J-shaped association between systemic immune-inflammation index and periodontitis: Results from NHANES 2009-2014.

Background: To examine the relationship between the systemic immune-inflammation index (SII) and periodontitis and to investigate possible effect modifiers.

Methods: Data used in the present cross-sectional study are from the National Health and Nutrition Examination Survey (NHANES) 2009-2014 (N = 10,301). The SII was calculated using the following formula: (neutrophils count × platelet count)/lymphocytes count. The category of periodontitis was defined by the Centers for Disease Control and Prevention and American Academy of Periodontology (CDC/AAP) classification. We employed natural cubic spline and multivariable logistic regression analyses to evaluate the associations of the SII with periodontitis.

Results: The associations between SII and periodontal health followed a J-shape (p < 0.001). The risk of periodontitis tended to reduce with the increment of log(SII) in participants with log(SII) ≤ 8.66 (odds radio [OR] = 0.83; 95% CI: 0.69-0.999), especially among non-Hispanic Whites (OR = 0.70; 95% CI: 0.52-0.95), and increased with the increment of log(SII) in participants with log(SII) > 8.66 (OR = 1.19; 95% CI: 1.02-1.38). A similar trend was also observed between the SII and the number of sites with probing pocket depth (PPD) ≥4 mm and clinical attachment loss (CAL) ≥ 3 or 5 mm. Furthermore, we found a significantly stronger correlation between lymphocytes and either neutrophils or platelets in individuals with log(SII) > 8.66, as opposed to those with log(SII) ≤ 8.66.

Conclusions: There is a J-shaped association between SII and periodontitis in US adults, with an inflection point of log(SII) at 8.66, which may provide potential adjunctive treatment strategies for periodontitis with different immune response states. Further prospective trials are still required to confirm our findings.