1. University of Groningen, University Medical Center Groningen, Center for Dentistry and Oral Hygiene, Department of Restorative Dentistry, Groningen, The Netherlands
2. Buijs Tandartsen, Clinic for General Dentistry, Groningen, The Netherlands
3. University of Zurich, Center of Dental Medicine, Division of Dental Biomaterials, Clinic for Reconstructive Dentistry, Zurich, Switzerland
4. St. Antonius Hospital, Department of Oral Maxillofacial Surgery, Prosthodontics and Special Dental Care, Nieuwegein, The Netherlands
5. Martini Hospital, Department of Special Dental Care, Groningen, The Netherlands