1. a Postgraduate student, Department of Orthodontics, Faculty of Dentistry, Hong Kong
2. b Professor, Department of Orthodontics, Faculty of Dentistry, Hong Kong
3. Corresponding author: Dr A. Bakr Rabie, Professor, Department of Orthodontics, Faculty of Dentistry, Prince Philip Dental Hospital, 34 Hospital Road, Hong Kong (rabie@hkusua.hku.hk)
4. c Associate Professor, Department of Orthodontics, Faculty of Dentistry, Hong Kong