1. Department of Clinical Dentistry, Centre for Clinical Dental Research; University of Bergen; Norway
2. Department of Periodontology, Faculty of Odontology; Malmö University; Malmö Sweden
3. Department of Orthodontics and Dentofacial Orthopedics; University of Bern; Bern Switzerland
4. Stereology and Electron Microscopy Laboratory, Department of Clinical Medicine; Aarhus University; Aarhus Denmark