Mahmood, Y. G. ., V. M. . Hussein, and A. H. . Aziz. “The Relationship Between Serum Vitamin D Level & Chronic Periodontitis in Patients Attending Khanzad Center in Erbil City”. AMJ (Advanced Medical Journal) , vol. 5, no. 2, June 2023, pp. 99-104, doi:10.56056/amj.2019.109.