1. Oral Health Services, Health Centre of Pori, P.O. Box 33, 28601 Pori, Finland
2. Departments of Oral Development and Orthodontics and Public Health Dentistry, Institute of Dentistry, University of Turku, 20520 Turku, Finland
3. Department of Oral Development and Orthodontics, Institute of Dentistry, University of Oulu, 90014 Oulu, Finland