1. Department of Periodontology; Academic Center for Dentistry Amsterdam (ACTA); University of Amsterdam and VU University Amsterdam; Amsterdam The Netherlands
2. Clinic for Dentistry; Bussum The Netherlands
3. Department of Dentistry and Oral Hygiene; University of Groningen; Groningen The Netherlands
4. Department of Medical Microbiology; University Medical Center Groningen; University of Groningen; Groningen The Netherlands
5. Clinic for Periodontology; Utrecht The Netherlands