MMP9 and periodontal disorder: Patients with untreated periodontal disease had significantly higher levels of salivary MMP-9 compared to controls (control group: 155.6 ± 38.63 ng/mL; PD: 582.27 ± 48.2 ng/mL; POD group: 602.55 ± 64.55 ng/mL; p < 0.0001 for both, Figure 1).