1. State Key Laboratory of Organic−Inorganic Composites, Beijing Laboratory of Biomedical Materials, Beijing University of Chemical Technology, Beijing 100029, P. R. China
2. Department of Stomatology, Tianjin Medical University General Hospital, Tianjin 300052, P. R. China
3. Department of Endodontics, School and Hospital of Stomatology, Tianjin Medical University, Tianjin 300070, P. R. China