Effect of dentin treatment on in vitro root tubule bacterial invasion.

In light of the in vitro S. sanguis bacterial migration observed deep into root dentin, an in vitro system was developed to determine the viability of these bacteria at the end of migration. Also of interest is whether the smear layer formed during root canal instrumentation modifies migration into root dentinal tubules. Forty-eight bovine root dentin samples were randomly split into two groups. Group 1 dentin blocks were not instrumented and were treated with 17% ethylenediamine tetraacetic acid and 2.5% sodium hypochlorite for 4 minutes in an ultrasonic bath Group 2 root canals were conventionally instrumented. The smear layer formed was not removed. Dentin blocks were inoculated with a S. sanguis National Collection of Type Culture 7863 suspension. Each sample was immersed in a receiver broth, incubated at 37 degrees C, and checked daily for 14 days. After a 14-day incubation period, group 1 S. sanguis cells remained viable and capable of inoculating the receiver medium after migration through the tubules. Group 2 cells, where the smear layer was intact, revealed an absence of S. sanguis migration in 88% of the cases. It is therefore plausible that smear layer on canal walls limits S. sanguis penetration of dentinal tubules in vitro.