1. State Key Laboratory of Military Stomatology and National Clinical Research Center for Oral Diseases and Shaanxi Key Laboratory of Stomatology, Department of Operative Dentistry and Endodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, P.R. China.
2. Biomedical Sciences Department, Texas A&M University College of Dentistry, Dallas, Texas.
3. Department of Operative Dentistry and Endodontics, Weifang People's Hospital, Weifang, P.R. China.