1. Department of Periodontology; Philipps University Marburg; Marburg Germany
2. Clinic for Prosthetic Dentistry; University Iuliu Hatieganu; Cluj-Napoca Romania
3. Department for Statistics; Ludwig-Maximilians University; Munich Germany
4. Department of Periodontology; Faculty of dentistry; Malmö University; Malmö Sweden
5. Department of Periodontology; School of Dental Medicine; University of Bern; Bern Switzerland