Predominant obligate anaerobes invading the deep layers of root canal dentin

This study was carried out to investigate the presence and types of bacteria invading the deep layers (0.5-2.0 mm from the surface of the root canal wall) of infected dentine of human root canals by sampling with an anaerobic glove box system the split surfaces of eight freshly extracted teeth. More bacteria were recovered after incubation in an anaerobic glove box than after aerobic incubation in air with 30 per cent CO2. Out of 256 predominant bacterial isolated, 205 isolates (80 per cent) were obligate anaerobes. These findings suggest that the environment of deep layers of endodontic dentinal lesions is anaerobic and favours the growth of anaerobes. Among the obligate anaerobic isolates, strains belonging to Lactobacillus (30 per cent) and Streptococcus (13 per cent) were predominant, followed by Propionibacterium (9 per cent). No strains of obligate anaerobic Gram-negative rods were isolated. The microflora of deep layers of infected root dentine is somewhat similar to that of the deep layers of carious lesions in coronal dentine.