Ivanka Mihaylova,
Faculty of Dental Medicine, Department of Dental Public Health, Medical University, Sofia, Bulgaria.
Email: ivanka.vasileva@fdm.mu-sofia.bg
Wolf-Dieter Grimm,
Department of Dental Medicine, Faculty of Health, Witten/Herdecke University, 58455 Witten, Germany.
Email: prof_wolf.grimm@yahoo.de
