1. Depertment of Surgical, Microsurgical and Medical Sciences, University of Sassari, Sassari, Italy
2. World Health Organization, Collaborating Centre for Epidemiology and Preventive Dentistry, Milan, Italy
3. Department of Biomedical, Surgical and Dental Sciences, University of Milan, Milan, Lombardia, Italy
4. Department of Oral and Maxillo Facial Sciences, University of Rome La Sapienza, Rome, Lazio, Italy