1. Department of Periodontology, Operative and Preventive Dentistry University Hospital Bonn Bonn Germany
2. Department of Preventive, Restorative and Pediatric Dentistry University of Bern Bern Switzerland
3. Preclinical Education and Dental Material Science Department of Prosthodontics University Hospital Bonn Bonn Germany
4. Department of Reconstructive Dentistry & Gerodontology University of Bern Bern Switzerland