Is apical periodontitis a matter of microbial diversity or time? A scoping review

The pathophysiology of apical periodontitis is complicated involving host immunological response, virulence factors, and a diverse microbiome. Understanding how microbial diversity influences lesion size is crucial for improving therapeutic strategies. This scoping review aimed to have an insight through literature to determine whether primary or secondary apical periodontitis lesions of different sizes are correlated with the quantity and diversity of microorganisms or the duration of the disease. The Joanna Briggs Institute (JBI) methodology for conducting scoping reviews was followed. A comprehensive electronic search was conducted through PubMed, Scopus, Web of Science, and Google Scholar to identify relevant studies published up to February 2025. In addition, handsearching was performed to identify additional studies that were not retrieved in the electronic search. Eligibility criteria of the screened papers included clinical studies performed in healthy patients with symptomatic or asymptomatic apical periodontitis where microbial analysis was performed. The EndNote Web reference manager (EndNote X9; Thomson Reuters) was used to ingest articles from various sources, categorize the references, and automatically eliminate duplicates. Out of 4010 papers, 132 studies met the inclusion requirements and were added to the current review. Approximately half of the papers examined bacterial diversity in endodontic infections, while just a small percentage discussed lesion size and were identified as randomized clinical trials. Brazil, USA, Germany and China were found to have the highest frequency of published articles. Fusobacteria, Streptococcus, Enterococcus faecalis and Porphyromonas species were the most detected microorganisms responsible for apical pathosis regardless of lesion size, while other microbiomes were associated with large lesions only, such as Olsenella, Lactococcus lactus and HHV-6 with 3% each and HPV with 6.1%. Other microbiomes such as Candida albicans, Filifactor alocis, HSV1, Pyramidobacter piscolens and Phocaeicola abscessus were seen only associated with small sized lesions with 4.3% each. Microbial diversity and microbial load seem to be a strong determinant of apical lesion size while lesion duration could not be adequately assessed due to cross-sectional study designs. Lesion size is an important variant to be recorded to give insight into microbial diversity and provide the basis for personalized targeted antimicrobial therapies in the future. This scoping review was registered in the open science framework; DOI: https://doi.org/10.17605/OSF.IO/DC95Z.