Survival against the odds: microbiology of root canals associated with posttreatment disease

Most periapical lesions resolve after root canal treatment of teeth with primary infections. Over the last decade there has been a renewed focus on post-treatment apical periodontitis and its etiology. This review describes the microbiota associated with persistent post-treatment infection, including microbial identification, ecology, and environmental selection. Compared with untreated teeth, the infection pattern in root canals with post-treatment disease shifts to a resistant, mainly Gram-positive community. The main challenge in root canal re-treatment is access to the residual apical infection. Elimination of the microbial flora, or a dramatic reduction and sufficient ecological shift to allow host tissue healing, remains the biological goal.