1. Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research Department of Prosthodontics; College of Stomatology; Xi'an Jiaotong University; Xi'an 710004 P. R. China
2. State Key Laboratory of Military Stomatology; National Clinical Research Center for Oral Diseases; Shaanxi Key Laboratory of Stomatology; Department of Prosthodontics; School of Stomatology; The Fourth Military Medical University; Xi'an 710032 P. R. China
3. Department of Endodontics; The Dental College of Georgia; Augusta University; Augusta GA 30912 USA
4. Paediatric Dentistry Unit of the Faculty of Dentistry; Prince Philip Dental Hospital; University of Hong Kong; Hong Kong SAR 999077 P. R. China
5. Department of Prosthodontics; School and Hospital of Stomatology; Wuhan University; Wuhan 430079 P. R. China