Correlation between systemic immune-inflammatory index and graded diagnosis of periodontitis: a combined cross-sectional and retrospective study

To investigate the association between periodontitis and inflammatory biomarkers, including systemic immune-inflammatory index (SII), neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio, and lymphocyte-to-monocyte ratio. Our study comprised a cross-sectional analysis (an indirect evidence group and a periodontal health control group from January to October 2023) and a retrospective study (a direct evidence group and a non-maintenance group from January 2014 to March 2022). We analyzed demographic data, imaging measurements, and peripheral blood counts. The study included 131 participants in the indirect evidence group, 132 in the healthy control group, 123 in the direct evidence group, and 76 in the non-maintenance group. The indirect evidence group exhibited significantly altered inflammatory biomarker levels compared to the healthy controls. Receiver operating characteristic curve analysis indicated that SII was the most effective biomarker for diagnosing periodontitis, with an area under the curve 0.758 and a Youden index 0.409. The optimal cut-off value was 437.07 × 10⁹/L, achieving a sensitivity 46.2% and a specificity 94.7%. Correlation analyses revealed significant associations between the biomarker levels and periodontitis grades, with SII showing the highest correlation coefficient (0.942). In the direct evidence group, supportive periodontal therapy significantly mitigated changes in these biomarkers. An SII level exceeding 437.07 × 10 /L could facilitate the periodontitis diagnosis and disease grade determination. SII can be utilized to assess and monitor periodontitis severity and treatment response.