CDK9 and periodontal disorder: To further investigate their role in the periodontal inflammation, we also conducted immunohistochemical staining, finding that increased expression of the three proteins in both the gingival epithelium and subepithelial connective tissue in the inflamed gingiva, further indicating that TOP1, Brd4 and CDK9 participated in the progression of periodontal diseases (Fig. 1C).