Avraham Zini, Sgan-Cohen, Harold D, and Marcenes, Wagner . 2011. “Socio-Economic Position, Smoking, And Plaque: A Pathway To Severe Chronic Periodontitis”. Journal Of Clinical Periodontology, 38, Pp. 229 – 235. doi:10.1111/j.1600-051X.2010.01689.x.