1Hess W. The Anatomy of the Root Canals of the Teeth of the Permanent Dentition [ M ]. Ist edi. London, UK: John Bale, Sons and Danielsson Ltd, 1925:4 -49.
2Thomas RP, Moule AJ, Bryant R. Root canal morphology of maxillary permanent first molar teeth at various ages[ J]. International Endodontie Journal, 1993, 26 ( 5 ) :257 - 267.
3Peiris HRD, Pitakotuwage TN, Takahashi M, et al. Root canal morphology of mandibular permanent molars at different ages [J]. International Endodontic Journal, 2008,41 ( 10 ) : 828 - 835.
2Fan B, Yang J, Gutmann JL, et al. Root canal systems in mandibular first premolars with C-shaped root configurations. Part I : Microcomputed tomography mapping of the radicular groove and associated root canal crosssections [ J ]. J Endod, 2008,34 (11): 1337 -1341.
3Fan B, Cheung GS, Fan M, et al. C-shaped canal system in mandibular second molars : part I- anatomical features [J]. J Endod, 2004, 30 (12): 899- 903.
4Gu Y, Lu Q, Wang H, et al. Root canal morphology of permanent three-rooted mandibular first molars-part I: pulp floor and root canal system [J]. J Endod, 2010, 36 (6) : 990 -994.
5Tu MG, Huang HL, Hsue SS, et al. Detection of permanent three-rooted mandibular first molars by cone-beam computed tomography imaging in Taiwan Residents individuals [ J ]. J Endod, 2009, 35 (4) : 503 -507.
9Song JS, Choi HJ, Jung IY, et al. The prevalence and morphologic classification of distolingual roots in the mandibular molars in a Korean population [J]. J Endod, 2010, 36 (4) : 653 - 657.
10van Valen L. A study of fluctuating asymmetry [ J ]. Evolution, 1962, 16 (2) :125 -142.
