1. Department of Dental Hygiene, Hogeschool Arnhem Nijmegen University of Applied Sciences Nijmegen The Netherlands
2. Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA) University of Amsterdam, Vrije Universiteit Amsterdam Amsterdam The Netherlands
3. Division Clinical Methods and Public Health, Academic Medical Centre (AMC) University of Amsterdam Amsterdam The Netherlands
4. Department of Surgical, Medical Medical and Molecular Pathology and Critical Care Medicine University of Pisa Pisa Italy
5. Department of Periodontology UCL Eastman Dental Institute London UK