In 2009, Li et al demonstrated for the first time that moderate to severe chronic periodontitis was associated with an increased level of circulating endothelial progenitor cells (EPCs).22 In this systematic review, two RCTs demonstrated a significant decrease in the number of EPCs, notably CD31+, CD42–, and CD34+, three or six months after NSPT. The gene discussed is PECAM1; the disease is chronic periodontitis.