Is it really penetration? Locomotion of devitalized Enterococcus faecalis cells within dentinal tubules of bovine teeth

•DAPI provides information about bacterial penetration into dentinal tubules.•Increased exposure of devitalized bacteria lead to more penetrated tubules.•Increased exposure time of devitalized bacteria lead to a deeper tubule-migration.

ObjectiveThe aim of the present study was to evaluate the penetration characteristics of devitalized and vital E. faecalis cells into root dentinal tubules.DesignThirteen root canals were incubated with devitalized (4 days, 7 days, 14 days, 28 days) and vital (28 days) E. faecalis strains (streptomycin-resistant strains) after root canal enlargement (size 80, taper 0.02) with 3 % NaOCl solution. The smear layer was intentionally removed with 20 % EDTA before inoculation. Samples were processed for analysis by scanning electron microscopy (SEM) and DAPI (4′,6-diamidino-2-phenylindole) staining. DAPI was conducted for fluorescence microscopic visualization of the bacterial penetration into dentinal tubules. The penetration depth was calculated with the measurement tool of the Axio Vision program (Zeiss, Jena, Germany).ResultsDevitalized E. faecalis strains were able to penetrate into dentinal tubules of the root canal. Apikal penetration depths of the devitalized cells were 100.67 μm ± 26.54 μm after 7 days, 230.67 μm ± 111.5 μm after 14 days and 266.5 μm ± 92.63 μm after 28 days of incubation. The total number and penetration depth of E. faecalis cells was lower compared to a vital suspension of E. faecalis (1002.45 μm) after 28 days. It was noted that bacterial penetration was not common to all of the dentinal tubules in the vital E. faecalis control and especially in the devitalized control.ConclusionsIncreased exposure times of devitalized bacteria into root canals lead to an increased number of penetrated dentinal tubules as well as to a deeper penetration.