On the other hand, Daghigh, et al. 27, found that nitric oxide and iNOS concentrations are higher in fibroblasts from gingival tissue in patients with periodontitis than in cells of healthy subjects 27, and Sun, et al. 28, described higher iNOS levels in gingival tissue in rats with periodontitis than in the control group. This evidence concerns the gene NOS2 and periodontitis.