In the subgroup analyses, a significantly increased risk of the association between the COX2 -765G/C variants and periodontitis was found in studies with population-based controls (C vs. G, ORs = 1.81, CI = 1.22–2.71; CC vs. GG, ORs = 4.47, CI = 1.25–15.95; CC vs. GG + GC, ORs = 4.47, CI = 1.21–16.44; CC + GC vs. GG, ORs = 1.52, CI = 1.24–1.86), while a significantly decreased risk was found in studies that with hospital-based controls (C vs. G, ORs = 0.33, CI = 0.12–0.95; CC + GC vs. GG, ORs = 0.28, CI = 0.09–0.88) (Table 2 and Fig. 2). The gene discussed is PTGS2; the disease is periodontitis.