According to a study by Rai et al. in 2008, they showed that “the levels of MMP-8, MMP-2 and MMP-9 were highly correlated to probing depth, and bleeding on probing and concluded that MMP-8, MMP-2 and MMP-9 are biomarkers of periodontal disease and aid in early detection of periodontitis or gingivitis [58].” This evidence concerns the gene MMP9 and gingivitis.