Introduction: Apical periodontitis is a sequela of endodontic infection, which manifests as a host defense response to the microbial challenge emanating from the root canals. To achieve an optimal outcome, microorganisms must be eliminated or reduced to levels that allow healing of the periradicular tissue. Objective: To analyze the literature on microorganisms, such as Enterococcus faecalis, Fusobacterium nucleatum, Candida albicans, Epstein-Barr, which are important in persistent apical periodontitis. Methodology: Articles on the subject published through PubMed, SCOPUS and Google Scholar databases were analyzed, with emphasis on the last 5 years. It was performed with the words "Enterococcus faecalis", "Fusobacterium nucleatum", "Candida albicans", "Epstein-Barr", "Herpesviridae", "Root canals", "Persistent apical periodontitis". Results: E. faecalis involved in persistent apical periodontitis because of its adaptability to extreme environments, growing in alkaline pH and using periodontal ligament fluids as nutrients. Lysed Fusobacterium nucleatum cells could potentially increase the severity of persistent apical periodontitis. Candida albicans is one of the dominant pathogens in persistent apical periodontitis because of its membrane protein Msb2. Epistein-Barr virus may be implicated in the pathogenesis of apical periodontitis by direct cytopathic action on infected cells, however, its replication in persistent apical periodontitis is still unclear. Conclusions: The microbiota of teeth with persistent apical periodontitis, presents a mixed and complex profile, it is important to know the role of these microorganisms, because microbial persistence, seems to be the most important factor in root canal treatment failure.

Introduction: Filifactor alocis is considered an emerging pathogen in various oral infections, mainly endodontic. Objective: To analyze the literature on the bacterium Filifactor alocis, including its virulence factors, nutrition, diagnosis, epidemiology, and treatment. Methodology: Articles on the subject published through the PubMed, SCOPUS and Google Academic databases were analyzed, with an emphasis on the last 5 years. It was carried out with the words "Filifactor alocis", "Gram-positive", "Anaerobic bacteria", "Endodontic infections". Results: 3-methyldenine DNA glycosylase, its ability to encode FtxA exotoxin, and its high ability to form hydrogen sulfide from L-cysteine are some of its virulence factors. 16S rRNA gene sequencing is the most common detection method. The relatively high detection of F. alocis associated with infections of endodontic origin, makes it a potential putative endodontic pathogen. Correct chemical-mechanical instrumentation and a hermetic seal is the best treatment to eradicate Filifactor alocis. Conclusions: Filifactor alocis is one of the most frequent bacteria in various endodontic infections. Therefore, its eradication is crucial to achieve the elimination of the infection.