1. State Key Laboratory of Military Stomatology, Department of Operative Dentistry and Endodontics, School of Stomatology, Fourth Military Medical University, 145 West Chang-le Road, Xi'an 710032, Shaanxi, P.R. China
2. Department of Stomatology, 81 Hospital of PLA, Nanjing 210000, Jiangsu, P.R. China