For the PubMed library, the search terms were as follows: (periodontal disease [MeSH Terms]) OR periodontitis [MeSH] Terms]) OR gingivitis [Title/Abstract]) OR inflammatory biomarkers [Title/Abstract]) OR gingival crevicular fluid [Title/Abstract]) OR GCF [Title/Abstract]) OR rheumatoid arthritis [Title/Abstract]) OR fractalkine [Title/Abstract]) OR CX3CL1 [Title/Abstract]) AND (cytokines [MeSH Terms]) OR chemokines [Title/Abstract]) OR cytokines [Title/Abstract]). Here, CX3CL1 is linked to periodontal disorder.