1. Department of Operative Dentistry and Periodontology; University School of Dentistry; Freiburg; Germany
2. Department of Medical Biometry and Statistics; University School of Medicine; Freiburg; Germany
3. Department of Periodontology; University Hospital Carl Gustav Carus at the TU Dresden; Dresden; Germany
4. Department of Operative Dentistry and Periodontology; Johannes-Gutenberg University; Mainz; Germany
5. Department of Periodontology; Operative and Preventive Dentistry; University Dental Clinic; Bonn; Germany