1. Department of Oral Histology and Pathology, School of Stomatology, The Fourth Military Medical University, Xi'an, P.R. China.
2. Research and Development Center for Tissue Engineering, The Fourth Military Medical University, Xi'an, P.R. China.
3. Department of Oral and Maxillofacial Surgery, School of Stomatology, The Fourth Military Medical University, Xi'an, P.R. China.