IL17A and periodontitis: Periodontitis is characterized by a chronic inflammation caused by oral bacteria and leucocyte infiltration with progressive destruction of the alveolar bone and it seems to share the same pathogenetic mechanisms with RA: accumulation of leucocyte infiltration, release of inflammatory cytokines, and mediators such as prostaglandin E2 (PGE2), tumour necrosis factor (TNF)-α, and several other citokines, such as interleukin (IL)-1b, IL-6, IL-17, IL-33, IL-12, IL-18r [33].