Purpose of Review <p>Oral health problems can aggravate the course of systemic diseases, as well as systemic diseases or accompanying therapies may manifest in the oral cavity. We conducted a literature review to discuss the bidirectional relationship between periodontal disease and thyroid diseases.</p> Recent Findings <p>Many proinflammatory cytokines, present in thyroid follicular cells, are linked to the pathophysiology of periodontitis. Systemic autoimmune reactions, also in autoimmune thyroid diseases, may be triggered by oral dysbiosis associated with the advancement of periodontal disease. Moreover, patients with thyroid diseases demonstrated significantly worse periodontal health to those with no systemic health issues. About 5% of periodontitis patients reported the concomitance of thyroid diseases. Interestingly, non-surgical treatment of periodontal disease can improve patients’ thyroid parameters.</p> Summary <p>The relationship between periodontitis and thyroid diseases seems to be bidirectional. However, further research is needed to confirm these findings and understand in more detail this relationship to achieve better treatment of these diseases.</p>