POSTN and periodontitis: In clinical studies investigating periostin levels in the gingival crevicular fluid (GCF) [75,76] and Pstn mRNA in tissues [77] at different stages of periodontal disease, it was shown that the total amount and concentration of periostin in the GCF, as well as Postn mRNA levels, are reduced with the progression and severity of the disease from healthy controls to chronic periodontitis groups and correlate negatively with clinical parameters of disease [77].