TNFRSF11B and periodontitis: As for OPG polymorphisms, studies have reported higher levels of OPG in the gingival crevicular fluid, saliva, and gingival tissues of healthy individuals than in patients with periodontitis [64–66], and Mogi et al. [66] observed higher levels of OPG in the gingival crevicular fluid in mild periodontitis compared to the moderate or severe forms.