title: Hounsfield unit change in root and alveolar bone during canine retraction.
abstract: BACKGROUND
  The objective of this study was to determine the Hounsfield unit (HU) changes in the alveolar bone and root surfaces during controlled canine retractions.
  
  
  METHODS
  Eighteen maxillary canine retraction patients were selected for this split-mouth design clinical trial. The canines in each patient were randomly assigned to receive either translation or controlled tipping treatment. Pretreatment and posttreatment cone-beam computed tomography scans of each patient were used to determine tooth movement direction and HU changes. The alveolar bone and root surface were divided into 108 divisions, respectively. The HUs in each division were measured. Mixed-model analysis of variance was applied to test the HU change distribution at the P <0.05 significance level.
  
  
  RESULTS
  The HU changes varied with the directions relative to the canine movement. The HU reductions occurred at the root surfaces. Larger reductions occurred in the divisions that were perpendicular to the moving direction. However, HUs decreased in the alveolar bone in the moving direction. The highest HU reduction was at the coronal level.
  
  
  CONCLUSIONS
  HU reduction occurs on the root surface in the direction perpendicular to tooth movement and in the alveolar bone in the direction of tooth movement when a canine is retracted.
authors.affiliation: Postgraduate student, Department of Mechanical Engineering, Indiana University-Purdue University, Indianapolis, Ind.
authors.forename: Feifei
authors.initials: F
authors.lastname: Jiang
authors.affiliation: Assistant professor, Department of Orthodontics and Oral Facial Genetics, Indiana University, Indianapolis, Ind.
authors.forename: Sean S-Y
authors.initials: SS
authors.lastname: Liu
authors.affiliation: Associate professor, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences and Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Zeyang
authors.initials: Z
authors.lastname: Xia
authors.affiliation: Visiting assistant professor, Department of Mechanical Engineering, Indiana University-Purdue University, Indianapolis, Ind.
authors.forename: Shuning
authors.initials: S
authors.lastname: Li
authors.affiliation: Professor and chair, Department of Mechanical Engineering, Indiana University-Purdue University, Indianapolis, Ind; professor, Department of Orthodontics and Oral Facial Genetics, Indiana University, Indianapolis, Ind. Electronic address: jchen3@iupui.edu.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.affiliation: Professor and chair, Department of Orthodontics and Oral Facial Genetics, Indiana University, Indianapolis, Ind.
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Kula
authors.affiliation: Biostatistician supervisor, Department of Biostatistics, Indiana University, Indianapolis, Ind.
authors.forename: George
authors.initials: G
authors.lastname: Eckert
mesh_terms: D000293:Adolescent; D000328:Adult; D000539:Alveolar Process / Q000000981:diagnostic imaging*; D015519:Bone Density / Q000502:physiology; D002648:Child; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003481:Cuspid / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008875:Middle Aged; D019516:Orthodontic Space Closure / Q000295:instrumentation / Q000379:methods; D009969:Orthodontic Wires; D011446:Prospective Studies; D014087:Tooth Movement Techniques / Q000295:instrumentation / Q000379:methods*; D014092:Tooth Root / Q000000981:diagnostic imaging*; D055815:Young Adult
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