1. Dept. of Periodontology, Charité University Medical Center, Campus Virchow, Augustenburger Platz 1, 13353 Berlin, Germany;
2. Institute for Social Medicine, Epidemiology and Health Economics, Charité University Medical Center, Berlin, Germany; and
3. Dept. of Epidemiology, German Institute of Human Nutrition, Potsdam-Rehbruecke, Germany