1. Private Office Huerzeler/Zuhr; Munich Germany
2. Department of Operative Dentistry and Periodontology; University School of Dentistry; Albert-Ludwigs-University; Freiburg Germany
3. Department of Periodontology; Center for Dental, Oral and Maxillofacial Medicine (Carolinum); Johann Wolfgang Goethe University; Frankfurt/Main Germany
4. Clinic of Fixed and Removable Prosthodontics and Dental Material Science; Center of Dental Medicine; University of Zurich; Zurich Switzerland