The Role of Neutrophil Extracellular Traps in Periodontitis Pathogenesis: A Systematic Review of <i>Ex Vivo</i> Studies

Objectives: Neutrophil extracellular traps (NETs) have emerged as critical effectors in immune defense but also as potential drivers of tissue damage in chronic inflammatory diseases. Their role in periodontitis, a highly prevalent condition characterized by dysregulated host–microbe interactions, remains incompletely defined. This systematic review aimed to synthesize, for the first time, ex vivo human evidence on the presence, activity, and clinical significance of NETs in periodontitis. Methods: A comprehensive search of Medline, Web of Science, and Scopus was conducted up to August 2025. Eligible studies included ex vivo human investigations assessing NETs or NET markers in gingival tissues, gingival crevicular fluid, saliva, blood, or biofilms from patients with periodontitis. Study selection, data extraction, and risk-of-bias assessment were conducted in duplicate, and the protocol was registered in PROSPERO (CRD420251109174). Results: Seventeen studies met the inclusion criteria. NET markers such as citrullinated histone H3 (CitH3), myeloperoxidase (MPO), and neutrophil elastase were consistently elevated in periodontitis samples compared with controls. Several studies reported a reduction in NET levels or improved NET degradation following periodontal therapy. NETs were also implicated in biofilm stability and in systemic associations with rheumatoid arthritis and chronic kidney disease. However, heterogeneity in methodologies, small sample sizes, and inconsistent marker use limited comparability across studies. Conclusions: Ex vivo evidence indicates that aberrant NET formation and impaired clearance contribute to periodontal inflammation and tissue destruction. Nonetheless, methodological variability and risk of bias constrain definitive conclusions. Standardization of detection methods, consensus on marker panels, and exploration of neutrophil subsets and systemic confounders are essential to establish NETs as reliable biomarkers and therapeutic targets in periodontitis.