1. Department of Orthodontics, West China College of Stomatology, Sichuan University, China
2. Department of Biomedical Engineering, Department of Orthodontics, University Medical Center Groningen, University of Groningen, The Netherlands
3. Department of Orthodontics, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
4. Department of Biomedical Engineering, FB40, University Medical Centre Groningen, PO Box 196, 9700 AD Groningen, The Netherlands