title: An in vivo 3D micro-CT evaluation of tooth movement after the application of different force magnitudes in rat molar.
abstract: OBJECTIVE
  To investigate the precise longitudinal change in the periodontal ligament (PDL) space width and three-dimensional tooth movement with continuous-force magnitudes in living rats.
  
  
  METHODS
  Using nickel-titanium closed-coil springs for 28 days, 10-, 25-, 50-, and 100-g mesial force was applied to the maxillary left first molars. Micro-CT was taken in the same rat at 0, 1, 2, 3, 10, 14, and 28 days. The width of the PDL was measured in the pressure and tension sides from 0 to 3 days. Angular and linear measurements were used to evaluate molar position at day 0, 10, 14, and 28. The finite element model (FEM) was constructed to evaluate the initial stress distribution, molar displacement, and center of rotation of the molar.
  
  
  RESULTS
  The initial evaluation of PDL width showed no statistical differences among different force magnitudes. Tooth movement was registered 1 hour after force application and gradually increased with time. From day 10, greater tooth movement was observed when 10 g of force was applied. The FEM showed that the center of rotation in the molar is located in the center of five roots at the apical third of the molar roots.
  
  
  CONCLUSIONS
  The rat's molar movement mainly consists of mesial tipping, extrusion of distal roots, intrusion of mesial root, palatal inclination, and mesial rotation. Although the initial tooth movement after the application of different force magnitudes until day 3 was not remarkably different, 10 g of force produced more tooth movement compared with heavier forces at day 28.
authors.affiliation: Division of Orthodontics and Dentofacial Orthopedics, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
authors.forename: Carmen
authors.initials: C
authors.lastname: Gonzales
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hotokezaka
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Arai
authors.forename: Tadashi
authors.initials: T
authors.lastname: Ninomiya
authors.forename: Junya
authors.initials: J
authors.lastname: Tominaga
authors.forename: Insan
authors.initials: I
authors.lastname: Jang
authors.forename: Yuka
authors.initials: Y
authors.lastname: Hotokezaka
authors.forename: Motohiro
authors.initials: M
authors.lastname: Tanaka
authors.forename: Noriaki
authors.initials: N
authors.lastname: Yoshida
mesh_terms: D000818:Animals; D003799:Dental Stress Analysis / Q000379:methods; D020342:Finite Element Analysis; D021621:Imaging, Three-Dimensional; D008297:Male; D008963:Molar / Q000502:physiology; D010513:Periodontal Ligament / Q000000981:diagnostic imaging / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014087:Tooth Movement Techniques; D014092:Tooth Root / Q000502:physiology*; D055114:X-Ray Microtomography / Q000379:methods