MMP9 and periodontal disorder: Additionally, interferon (IFN)-γ, MMP-9, MMP-12, receptor activator of the nuclear factor-Κb ligand (RANKL), osteoprotegerin (OPG), alkaline phosphatase (ALP), cathepsin B, hemoglobin, salivary neuropeptides, and oxidative stress-related and terminal glycation end products are also being investigated as biomarkers of periodontal disease, although their usefulness is uncertain [36].