Synergistic antimicrobial effect of calcium strontium silicate and sodium-fluoride varnish on cariogenic biofilms

Abstract

Objectives: To investigate the effect of combined novel calcium strontium silicate (CSR) and sodium fluoride (NaF) varnish on dual-species Streptococcus mutans (S.mutans) and Lactobacillus acidophilus (L.acidophilus) biofilm. Methods: The CSR was synthesized by the sol-gel process and incorporated in 5% NaF varnish at 3 different concentrations (1%, 2%, and 4% by wt.). The treatment/control groups were: 1% CSR-NaF, 2% CSR-NaF, 4% CSR-NaF, NaF, and no treatment. The release of Ca, Sr, and Si in the extraction medium (0.9% NaCl) was measured by inductively coupled plasma optical emission spectroscopy. The F release was measured by the fluoride ion-selective electrode. The biofilms of S.mutans and L.acidophilus (1:1) were grown on sterilized hydroxyapatite discs for 24 h and subjected to treatment with experimental varnish extracts for 30 min. Before and after treatment, a cariogenic challenge (10% sucrose in BHI) was given. The biofilms were stained to determine live/dead bacterial proportions using confocal laser scanning microscopy. Colony-forming units (CFU) of S.mutans and L.acidophilus were evaluated from biofilm supernatants incubated on selective media agar plates. One-way ANOVA with Bonferroni’s post-hoc test was used for statistical analysis at α=0.05. Results: The release of Ca, Sr, and Si significantly increased with increasing concentrations of CSR in NaF. The F release was higher in all CSR-NaF groups than NaF (p<0.001). Confocal imaging results showed that 4% CSR-NaF presented significantly higher proportions of dead cells than NaF (p<0.05). The CFU for S.mutans were significantly lower in 4% CSR-NaF compared to NaF (p<0.001); while for L.acidophilus were significantly lower in 2% and 4% CSR-NaF than NaF (p<0.05), and (p<0.001) respectively. Conclusions: Incorporating 4% CSR in NaF varnish enhanced the antimicrobial effect of NaF varnish on dual-species biofilm.