[Bacterial penetration of bovine dentinal tubules. 1]

The penetration by bacteria through dentinal tubules was studied using a device that included portion of bovine anterior teeth. Strains of 4 genera, Streptococcus mutans, Lactobacillus casei, Staphylococcus aureus and Escherichia coli, were used for the experiment, and the effects of acid etching of dentin on the penetration of bacteria through the dentin was examined. The time required for penetration through dentinal tubules of acid-etched samples was shorter than that of unetched samples. The minimum time required for half the samples to become positive for bacterial penetration through dentin MPT50 was 4 hours for all strains chosen when the acid-etched dentin was the target. In non-acid etched samples, the MPT50 varied among the genera and ranged from 20 hours to 48 hours; the speed of penetration was Sta. aureus = L. casei greater than Str. mutans greater than E. coli. Observation under the scanning electron microscope indicated that the smeared layer was completely coated on the surface of the prepared cavity, and when bacterial penetration occurred, a portion of the smear layer on the dentin disappeared. In longitudinal sections, the penetration by the bacteria into the tubules was visible. From these results, it is suggested that the smeared layer have an important effects on bacterial penetration through these tubules.