Abstract
Microorganisms in the complex root canal system and the extraradicular regions, including the periapical lesions and extraradicular biofilm may cause root canal treatment failures. However, few studies described the difference between the intraradicular and extraradicular infections from the same tooth associated with persistent apical periodontitis. This study aimed to characterize the microbiome present in the root canal, extraradicular biofilm, and periapical lesions associated with persistent apical periodontitis. The microbial communities in the root canal, extraradicular biofilm, and periapical lesions were investigated by Illumina high-throughput sequencing using Illumina Hiseq 2500 platform. The dominant phyla in the extraradicular and intraradicular infections associated with persistent apical periodontitis were Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria, and the genera Fusobacterium, Morganella, Porphyromonas, Streptococcus, and Bifidobacterium dominated across all samples. Although extraradicular infection sites showed higher OTU richness and β-diversity compared to intraradicular samples, the occurrence of sinus tract rather than the sampling sites demarcated the microbial communities in the infections associated with persistent apical periodontitis. PERMANOVA analysis confirmed that the samples with or without sinus tracts contained significantly different microbial communities. Porphyromonas, Eubacterium, Treponema, and Phocaeicola were found in significantly higher levels with sinus tracts, whilst Microbacterium and Enterococcus were more abundant in samples without sinus tracts. In conclusion, diverse bacteria were detected in both intraradicular and extraradicular infections associated with persistent apical periodontitis, which might be influenced by the occurrence of the sinus tract. The results may provide new insight into the pathogenesis of persistent apical periodontitis.
Highlights
Persistent apical periodontitis has been reported to occur in 1020% of teeth, even when the root canals are thoroughly prepared, disinfected, and obturated, leading to periapical lesions persist after the failure of endodontic treatment and retreatment (Nair, 2004)
To investigate the microbial communities associated with persistent apical periodontitis, microbial samples from root canal, extraradicular biofilm and periapical lesions from patients with persistent apical periodontitis were investigated by 16S rRNA gene high-throughput sequencing
The number of total OTUs detected in both the extraradicular biofilm and periapical lesions were higher than the root canal filling samples (i.e., 1069 OTUs and 971 OTUs vs. 683 OTUs), which indicated the microbial compositions in the extraradicular infection sites were more variable than the intraradicular infection site (Figure 2A)
Summary
Persistent apical periodontitis has been reported to occur in 1020% of teeth, even when the root canals are thoroughly prepared, disinfected, and obturated, leading to periapical lesions persist after the failure of endodontic treatment and retreatment (Nair, 2004). Residual bacterial biofilm located in the complex apical root canal system and extraradicular regions was considered to be an important factor affecting the persistent apical infections (Zakaria et al, 2015; Bronzato et al, 2021). By using transmission electron microscopy, complex multispecies biofilm was present in root canals of persistent apical periodontitis (Carr et al, 2009). Extraradicular biofilm was observed on the surface of cementum from root tip to coronal (Wang et al, 2012), and was detected in 80-100% of root canal treatments considered endodontic failure (de Sousa et al, 2017). The intraradicular and extraradicular regions in the core apical area play an essential role in the persistent chronic inflammatory process
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