Rennan Y Du1, Cynthia K Y Yiu1, Virginia C N Wong2, Colman P McGrath3. 1. Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China. 2. Department of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. 3. 3B12, Dental Public Health, Periodontology and Public Health, Faculty of Dentistry, The University of Hong Kong, 34 Hospital Road, Sai Ying Pun, Hong Kong SAR, China. mcgrathc@hkucc.hku.hk.