Fifty‐six C57/BL6J mice were randomly allocated to seven experimental groups: (a) control group (P–Pso–) with no treatment; (b) periodontitis (P+Pso–) with periodontal therapy; (c) periodontitis (P+Pso–) with TNF‐α inhibitor; (d) psoriasis (P–Pso+) with TNF‐α inhibitor; (e) periodontitis and psoriasis (P+Pso+) with periodontal therapy; (f) P+Pso+ with TNF‐α inhibitor; and (g) P+Pso+ with both periodontal therapy and TNF‐α inhibitor. This evidence concerns the gene TNF and periodontitis.