1. University Medical Center Groningen; Center for Dentistry and Oral Hygiene; Department of Fixed and Removable Prosthodontics and Biomaterials; The University of Groningen; Groningen The Netherlands
2. Medical Center Groningen; Department of Epidemiology; The University of Groningen; Groningen The Netherlands
3. University Medical Center Groningen, Groningen; Department of Oral and Maxillofacial Surgery; The University of Groningen; Groningen The Netherlands
4. Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care; St. Antonius Hospital; Nieuwegein The Netherlands