1. Clinic for Conservative Dentistry and Periodontology; School for Dental Medicine; Christian-Albrechts-University Kiel; Kiel Germany
2. Clinic for Preventive and Paediatric Dentistry; University of Greifswald; Greifswald Germany
3. Department of Periodontology Academic Centre for Dentistry Amsterdam (ACTA); University of Amsterdam and VU University Amsterdam; Amsterdam The Netherlands