1. Oral and Maxillofacial Second Ward, The First Hospital of Qiqihar, Qiqihar, Heilongjiang 161000, P.R. China
2. Department of Stomatology, The Third Affiliated Hospital of Qiqihar Medical University, Qiqihar, Heilongjiang 161000, P.R. China
3. Department of Stomatology, The Fourth People's Hospital of Shaanxi, Xi'an, Shaanxi 710043, P.R. China