AP: Apical periodontitis, CP: chronic periodontitis, sTNF-α: Serum tumor necrosis factor-alpha, sIL-10: Serum interleukin-10, sNO: Serum nitric oxide, sPGE2: Serum prostaglandin E2, GCF: Gingival crevicular fluid. The gene discussed is TNF; the disease is periapical periodontitis.