[In vitro study of bacterial invasion in radicular dentin]

The purpose of this study was to investigate whether plaque bacteria invade exposed radicular dentin after root planing or chemical root treatment in vitro. Pieces of dentin were cut out from impacted third molars. The surface of all dentin pieces was treated with sandpaper (#240) so as to make the surface roughness of dentin pieces equal to that of the root surface after root planing (RP surface). Half of the dentin pieces were treated with citric acid (pH 1.0) for 3 minutes (CA surface). After sterilization, each dentin piece was incubated at 37 degrees C in a culture medium inoculated with either S. mutans or S. sanguis. After 1, 3, 7 and 28 days of incubation, the invasion of microorganisms into the dentinal tubules was histologically examined using a light microscope. The following results were obtained. 1. The invasion of S. mutans and S. sanguis into the dentinal tubules was observed at 1, 3, 7 and 28 days. The depth and number of bacterial invasion into the dentinal tubules were positively correlated with incubation time on CA surfaces but not with RP surfaces. 2. The depth and the number of bacterial invasion into the dentinal tubules were higher on the CA surfaces than the RP surfaces. 3. Since the citric acid treatment of scaled and root planed root surfaces may accelerate bacterial invasion from treated root surfaces, the use of citric acid might be harmful in patients with inadequate plaque control.