IL6 and periodontitis: In the periodontitis group, nine studies showed all of the cytokines were elevated in periodontitis compared to the controls; six studies showed no difference between the controls and periodontitis, and one study only reported elevated IL-6 in severe periodontitis compared to the mild periodontitis group (Figure 3a) [21,22,23,24,25,26,27,28,29,30,31,32,33].