Effect of different dentin adhesives on bacteria growth inhibition

Objectives: Determine how different dentin adhesives inhibit endodontic pathogens immediately after curing or after storage in distilled water for 7 days.

Methods: Investigated bacterial strains were Fusobacterium nucleatum (FN), Prevotella nigrescens (PN), Enterococcus faecalis (EF) and Streptococcus mutans (SM). After cultivation in PYG broth, 100 µL of FN,PN, and EF were placed on TS blood agar plates, while SM was incubated on BHI plates. Blank paper discs, diameter=6mm, were saturated with 25 µL of each adhesive system and cured. The adhesives tested were Scotchbond (SB), Single Bond Plus Adhesive (SI), Clearfil SE Bond (CF), and iBond (IB). Three different main groups were investigated: Group1) Phosphoric acid 50% served as control, Group2) Cured adhesive, Group3) Cured adhesive stored in distilled water for 7 days. The phosphoric acid was in liquid form. The plates were incubated in an anaerobic chamber for 3 days. The plates with S. mutans were incubated in a CO₂ chamber for 3 days. After completed incubation, the zones of inhibition were measured with the NIH Imaging Software. The inhibition areas to the disk areas of the different groups/adhesives were evaluated with ANOVA.

Results: The results revealed significant differences between the different group types (groups 1, 2 and 3), bacteria strains and adhesive materials (p<0.0001). The phosphoric acid gave the strongest inhibition, the newly cured an intermediary effect, while those stored in water for 7 days the lowest (p<0.05). The bacteria showing the strongest response were PN > FN >SM and EF (p<0.05). Of the four adhesives, CF>SI>SB>IB (p<0.05). Significant interactions existed between materials and bacteria strains (p<0.0001).

Conclusion: The results revealed that dentin adhesives have a bacteriostatic effect, particularly on PN and FN, while their effect on EF was least pronounced. The acidity of an adhesive does not necessry imply superior bacteriostatic effect.