TNFSF11 and periodontitis: It has been shown that RANKL is upregulated, whereas osteoprotegerin (OPG) is downregulated in periodontitis, compared to periodontal health, resulting in an increased RANKL/OPG ratio, leading to the destruction of the connective tissue attachment and alveolar bone loss and, consequently, the migration of the junctional epithelium apically [37,38,39,40,41].