Systemic immune inflammation index in patients with recurrent aphthous stomatitis

•RAS is a chronic, idiopathic, ulcerative oral mucosal disease.•SII is a new and inexpensive biomarker that can easily be calculated using the platelet, neutrophil, and lymphocyte count.•SII may be a valuable marker to demonstrate the role of systemic inflammation in RAS etiopathogenesis.•Vascular, thrombotic, and inflammatory processes are thought to have a role in RAS activation.