1. Department of Prosthetic Dentistry, Medical Center—University of Freiburg, Faculty of Medicine, University of Freiburg, 79106 Freiburg, Germany
2. Institute for Medical Biometry and Statistics, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany
3. Private Dental Clinic, Am Dorfplatz 3, 78658 Zimmern ob Rottweil, Germany