1. Department of Oral Mucosal Diseases, State Key Laboratory of Military Stomatology & National Clinical Research Center for Oral Diseases & Shaanxi Key Laboratory of Stomatology, School of StomatologyThe Fourth Military Medical University 145 changle xi road, Xi'an Shaanxi 710032 China
2. Department of Endodontics, College of Graduate StudiesAugusta University 1430, John Wesley Gilbert Drive, Augusta GA 30912 U.S.A.