1. Department of Stomatology, The Second Affiliated Hospital of Zhejiang Chinese Medical University, Hangzhou, Zhejiang 310085, P.R. China
2. Department of Stomatology, Zhejiang Hospital, Hangzhou, Zhejiang 310030, P.R. China
3. Department of General Dentistry, Boston University Henry M. Goldman School of Dental Medicine, Boston, MA 02118, USA