1. Unit of Orthodontics and Pediatric Dentistry, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, 27100 Pavia, Italy
2. Department of Surgical Sciences, C.I.R. Dental School, Section of Pediatric Dentistry, University of Turin, 10124 Turin, Italy
3. Unit of Dental Hygiene, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Pediatric Sciencies, University of Pavia, 27100 Pavia, Italy