1. The University of Hong Kong; Dental Public Health, Faculty of Dentistry; 3B20, 3/F, Prince Philip Dental Hospital 34 Hospital Road Hong Kong China
2. School of Dentistry, The University of Manchester; Cochrane Oral Health Group; Coupland III Building, Oxford Road Manchester UK M13 9PL
3. Queen Mary University of London; Clinical and Diagnostic Oral Sciences, Barts and The London School of Medicine and Dentistry; Turner Street Whitechapel London UK E1 2AD