S. . . D. Jassim and L. . . M. Ibrahim, “Correlation between Periodontal Health Status and Salivary Matrix Metalloproteinase-9 Levels in Smoker and Non-Smoker Chronic Periodontitis Patients (A Comparative Study) ”, J Bagh Coll Dent, vol. 28, no. 4, pp. 128–133, Dec. 2016, doi: 10.12816/0033223.