Background & Objective: Type 2 diabetes mellitus (T2DM) and periodontitis share a well-established bidirectional relationship, where systemic inflammation act as a critical mechanistic link. Omentin-1, an anti-inflammatory adipokine with potential metabolic regulatory functions, and C-reactive protein (CRP), a widely recognized marker of systemic inflammation, may play opposing but interconnected roles in this association. This cross-sectional study aimed to evaluate salivary levels of Omentin-1 and CRP in T2DM patients, at varying stages of periodontitis, in comparison with healthy controls.
 Materials & Methods: In this cross-sectional study, 160 participants were enrolled, including 32 healthy controls and 128 T2DM patients stratified into four equal groups based on periodontitis stages I–IV. Unstimulated saliva samples were collected, and periodontal parameters—probing pocket depth, clinical attachment level (CAL), and bleeding on probing (BOP)—were recorded. Salivary levels of Omentin-1 and CRP were measured using ELISA.
Results:  Omentin-1 levels were significantly higher in healthy controls (210.61 pg/mL) than in T2DM-periodontitis patients (P < 0.001), showing a progressive decline with advancing periodontitis stages (Stage I: 180.72; Stage II: 153.16; Stage III: 123.90; and Stage IV: 122.82 pg/mL). Conversely, CRP levels were significantly elevated in T2DM-periodontitis patients (P < 0.001), increasing with disease severity (Stage I: 120.4; Stage II: 178.0; Stage III: 289.4; and Stage IV: 501.0 pg/mL) compared to controls (45.3 pg/mL).
Conclusion:  Salivary Omentin-1 levels decrease with the progression of periodontitis in T2DM patients while CRP levels increase, suggesting a potential protective role of Omentin-1 against inflammation. These biomarkers may serve as useful indicators for monitoring both periodontitis severity and metabolic dysfunction in T2DM, underscoring their clinical relevance.