1. Periodontology Unit, Eastman Dental Hospital, University College London (UCL), London, UK;
2. Eastman Dental Hospital, UCLH NHS Foundation Trust, London, UK;
3. Division of Microbial Diseases, Eastman Dental Institute, UCL, London, UK;
4. Division of Periodontology, Department of Oral Health and Diagnostic Sciences, School of Dental Medicine, University of Connecticut Health Science Center, Farmington, USA; and
5. Department of Adult Dental Care, School of Clinical Dentistry, Claremont Crescent, Sheffield S10 2TA, UK