1. Department of Prosthodontics; University Medical Center Goettingen; Germany
2. Private Practice; Hanau Germany
3. Department of Medical Statistics. University Medical Center Goettingen; Germany
4. Department of Prosthodontics. University Medical Center Goettingen; Germany
5. Department of Restorative Dentistry and Periodontology; University Medical Center Leipzig; Germany
6. Department of Restorative Dentistry and Periodontology. University Medical Center Leipzig; Germany