1. Early onset periodontitis in the United States of America;Löe;J Periodontol,1991
2. Occurrence of periodontitis in an urban adolescent population;Perry;J Periodontol,2003
3. World Health Organization What is the burden of oral disease? http://www.who.int/oral_health/disease_burden/global/en/
4. A global epidemic;Nowzari;Dimensions of Dent Hyg,2008