Hydrophilicity of dentin bonding systems influences in vitro Streptococcus mutans biofilm formation

Objective

To evaluate in vitro Streptococcus mutans (S. mutans) biofilm formation on the surface of five light-curing experimental dental bonding systems (DBS) with increasing hydrophilicity. The null hypothesis tested was that resin chemical composition and hydrophilicity does not affect S. mutans biofilm formation.

Methods

Five light-curing versions of experimental resin blends with increasing hydrophilicity were investigated (R₁, R₂, R₃, R₄ and R₅). R₁ and R₂ contained ethoxylated BisGMA/TEGDMA or BisGMA/TEGDMA, respectively, and were very hydrophobic, were representative of pit-and-fissure bonding agents. R₃ was representative of a typical two-step etch-and-rinse adhesive, while R₄ and R₅ were very hydrophilic resins analogous to self-etching adhesives. Twenty-eight disks were prepared for each resin blend. After a 24 h-incubation at 37 °C, a multilayer monospecific biofilm of S. mutans was obtained on the surface of each disk. The adherent biomass was determined using the MTT assay and evaluated morphologically with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM).

Results

R₂ and R₃ surfaces showed the highest biofilm formation while R₁ and R₄ showed a similar intermediate biofilm formation. R₅ was more hydrophilic and acidic and was significantly less colonized than all the other resins. A significant quadratic relationship between biofilm formation and hydrophilicity of the resin blends was found. CLSM and SEM evaluation confirmed MTT assay results.

Conclusions

The null hypothesis was rejected since S. mutans biofilm formation was influenced by hydrophilicity, surface acidity and chemical composition of the experimental resins. Further studies using a bioreactor are needed to confirm the results and clarify the role of the single factors.