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