1. Department of Periodontology, Operative and Preventive Dentistry, University of Bonn, Welschnonnenstrasse 17, 53111 Bonn, Germany
2. Private Practice for Periodontology, Krefelder Strasse 73, 52070 Aachen, Germany
3. BIOCRAN Research Group, University Complutense of Madrid, 28040 Madrid, Spain
4. Department of Orthodontics, University of Bonn, Welschnonnenstrasse 17, 53111 Bonn, Germany
5. Private Practice for Orthodontics, Theaterstraße 98-102, 52062 Aachen, Germany
6. Private Practice, Corso Galileo Ferraris 148, 10129 Turino, Italy
7. ETEP Research Group, University Complutense of Madrid, 28040 Madrid, Spain
8. Institute for Medical Biometry, Informatics and Epidemiology, University of Bonn, 53127 Bonn, Germany