The oral microbiome, the second largest and most diverse microbial community in the human body, is essential for maintaining oral and systemic health. Under homeostatic conditions (eubiosis), commensal microorganisms support immune regulation, metabolic processes, and colonization resistance. Disruption of this balance (dysbiosis) leads to ecological and functional shifts in the subgingival biofilm, favouring pathogenic species.

The polymicrobial synergy and dysbiosis model emphasizes that periodontitis is not caused by a single pathogen but results from cooperative and competitive microbial interactions that amplify pathogenicity. Tissue breakdown is primarily mediated by the host’s dysregulated immune-inflammatory response rather than direct microbial action. Advances in diagnostic approaches, including 16S rRNA sequencing, metagenomics, and biomarker analysis in gingival crevicular fluid and saliva, provide valuable insights into microbial ecology and disease activity.