In the paper that compared cytokine levels for 54 periodontitis patients and 40 healthy controls, cytokines IL‐1β, IL‐4, IL‐6, IL‐10, IL‐17A, IL‐17F, IL‐21, IL‐22, IL‐23, IL‐25, IL‐31, IL‐33, IFN‐γ, sCD40L and TNF‐α were measured in saliva and serum at baseline, 3, 6 and 12 months after treatment. Here, IL31 is linked to periodontitis.