1. Department of Periodontology; Tufts University School of Dental Medicine; Boston; MA; USA
2. Private Practice; Torino; Italy
3. Institute of Social and Preventive Medicine; University of Bern; Switzerland
4. Department of Prosthetic Dentistry & Department of Oral and Maxillofacial Surgery; University Medical Center Groningen; University of Groningen; Groningen; The Netherlands