Background Persistent/secondary infections of human root canals play an important role in the failure of endodontic treatment. This study used 16S rRNA sequencing to assess microbial diversity in root-filled teeth associated with failed endodontic treatment. Methods DNA was extracted from 15 teeth with persistent intraradicular infections, and the 16S rRNA of all present bacteria were amplified by PCR, followed by cloning and sequencing of the 16S rRNA amplicons. Results All sample extracts were positive for PCR amplification using the universal 16S rRNA gene primers. Negative control reactions yielded no amplicons. Sixty-five phylotypes belonging to seven phyla were identified from 760 clones; a mean of 9.4 phylotypes were detected in each sample （range 3-15）. Twenty-eight phylotypes were detected in more than one sample, revealing a high inter-sample variability. Parvimonas micra （60%, 9/15）, Solobacterium moore （47%, 7/15）, Dialister invisus （33%, 5/15）, Enterococcus faecalis （33%, 5/15）, Filifactor alocis （27%, 4/15）, and Fusobacterium nucleatum （27%, 4/15） were the prevalent species. Nineteen as-yet-uncultivated phylotypes were identified, comprising a substantial proportion of the bacteria in many cases. Conclusions Persistent intraradicular infections were present in all root-filled teeth associated with failed endodontic treatment. The current observations reveal new candidate endodontic pathogens, including as-yet-uncultivated bacteria and phylotypes that may participate in the mixed infections associated with post-treatment apical periodontitis.
目的评价4种根管充填方法的根充同质性和致密度，以期为临床应用提供参考。方法选择40颗单根管牙，镍钛旋转器械进行冠向下法根管预备，按随机数字表法分4组，分别采用热牙胶垂直加压充填法（A组）、固体核心载体充填法（B组）、常温流动牙胶充填法（C组）和冷牙胶侧压充填法（D组）进行根管充填，每组10颗牙。分别对每颗牙在4个水平进行片切，体式显微镜拍照，进行图像分析并计算牙胶充填面积百分比（percentage of gutta-percha filled area，PGFA），比较各组整体及根尖、根中、根冠区不同部分的根充同质性和致密度。结果根管整体水平A、B、C、D组PGFA值分别为（96．5±3．6）％、（95．6±3．9）％、（86．5±5．7）％、（81．5±4．2）％；根尖区各组PGFA值分别为（96．8±3．8）％、（97．2±4．0）％、（89．4±5．1）％、（79．84-3．4）％；根中区各组PGFA值分别为（95．6±4．0）％、（95．64-3．9）％、（83．4±5．3）％、（80．6±3．6）％；根管整体水平、根尖和根中区均显示A组和B组显著优于c组和D组（P〈0．01），D组显著低于其他各组（P〈0．01）；根冠区A组显著高于其他三组（P〈0．01），B组显著低于A组（P〈0．01），但显著高于C和D组（P〈0．01），C、D组之间差异无统计学意义（P〉0．05）。结论热牙胶垂直加压充填技术和固体核心载体充填技术在整体和根管各个部位均显示出较好的同质性和致密度；冷牙胶侧压组充填同质性和致密度欠佳。
