Systemic immune‐inflammation index and its role in the relationship between subgingival microbiota and periodontal inflammation

BACKGROUND: To investigate whether the subgingival microbiota or the systemic immune-inflammation index (SII) is more closely associated with the periodontal inflamed surface area (PISA). METHODS: Ninety participants were enrolled in this cross-sectional study for subgingival microbiota sequencing, SII, and PISA assessment. Restricted cubic spline and regression analyses examined the SII-PISA relationship. Microbiota analyses (LEfSe, alpha-diversity, partitioning around medoids clustering) and interaction analyses were used to evaluate whether microbiota-SII interactions were associated with PISA. RESULTS: SII ≤ 9.13), increased PISA was linked to greater microbial richness (P = 0.031) and a Porphyromonas-dominant microbial type. Stratified and interaction analyses provided additional support for these findings. CONCLUSION: At low SII levels, the periodontitis severity showed significant associations with microbial dysbiosis-related features, whereas at higher SII levels, it was closely related to systemic immune cell imbalance, indicating that immune-inflammatory modulation may be particularly important for patients with a high SII level. PLAIN LANGUAGE SUMMARY: This study explored the links between a person's immune cell imbalance (assessed by the systemic immune-inflammation index, SII), subgingival microbiota, and periodontitis severity. Ninety participants were tested for their blood cell markers of inflammation and the composition of microbiota. A nonlinear relationship between the SII and the periodontal inflamed surface area (PISA) was observed. There was a turning point: when SII was low, periodontitis severity was strongly linked to an imbalanced subgingival microbiota. However, when SII was high, periodontitis severity was more strongly related to an imbalance in immune cells. These findings indicate heterogeneity in the association among SII, oral microbiota, and periodontal inflammation.