1. University of Iceland; Faculty of Odontology; Reykjavik; Iceland
2. University of Berne School of Dental Medicine; Berne; Switzerland
3. Tufts University School of Dental Medicine; Boston; USA
4. Private practice; Hamburg; Germany
5. Institute of Social and Preventive Medicine; University of Berne; Switzerland
6. The University of Hong Kong; Faculty of Dentistry; Hong Kong; China