1. Restorative Dental Sciences, Discipline of Endodontology, Faculty of Dentistry, The University of Hong Kong, Hong Kong Island, Hong Kong SAR, P. R. China
2. Department of Chemistry, State Key Laboratory of Environmental and Biological Analysis, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR, P. R. China
3. Applied Oral Sciences and Community Dental Care, Dental Materials Science, Faculty of Dentistry, The University of Hong Kong, Hong Kong Island, Hong Kong SAR, P. R. China
4. Division of Dentistry, The University of Manchester, Manchester M13 9PL, U.K.