Dark-field Observation of the Bacterial Distribution in Root Canals Following Pulp Necrosis

The purpose of this investigation was to study, by dark-field microscopy, the distribution of five types of bacteria in the coronal and apical thirds of root canals of teeth that had undergone pulpal necrosis. Twenty single-rooted teeth from 19 patients were sectioned after extraction into three equally long parts. Bacterial samples were taken from the apical and coronal thirds of the root canals and observed under a dark-field microscope. Data of bacterial counts were computerized and subjected to statistical correlation analysis. The results showed a significantly greater percentage of coccoids and rods in the coronal part than in the apical part. The percentage of motile rods did not differ in the coronal and the apical thirds. On the other hand, the percentage of filaments and spirochetes was slightly higher in the apical than in the coronal third, but showed no significant difference. A significant positive correlation was observed between the percentage of spirochetes in the apical third and the size of the radiographically visible lesion. The significance of these findings are discussed.