1. Department of Stomatology, The Affiliated Hospital of Hebei University, Baoding, Hebei 071000, P.R. China
2. Department of Stomatology, Laiyuan County Hospital of Traditional Chinese Medicine, Baoding, Hebei 074300, P.R. China
3. Department of Stomatology, Anguo City Hospital, Baoding, Hebei 071200, P.R. China
4. Galactophore Department, The Affiliated Hospital of Hebei University, Baoding, Hebei 071000, P.R. China
5. Department of Stomatology, The Second Hospital of Baoding City, Baoding, Hebei 071000, P.R. China