Periodontal Research Group, The University of Birmingham, Birmingham, UK. Department of Periodontology, Service of Odontology, Rothschild Hospital, AP-HP, Paris 7-Denis Diderot University, U.F.R. of Odontology, Paris, France. EA 2496, Paris 5-Descartes University, U.F.R. of Odontology, Paris, France. WHO Collaboration Centre for Epidemiology and Community Dentistry, Milan, Italy. Department of Surgery, Microsurgery and Medicine Sciences, School of Dentistry, Universita degli Studi di Sassari, Sassari, Italy. INSERM, U1018, Villejuif, France. Centre for Oral Clinical Research, Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University London (QMUL), London, UK. Public Health Sciences, University of Washington, Seattle, WA, USA. Department of Periodontology, Academic Centre for Dentistry in Amsterdam, Amsterdam, the Netherlands. Department of Cariology, Institute of Odontology, Gothenburg, Sweden. Melbourne Dental School, University of Melbourne, Parkville, Vic., Australia. Faculty of Dentistry, Universidad Complutense de Madrid, Madrid, Spain. Dental Innovation and Translation Centre, Dental Institute, Kings College London, London, UK. Division for Cariology, Department of Operative Dentistry and Periodontology, Center for Dental Medicine, University Medical Center, Albert-Ludwig-University, Freiburg, Germany. Periodontology, K. U. Leuven, Leuven, Belgium. Faculty of Health and Medical Sciences, School of Dentistry, Section of Cariology and Endodontics, University of Copenhagen, Copenhagen, Denmark. Department of Cariology, Academic Centre for Dentistry Amsterdam, Amsterdam, the Netherlands. Oral Biology, University of Pittsburgh, Pittsburgh, PA, USA. Department of Special Care Dentistry, Dental School, Witten/Herdecke University, Witten, Germany.