1. Department of Oral and Maxillofacial Surgery Faculty of Dentistry The University of Hong Kong Hong Kong SAR China
2. Oral Cancer Research Group Faculty of Dentistry The University of Hong Kong Hong Kong SAR China
3. Department of Oral Pathology, Radiology and Medicine College of Dentistry University of Iowa Iowa City IA USA
4. Department of Epidemiology College of Public Health University of Iowa Iowa City IA USA