Background: According to the 2017 classification of periodontal and peri-implant diseases, Stage III and IV periodontitis are defined as severe and advanced forms, respectively. However, current diagnostic differentiation relies largely on clinical probing and lacks objective biomarkers that reflect the systemic inflammatory burden. The Systemic Immune-Inflammation Index (SII)—integrating neutrophil, lymphocyte, and platelet counts—comprehensively reflects the balance of the host “inflammation-immunity-thrombosis” network. Previous studies, however, often failed to adequately control for systemic confounders such as age, smoking status, and metabolic syndrome. Therefore, this study aims to apply Propensity Score Matching (PSM) to rigorously adjust for confounding variables and to evaluate the clinical utility of SII as a novel biomarker for differentiating Stage IV from Stage III periodontitis. Methods: This retrospective case-control study enrolled patients diagnosed with Stage III and IV periodontitis. To mitigate selection bias, a 1:1 PSM analysis was performed to balance baseline covariates, including age, gender, smoking status, diabetes mellitus, hypertension, body mass index (BMI), and educational level. Differences in SII levels between groups were analyzed using the Mann-Whitney U test. A multivariate logistic regression model was constructed to assess the association between SII and the risk of Stage IV periodontitis. Additionally, Restricted Cubic Spline (RCS) modeling was employed to explore potential non-linear dose-response relationships. Results: After PSM, a total of 212 patients with balanced baseline characteristics were included (106 each for Stage III and IV). Analysis revealed that SII levels were significantly higher in patients with Stage IV periodontitis compared to those with Stage III Median: 577.23 vs. 529.06, p = 0.003. Multivariate logistic regression confirmed that, even after adjusting for all confounding factors, elevated SII levels remained an independent risk factor for progression to Stage IV periodontitis (p poverall = 0.009), with no evidence of a non-linear threshold effect (pnon-linearity = 0.069). Conclusion: Even after rigorous adjustment for systemic confounders, elevated SII levels are significantly associated with Stage IV periodontitis and exhibit a linear cumulative trend. As a cost-effective and accessible objective indicator, SII not only aids in the precise grading of Stage III and Stage IV periodontitis but also highlights the heightened systemic inflammatory burden in severe cases, thereby supporting the implementation of multidisciplinary management strategies.
Wu et al. (Thu,) studied this question.