Objective: To investigate the morphology,distribution and relative position of the bacteria in infected root canals with chronic apical periodontitis and make some clinical inferences.
Methods: Seven extracted roots with chronic apical periodontitis were collected. Immediately after extraction, all specimens were rinsed in sterile saline solution. The remaining tooth crowns were cut off with carborundum disks under water spray. Longitudinal grooves following the root length axis were cut along the entire root by using tapered diamond burs under water spray, and the roots were then split with a chisel into two halves. One half of the roots were decalcified, and after dehydration and embedding in paraffin, serial sections of 4 μm were cut, parallel to the long axis of the roots. The sections were stained using the Brown & Brenn methods, which were examined with a light-transmitting microscope for the distribution of bacteria in the root canals. The other half of the roots were dehydrated, sputtered coated with gold, and then examined for the occurrence of bacteria in the root canals using a scanning electron microscope.
Results: Histobacteriologic observation showed that bacteria were found in all the seven specimens, which were clogged with a dense bacterial biofilm in the apical third of the main canal. Bacteria could penetrate into the dentinal tubules about 140-1 000 μm. Scanning electron microscopy observation showed that bacteria consisting of cocci, rods and/or filaments with amorphous materials formed the typical biofilm structure in the apical third of the root canals.
Conclusion: The findings support the view that bacteria colonizing the root canal system play an essential role in the pathogenesis of periradicular diseases. In all the seven specimens, bacteria usually formed dense aggregates on the root canal walls, penetrating the dentinal tubules in the apical third of the main canal. Dense bacteria and amorphous materials filled the inter-bacterial spaces and formed the typical biofilm structure.