To compare the intraradicular bacterial community structures in under-filling teeth with or withoutperiapical infection.

The intraradicularbiofilm samples were collected from under-filling teeth with periapicalinfection (apical periodontitis group, 3 teeth) and underfilling teeth withoutperiapical infection (non-apical periodontitis group, 2 teeth). The V3, V6 hypervariable regions of bacterial 16S rRNA genes were amplified, and the high-throughput sequencingwasperformed. Thecomposition and structure characteristic of intraradicular microbiota were revealed by bioinformatics analysis.

The microbiotain apical periodontitis group comprised of Firmicutes, Proteobacteria, Actinobacteriad and others, total 22 phyla. While the microbiotain non-apical periodontitis group comprised of Firmicutes, Proteobacteria, Actinobacteria and others, total 8 phyla. The complexity of the microbiotain apical periodontitis groupwas significantly higher than without apical periodontitis group, but both groups comprised thesimilar most representivephyla.

The diversity of intraradicular bacterial community in underfillingteeth with apical periodontitis was higher than those in non-apical periodontitis.