Methods: The invasion of dentinal tubules by E. faecalis (erythromycin resistant strain, JH2-2 carrying plasmid pGh9:ISS1) was measured ex vivo after 8 weeks of incubation. The canal wall of extracted human root sections was either intact or instrumented, with or without smear layer present. Extent and maximum depth of tubule invasion were assessed histologically and compared between groups. In the binding study, vertically split root samples were prepared to expose longitudinally aligned dentinal tubules and fractured orthodentin. Surfaces were exposed to E. faecalis and incubated aerobically for 2 hours. Samples were processed for analysis using scanning electron microscopy. Bacterial binding to tubule walls versus fractured orthodentin was calculated as number of cells/100 µm2.
Results: It was confirmed that the strain of E. faecalis used in this study showed moderate to heavy tubule invasion after 8 weeks. Tubule invasion was significantly inhibited by the presence of smear layer (ANOVA, p<0.001). In the binding studies, significantly more bacteria bound to fractured orthodentin than to dentinal tubule wall (ANOVA, p<0.001). With respect to the tubule wall, binding was greater in inner versus outer dentine (p=0.02) and required metabolic activity for maximal binding. Conclusion: Although E. faecalis readily invaded tubules, it did not bind preferentially to tubule walls. Other factors may contribute to E. faecalis initial colonization of dentinal tubules.