G McKenna1, B Janssens2, M Srinivasan3, P Brocklehurst4, G Tsakos5. 1. Centre for Public Health, Queens University Belfast, Belfast, UK. 2. Department of Oral Health Sciences, Ghent University, Ghent, Belgium. 3. Centre of Dental Medicine, University of Zurich, Zurich, Switzerland. 4. NWORTH Clinical Trials Unit, Bangor University, Bangor, UK. 5. Department of Epidemiology and Public Health, University College London, London, UK.