1. Department of Operative Dentistry and Periodontology, Faculty of Medicine University of Freiburg Freiburg Germany
2. Department of Medical Biometry and Statistics, Faculty of Medicine University of Freiburg Freiburg Germany
3. Policlinic of Operative Dentistry, Periodontology, and Pediatric Dentistry, Medical Faculty Carl Gustav Carus Technische Universität Dresden Dresden Germany
4. Hannover Medical School, Department of Conservative Dentistry Periodontology and Preventive Dentistry Hannover Germany