic biofilm activity is strongly correlated with fluoride release, which may be enhanced by acid production of cariogenic biofilms. CLINICAL SIGNIFICANCE: G-Is can affect cariogenic biofilm formation even during the second fluoride release phase.

Relationship between fluoride release rate and anti-cariogenic biofilm activity of glass ionomer cements.

OBJECTIVES: The aim of this study was to evaluate acidogenicity and composition of Streptococcus mutans biofilms on glass ionomer cements (GICs) and then to determine the relationship between the anti-S. mutans biofilm activity and fluoride release rate of the GICs. METHODS: S. mutans biofilms were formed on discs prepared using five commercial GICs. Acid production and fluoride release rates of the biofilms on the GIC discs during biofilm formation (0-94 h) were determined. Next, 94-h-old S. mutans biofilms on GIC discs were analyzed to evaluate the biofilm composition (dry weight, bacterial cell number, and extra-cellular polysaccharide (EPS) amount) using microbiological, biochemical, and confocal laser scanning microscopy (CLSM) methods. Lastly, relationships between the fluoride release rate and changes in acidogenicity and composition of the biofilms were determined using a linear-fitting procedure. RESULTS: All of the tested GICs released fluoride ions. Of the GICs, the two that showed the highest fluoride release rates strongly affected acidogenicity, dry weight, and EPS formation of the biofilms. Furthermore, they reduced the bacterial and EPS bio-volumes and EPS thickness. However, the number of colony forming units (CFUs) of the biofilms was higher than that of the control. Generally, changes in the acidogenicity and composition (except for CFU count) of the biofilms on the GICs followed a negative linear-pattern of fluoride release rate-dependence (R=-0.850 to -0.995, R(2)=0.723-0.990). SIGNIFICANCE: These results suggest that the anti-cariogenic biofilm activity of GICs is closely correlated with their fluoride release rate during biofilm formation.

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.