1. Department of Reconstructive Dentistry; Faculty of Odontology; University of Iceland; Reykjavik Iceland
2. Division of Fixed Prosthodontics and Biomaterials; University Clinics for Dental Medicine; University of Geneva; Geneva Switzerland
3. Institute of Social and Preventive Medicine; University of Bern; Bern Switzerland
4. Clinic of Fixed and Removable Prosthodontics and Material Science; University of Zurich; Zurich Switzerland