1. Department of Geriatric Dentistry; School and Hospital of Stomatology, Peking University; Beijing 100081 People's Republic of China
2. Department of Polymer Science and Engineering; MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Zhejiang University; Hangzhou 310027 People's Republic of China
3. Department of Oral and Maxillofacial Surgery; Affiliated Stomatology Hospital, College of Medicine, Zhejiang University; Hangzhou 310006 People's Republic of China
4. Zhoushan Stomatology Hospital; Zhoushan 316000 People's Republic of China