MMP9 and periodontitis: A study reported that patients with both chronic periodontitis and diabetes had much higher levels of MMP-8 and MMP-9 in periodontal tissue compared to patients with chronic periodontitis but systemically healthy patients and healthy controls (Kumar et al., 2006), and there was a trend toward significantly increased MMP-8 in patients transitioning from the absence of both diseases (Hardy et al., 2012).