**5. Conclusions**

IL-17 plays an important role in inflammatory events that lead to the manifestation of psoriasis, rheumatoid arthritis, inflammatory bowel disease, and periodontitis. Although much remains to be clarified regarding its protective and pathologic functions, the current knowledge suggests its role as a potent proinflammatory mediator and bridge between innate and adaptive immune responses. Comorbid periodontitis is often observed in patients diagnosed with an immune-mediated inflammatory disease. Although a bidirectional causal relationship is ye<sup>t</sup> to be confirmed, regular screenings, preventive measures, and early treatment could reduce the burden of periodontitis in these patients, and vice versa. Many clinical randomized controlled trials prove the e fficacy of cytokine inhibitors that manipulate IL-17 and related pathways in the managemen<sup>t</sup> of psoriasis, rheumatoid arthritis, and inflammatory bowel disease. Unfortunately, reports regarding the therapeutic effects of cytokine inhibitors on gingival, periodontal, and oral mucocutaneous diseases are scant, which could be due to their restricted indication for severe systemic conditions, high costs, and adverse effects. However, further clinical research on the e ffects of biologics on gingival, periodontal, and oral tissues is needed to further elucidate the role of Th17-cells and the IL-23/IL-17 axis in the pathogenesis of periodontitis and its potential association with IMIDs.

**Author Contributions:** Conceptualization and resources, K.B. and T.B.; Investigation, K.B.; Writing—Original Draft Preparation, Review and Editing, K.B.; Writing—Review and Editing, T.B.

**Acknowledgments:** This research did not receive any specific gran<sup>t</sup> from funding agencies in the public, commercial, or not-for-profit sectors.

**Conflicts of Interest:** The authors declare no conflict of interest.
