Does recharging dental restorative materials with fluoride influence biofilm formation?

Objectives: To investigate the influence of recharging dental restorative materials with fluoride on biofilm formation. Methods: Specimens produced from a high-viscosity glass ionomer cement (HVGIC), a resin-modified glass ionomer cement (RMGIC), and a resin-based composite (RBC) were randomly allotted to incubation in artificial saliva either for one week (AS-1), for five weeks (AS-5), for five weeks including twice/day brushing with 1450 ppm NaF toothpaste (AS-5-brush), or one-time exposition to 5000 ppm NaF after five weeks of incubation (AS-5-exp). Human enamel was used as reference. Surface roughness and the release of fluoride from the specimens was determined; biofilm formation was simulated using mono- or multispecies microbiological models and analysed employing an MTT-based approach and confocal laser-scanning microscopy. Results: Monospecies biofilm formation was significantly reduced on HVGIC in comparison to RMGIC and RBC. It was also reduced on HVGIC and enamel after treatment with fluoride in groups AS-5-brush and AS-5-exp in comparison to AS-5. These effects were particularly pronounced after 24 h, and less pronounced after 48 h of biofilm formation. In the multispecies microbiological model, similar observations were identified for HVGIC, while for enamel a significant reduction in biofilm formation was observed in groups AS-5-brush and AS-5-exp. No significant effect of fluoride treatments was identified for RMGIC and RBC, regardless of the microbiological model applied. Significance: These data indicate that biofilm formation on the surfaces of a glass ionomer cement and enamel can be relevantly influenced by treatment with fluoride. Enamel may serve as a fluoride reservoir which requires regular recharge.