Establishment of diagnosis of apical periodontitis utilizing the microbiological and immunological profiling of root canals

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This study aimed to profile microflora of root canals before and after root canal therapy, utilizing real-time PCR and cloning-sequence analyses based on 16S rRNA genes. Informed consent was obtained from 5 patients, and 6 single-rooted teeth with periapical lesions were investigated. Upon access opening, dentin sample was collected from the root canal. When the periapical lesion healed clinically through chemo-mechanical cleaning and intracanal medication, the canal dentin was sampled again. The quantification of total bacteria was performed by real-time PCR using universal primers based on 16S rRNA genes. PCR products were cloned and partially sequenced, and bacterial identification was carried out by comparative analysis with the GenBank database. The concentrations of bacterial DNA were 0.36-152.0 (52.7±54.1) ng/mL upon access opening, and lowered to 0.02-36.00 (10.9±16.6) ng/mL after root canal therapy. The cloning-sequence analysis revealed that although Fusobacterium were initially predominant, Pseudomonas, Bradyrhizobium and Methylobacterium prevailed after root canal therapy. These results suggested that changes in bacterial flora brought by root canal therapy were not only in its quantity but also in quality, and that the dramatic shift in its components might also contribute to the healing process.