1. Institute of Stomatology, Nanjing Medical University, Nanjing, Jiangsu, P.R. China.
2. Department of Endodontics, School of Stomatology, Fourth Military Medical University, Xi'an, Shaanxi, P.R. China.
3. Research and Development Center for Tissue Engineering, Fourth Military Medical University, Xi'an, Shaanxi, P.R. China.
4. Department of Oral Histology & Pathology, School of Stomatology, Fourth Military Medical University, Xi'an, Shaanxi, P.R. China.