1. a Research Associate, Department of Orthodontics, Johannes Gutenberg University, Mainz, Germany
2. b Staff Dentist, Medical Corps, Husum Airbase, Germany
3. c Professor, Department of Orthodontics, Johannes Gutenberg-University, Mainz, Germany
4. d Professor, Academic Centre for Dentistry Amsterdam (ACTA), The Netherlands
5. Corresponding author: Professor Andrej Zentner, Department of Orthodontics, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA Amsterdam, The Netherlands (azentner@acta.nl)