Evaluation of Streptococcus mutans biofilms formed on fluoride releasing and non fluoride releasing resin composites

Abstract

Objectives: The aim of this study was to evaluate the acid production, acid tolerance and composition of Streptococcus mutans biofilms formed on fluoride releasing and non fluoride releasing resin composites.

Methods: S. mutans biofilms were formed on saliva-coated discs prepared from fluoride releasing (Unifil Flow and F2000) or non fluoride releasing materials (Filtek Z350, GRADIA DIRECT and hydroxyapatite). To assess the level of acid production and acid tolerance, glycolytic pH drop and proton permeability assays were performed using 94h old S. mutans biofilms. To evaluate the biofilm composition, the biomass (total dry-weight), colony forming unit (CFU), water-insoluble extracellular polysaccharides (EPS), water-soluble EPS and intracellular iodophilic polysaccharides (IPS) of 94 h old S. mutans biofilms were analysed. The amount of fluoride of old culture medium released from the materials during the experimental period was also determined. Each assay was performed in duplicate in at least four different experiments (n=8).

Results: All biofilms showed similar initial rates of acid production (0.083-0.089 pH drop/min) and proton permeability (0.025-0.036 pH increase/min), irrespective of fluoride release from the materials. On the other hand, the amount of biomass, water-insoluble EPS and IPS of the biofilms on Unifil Flow, which releases a larger amount of fluoride in the early stages of biofilm formation, were significantly lower than those on the other materials (up to 27%, 38% and 36% reduction in biomass, water-insoluble and IPS, respectively).

Conclusions: Our finding suggests that fluoride releasing resin composites might contribute to the decrease in cariogenic composition of S. mutans biofilms if an appropriate amount of fluoride is released in the early stages of biofilm formation.