Root canal microbiota in diabetic versus non-diabetic patients with apical periodontitis: A systematic review

Background This systematic review aimed to evaluate the differences in root canal microbiota composition and microbial load between diabetic and non-diabetic individuals with apical periodontitis. Methods Electronic searches were conducted in PubMed/MEDLINE, Scopus, Web of Science, Google Scholar, the Cochrane Library and EBSCO up to 9 April 2026.Clinical studies using culture-dependent or molecular methods to identify microbial taxa in infected root canals of diabetic and non-diabetic individuals were included. Data on diabetes status, infection type, microbiological method, identified taxa, and quantitative microbial outcomes were extracted. Methodological quality was assessed using the Joanna Briggs Institute critical appraisal tool. Results Sixteen studies were included. Most used molecular methods, while few used culture or combined culture/molecular approaches. The studies varied in infection type, microbiological method, glycemic status reporting, and outcome metrics. Several studies reported differences in the prevalence or relative abundance of selected bacterial taxa in diabetic patients, including Peptostreptococcus spp., Porphyromonas gingivalis , Eubacterium infirmum, Enterococcus faecalis, Olsenella, Pseudoramibacter, and Fannyhessea . Fungal and archaeal findings were also reported in a limited number of studies. However, quantitative microbial findings could not be directly compared because different measures were used, including CFU counts, PCR-based detection, qPCR-derived bacterial counts, and sequencing-based relative abundance data. Conclusion Diabetes mellitus may be associated with differences in the reported endodontic microbial profile of teeth with apical periodontitis. However, the evidence is observational, clinically heterogeneous, and limited by small sample sizes, inconsistent glycemic reporting, and inadequate control of confounding factors.