IL17A and periodontitis: Many studies have proven gene polymorphisms in cytokines such as IL‐1α (12–28), IL-1β (12, 16, 18, 24, 29–55), IL-2 (56–60), IL-4 (61–73), IL‐6 (74–86), IL-23 (87), IL-10 (16, 42, 84–86, 88–110), IL-13 (66, 111, 112), IL-17 (60, 73, 87, 113–117), TNF-α (16, 35, 38, 44, 48, 85, 118–132), IFN (70, 85, 102, 133–136), and TGF (42, 137–143), which often play various vital roles in periodontitis immune pathogenesis or in the prevention of periodontitis immune responses.