Post‐Treatment Apical Periodontitis: Endodontic Infection Contributes to Circulating Microbial <scp>DNA</scp>

This study investigated the impact of post-treatment apical periodontitis on microbial DNA in patients' blood circulation. Samples from the root apex, periapical lesion and peripheral blood of 11 patients, along with peripheral blood from nine healthy controls, were analysed using next-generation sequencing. The microbial DNA composition, diversity and linear discriminant analysis effect size were analysed. The SourceTracker was applied to trace microorganisms of peripheral blood. Proteobacteria dominated peripheral blood and periapical lesions, while Actinobacteria prevailed in the root apex. Patients exhibited higher microbial diversity in blood but reduced α-diversity in the root apex compared to other sites. Moreover, Bacteroides, as well as Aliihoeflea, Oceanicaulis, Comamonas, Shigella and Acinetobacter, showed increased relative abundance in the blood of patients. Additionally, the root apex contributed 26% and the periapical lesion contributed 76% to peripheral blood for the bacteria. These findings suggested unique microbial translocation in post-treatment apical periodontitis patients.