title: Applications of cone-beam computed tomography to assess the effects of labial crown morphologies and collum angles on torque for maxillary anterior teeth.
abstract: BACKGROUND
  Currently, cone-beam computed tomography (CBCT) has been widely used because of its capacity to evaluate the anatomic structures of the maxilla, mandible, and teeth in 3 dimensions. However, articles about the use of CBCT to evaluate the relationships between the morphology of individual teeth and torque expression remain rare. In this study, we aimed to determine the influence of labial crown morphologies and collum angles on torque for maxillary anterior teeth using CBCT.
  
  
  METHODS
  A total of 206 extracted maxillary anterior teeth were selected to establish scanning models using dental wax, and they were scanned by CBCT. Three-dimensionally reconstructed images and median sagittal sections of the teeth were digitized and analyzed with AutoCAD software (Autodesk, San Rafael, Calif). The angle α, formed by the intersection of the tangent at a certain vertical height on the labial surface from the incisal edge with the crown long axis, and the collum angle, were measured.
  
  
  RESULTS
  The variations in angle α at different heights from the incisal edge for the same type of tooth were statistically significantly different (P <0.001). Moreover, the variations between collum angles and 0° for any type of maxillary anterior tooth were statistically significant (P <0.01).
  
  
  CONCLUSIONS
  This study suggested that there are great differences in labial crown morphologies and collum angles for maxillary anterior teeth between persons, indicating that the morphologies of these teeth do play important roles in torque variations.
authors.affiliation: Professor, Department of Stomatology, School of Medicine, Jinan University, Guangzhou, Guangdong, China; chief physician, Department of Orthodontics, First Affiliated Hospital of Jinan University, Guangzhou, Guangdong, China. Electronic address: kongwd@yahoo.com.
authors.forename: Wei-Dong
authors.initials: WD
authors.lastname: Kong
authors.affiliation: Postgraduate student, Department of Stomatology, School of Medicine, Jinan University, Guangzhou, Guangdong, China; resident, Department of Orthodontics, Foshan Chancheng Stomatological Hospital, Foshan, Guangdong, China.
authors.forename: Jun-Yu
authors.initials: JY
authors.lastname: Ke
authors.affiliation: Chief physician, Department of Orthodontics, Guangzhou Military Hospital, Guangzhou, Guangdong, China.
authors.forename: Xiang-Quan
authors.initials: XQ
authors.lastname: Hu
authors.affiliation: Assistant professor and associate chief physician, Department of Orthodontics, First Affiliated Hospital of Jinan University, Guangzhou, Guangdong, China.
authors.forename: Wu
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Postgraduate student, Department of Stomatology, School of Medicine, Jinan University, Guangzhou, Guangdong, China.
authors.forename: Shu-Shu
authors.initials: SS
authors.lastname: Li
authors.affiliation: Postgraduate student, Department of Stomatology, School of Medicine, Jinan University, Guangzhou, Guangdong, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Feng
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003481:Cuspid / Q000000981:diagnostic imaging / Q000502:physiology; D006801:Humans; D007180:Incisor / Q000000981:diagnostic imaging* / Q000502:physiology; D008437:Maxilla / Q000000981:diagnostic imaging; D019228:Tooth Crown / Q000000981:diagnostic imaging*; D019415:Torque