Early in vitro mutans streptococci colonization on different experimental resins

Objectives: The aim of this study was to evaluate surface colonization by mutans streptococci (Ms) of five light-curing experimental resins with increasing hydrophilicity. The tested hypothesis was that adhesive hydrophilicity does not affect bacteria colonization. Materials and methods: Five light-curing versions of neat experimental resin blends with increasing hydrophobicity were investigated (R1, R2, R3, R4 and R5). R1 and R2 contained ethoxylate or BisGMA/TEGDMA, respectively, and were very hydrophobic, similarly to pit-and-fissure sealants. R3was representative of a typical two-step etch-and-rinse adhesive, while R4 and R5 were similar to self-etching very hydrophilic resins containing carboxylic or phosphoric acid methacrylates, respectively. 13 disks (6.4mmdiameter and 1.5mmthick)were obtained for each of the formulations and polymerized with a lightcuring unit (Spectrum 800, DENTSPLY) for 80 s at 800mW/cm2. Disks were finished using silicon carbide paper and stored in PBS for 72 h to allow leaching of unreacted monomers. Specimens were then sterilized and a 48-h incubation Ms monospecific biofilm was obtained on disk surfaces. The amount of viable biomass adherent to the surface of each disk was determined using a colorimetric technique (MTT assay) and spectrophotometric analysis by optical density (OP). Results: R1 group showed the lowest OP values for bacterial colonization while R4 and R5 demonstrated the highest ones (ANOVA, p < 0.0001). An increasing trend of Ms colonization from R1 to R5, as resin hydrophobicity increases, was found. Resin type Mutans streptococci R1 1.085 ± 21.4a R2 1.660 ± 36.7b R3 1.664 ± 42.8b R4 1.929 ± 19.4c R5 1.932 ± 20.6c Different superscript letters indicate statistical differences (p < 0.05). Conclusions: The tested hypothesis was rejected since Ms surface colonization was influenced by hydrophilicity of the experimental resins. Lower hydrophilicity corresponded to lower Ms surface colonization. Further studies should confirm the ability of Ms to colonize resin surfaces in vivo.