1. Faculty of Dentistry, University of Hong Kong, Hong Kong SAR, China;
2. Division of Pediatric Dentistry, Hokkaido University, Graduate School of Dental Medicine, Sapporo, Hokkaido, Japan;
3. Department of Oral Biology and Maxillofacial Pathology, School of Dentistry, Medical College of Georgia, Augusta, GA 30912-1129, USA; and
4. Department of Cariology, Restorative Sciences and Endodontics, School of Dentistry, University of Michigan, Ann Arbor, MI, USA;