1. Department of Community Dentistry; Faculty of Medicine; University of Oulu; Oulu Finland
2. Medical Research Center; Oulu University Hospital; Oulu Finland
3. Discipline of Dentistry; University of Kwazulu-Natal; Durban South Africa
4. National Institute of Health and Welfare (THL); Helsinki Finland
5. Institute of Clinical Dentistry; Arctic University of Norway; Tromsø Norway