1. Department of Prosthodontics, Propaedeutics and Dental Materials; Christian-Albrechts University at Kiel; Kiel Germany
2. Department of Prosthodontics; University Hospital Freiburg; Freiburg Germany
3. Center for Clinical Studies; Christian-Albrechts University at Kiel; Kiel Germany
4. Center for Dental and Oral Medicine, Department of Dental Prosthetics; University Medical Center Hamburg Eppendorf; Hamburg Germany
5. Center of Dentistry, Department of Prosthetic Dentistry; Ulm University Hospital; Ulm Germany
6. Department of Prosthodontics; University Hospital Hannover; Hannover Germany
7. Department of Prosthodontics, Gerodontology and Biomaterials, Greifswald; University Hospital; Greifswald Germany
8. Department of Prosthetic Dentistry, Dresden University of Technology; University Carl Gustav Carus; Dresden Germany
9. Department of Prosthodontics; Heidelberg University Hospital; Heidelberg Germany
10. Department of Prosthodontics and Biomaterials; University Hospital Aachen; Aachen Germany