title: Histological evaluation of the effects of initially light and gradually increasing force on orthodontic tooth movement.
abstract: OBJECTIVE
  To investigate histologically the effect of initially light and gradually increasing force on tooth movement in the rat.
  
  
  METHODS
  Cuboids made of neodymium-iron-boron magnets (experimental groups) or titanium (control group) were bonded to the lingual surface of the right and left maxillary first molars of 18-week-old male Wistar rats. The initial distances between materials were 1.0 mm generating 4.96 gf (experimental group 1) and 1.5 mm generating 2.26 gf (experimental group 2). In three groups, rats were killed 1, 3, 7, 10, or 14 days after treatment. Histological sections were prepared and stained with hematoxylin and eosin or for tartrate-resistant acid phosphatase (TRAP) activity. The number of TRAP-positive osteoclasts was counted, and the relative hyalinized area was measured on the pressure side of periodontal ligament.
  
  
  RESULTS
  There were significant differences in the number of osteoclasts among the three groups (P < .05). On days 1 and 3, the numbers of osteoclasts in experimental group 2 were greater than in experimental group 1. There were significant differences in the relative hyalinized area between the control group and experimental group 1 (P < .01) and between experimental groups 1 and 2 (P < .01). On days 1 and 3, the hyalinized area in experimental group 1 was larger than in experimental group 2.
  
  
  CONCLUSIONS
  Initially light and gradually increasing force induced tooth movement without the lag phase and showed smooth recruitment of osteoclasts and inhibition of hyalinization.
authors.affiliation: Division of Orthodontics and Dentofacial Orthopedics, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Miyagi, Japan. ryotommy@mail.tains.tohoku.ac.jp
authors.forename: Ryo
authors.initials: R
authors.lastname: Tomizuka
authors.forename: Yoshinaka
authors.initials: Y
authors.lastname: Shimizu
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Kanetaka
authors.forename: Akihiro
authors.initials: A
authors.lastname: Suzuki
authors.forename: Sachiko
authors.initials: S
authors.lastname: Urayama
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Kikuchi
authors.forename: Hideo
authors.initials: H
authors.lastname: Mitani
authors.forename: Kaoru
authors.initials: K
authors.lastname: Igarashi
mesh_terms: D000135:Acid Phosphatase / Q000032:analysis; D000818:Animals; D002452:Cell Count; D007527:Isoenzymes / Q000032:analysis; D008297:Male; D008437:Maxilla / Q000201:enzymology; D010010:Osteoclasts / Q000166:cytology* / Q000201:enzymology; D010513:Periodontal Ligament / Q000166:cytology*; D011312:Pressure / Q000009:adverse effects; D051381:Rats; D017208:Rats, Wistar; D000071681:Tartrate-Resistant Acid Phosphatase; D013997:Time Factors; D014087:Tooth Movement Techniques
chemical_list: D007527:Isoenzymes; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase