1. State Key Laboratory of Military Stomatology; School of Stomatology; Fourth Military Medical University; 710032 Xi'an P. R. China
2. National Clinical Research Center for Oral Diseases; Department of Periodontology; School of Stomatology; Fourth Military Medical University; 710032 Xi'an P. R. China
3. Shaanxi Engineering Research Center for Dental Materials, and Advanced Manufacture; Biomaterials Unit; School of Stomatology; Fourth Military Medical University; 710032 Xi'an P. R. China