S100A9 and periodontitis: Epidemiologic evidence has linked both; however, the change of markers in gingival crevicular fluid has been poorly evaluated.<h4>Objective</h4>To evaluate the levels of IL-17A, IL-22, IL-23, S100A7, S100A8, and S100A9 in gingival crevicular fluid of psoriatic and healthy subjects with and without periodontitis and their relations to psoriasis severity.<h4>Methods</h4>Cross-sectional study.