NOS2 and periodontitis: The calcium-deficient prooxidant model of chronic generalized periodontitis (CGP) leads to a typical clinical picture of periodontitis—hyperemia, edema, the formation of periodontal pockets, bleeding, tooth mobility, and an increase in molecular–biochemical markers of nitrosative stress in the blood, such as iNOS, NOx, and nitrotyrosine, accompanied by a decrease in glutathione levels and the expression of glutathione peroxidase-4 and Zn/Cu-dependent superoxide dismutase.