1. Division of Fixed Prosthodontics and Biomaterials University Clinic of Dental Medicine, University of Geneva Geneva 4 Switzerland
2. Clinic of Preventive Dentistry, Periodontology and Cariology, and Clinic of General, Special Care and Geriatric Dentistry, Center of Dental Medicine University of Zurich Zurich Switzerland
3. Division of Prosthodontics, Faculty of Dental Medicine University of Belgrade Belgrade Serbia