Variations in the susceptibilities of components of the endodontic microflora to biomechanical procedures.

The role of the endodontic microflora in pulpal disease and in endodontic treatment failures is well established. Thus the need for effective microbial control is one of the important justifications for biomechanical procedures. However the efficacy of this stage of treatment is dependent upon the vulnerability of the involved species, which may not be uniform. The aim of this study was to investigate variations in the susceptibilities of members of the root canal microflora to routine biomechanical procedures. Forty-two root canals were investigated microbiologically. Samples were collected before and after instrumentation and the bacterial findings were compared. In 15 cases of 'primary' root canal therapy, despite changes in the population size, no significant change in the species composition of the microflora was observed. However in 27 cases 'secondary' treatment, a decrease in the number of isolations of Peptostreptococcus spp. was found (P = 0.008). When all 42 cases were considered together, significant decreases were found between first and second samples for anaerobes (P = 0.0117) and for Grampositive species (P = 0.008), especially Peptostreptococcus spp. (P = 0.02). It was therefore concluded that certain species are more resistant to the biomechanical procedures than others.