title: Effects of gradually increasing force generated by permanent rare earth magnets for orthodontic tooth movement.
abstract: OBJECTIVE
  To examine the effects of gradually increasing force generated by permanent rare earth magnets for orthodontic tooth movement by using a novel experimental rat model and computer simulation.
  
  
  METHODS
  Fifty-five male rats (age 18 weeks) were used as animal experiments. Magnetic (experimental groups) or titanium (control group) cuboids (1.5 x 1.5 x 0.7 mm) were bonded to the lingual surface of the maxillary first molars. The initial distance between materials was 1.0 mm, generating 4.96 gf (experimental group I), or 1.5 mm, generating 2.26 gf (experimental group II). Tooth movement was measured and periodontal structures were observed with microfocus x-ray computed tomography radiographs.
  
  
  RESULTS
  The distance between the magnets decreased with time in experimental groups I and II (P < .001), whereas there was no tooth displacement in the control group. Experimental group I showed rapid tooth movement in the initial phase followed by slower tooth movement. Experimental group II showed gradual tooth movement. Horizontal sections on microfocus computed tomgraphy radiographs revealed no pathological changes, such as root resorption, on the compressed side in the experimental groups.
  
  
  CONCLUSIONS
  The initial light force and gradual increasing force in magnetic attractive force induced effective tooth movement in rats without inducing any pathological changes.
authors.affiliation: Division of Orthodontics and Dentofacial Orthopedics, Tohoku University Graduate School of Dentistry, Sendai, Japan. ryotommy@mail.tains.tohoku.ac.jp
authors.forename: Ryo
authors.initials: R
authors.lastname: Tomizuka
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Kanetaka
authors.forename: Yoshinaka
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Akihiro
authors.initials: A
authors.lastname: Suzuki
authors.forename: Kaoru
authors.initials: K
authors.lastname: Igarashi
authors.forename: Hideo
authors.initials: H
authors.lastname: Mitani
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003198:Computer Simulation; D003799:Dental Stress Analysis; D008280:Magnetics / Q000295:instrumentation*; D008297:Male; D008674:Metals, Rare Earth; D009967:Orthodontic Appliances; D051381:Rats; D017208:Rats, Wistar; D014087:Tooth Movement Techniques / Q000295:instrumentation*
chemical_list: D008674:Metals, Rare Earth