The ROC and AUC analysis for MMP-8, MMP-9 and TIMP-1 showed interesting findings: although only MMP-9, as a single biomarker, appeared able to discriminate (only) between health and periodontitis groups (Fig. 2C, Table 4), various combinations of these three biomarkers proved able to effectively discriminate: (i) between all three group comparisons, through the MMP-9/TIMP-1 and the (MMP-8 + MMP-9)/TIMP-1 ratios; and (ii) between health vs periodontitis and gingivitis vs periodontitis groups through the MMP-8/TIMP-1 ratio and the MMP-8 + MMP-9 sum. The gene discussed is MMP9; the disease is gingivitis.