1. Department of Preventive and Pediatric Dentistry, University of Greifswald, 17489 Greifswald, Germany
2. Department of Pediatric Dentistry and Dental Public Health, Faculty of Dentistry, Cairo University, Cairo 12613, Egypt
3. School of Dentistry, Newgiza University, Giza 12577, Egypt
4. Department of Paediatric Dentistry, University Clinic of Dentistry, Medical University of Vienna, 1090 Vienna, Austria