title: Pullout strength of miniscrews placed in anterior mandibles of adult and adolescent dogs: a microcomputed tomographic analysis.
abstract: BACKGROUND
  Miniscrews often loosen during orthodontic treatment, especially in teenage patients. The purposes of this study were to explore the differences of the pullout strengths of miniscrews placed in the anterior mandibles of adolescent and adult dogs and the structural parameters of peri-miniscrew bone, and to analyze the correlation between the pullout strengths and the variables of the peri-miniscrew bone structure.
  
  
  METHODS
  Eight adult beagles and 8 young beagles with early permanent dentitions were used as experimental subjects. Two miniscrews were symmetrically placed in the anterior mandible of each dog several minutes before death. The bone density, relative bone volume, and cortical bone thickness were evaluated by micro-computed tomography, and the pullout strength of the miniscrew was tested with a testing machine. Regression analyses were used to study the relationship between pullout strength and bone density, relative bone volume, and cortical bone thickness.
  
  
  RESULTS
  The values of bone density, relative bone volume, cortical bone thickness, and pullout strength were 781.94 + or - 21.46 mg of hydroxyapatite per cubic centimeter, 0.62 + or - 0.33, 1.14 + or - 0.11 mm, and 218.40 + or - 24.50 N for the adult dogs; and 713.61 + or - 13.08 mg of hydroxyapatite per cubic centimeter, 0.57 + or - 0.20, 1.07 + or - 0.86 mm, and 130.82 + or - 2.20 N for the young dogs, respectively. All pairs of pullout force and bone structural parameters had significant correlation coefficients. The pullout force showed the strongest correlation with bone density and the weakest with cortical bone thickness.
  
  
  CONCLUSIONS
  The values of bone density, relative bone volume, cortical bone thickness, and the pullout strength of the adult group were higher than those of the young group. Furthermore, bone density is more sensitive in terms of showing pullout force compared with relative bone volume and cortical bone thickness.
authors.affiliation: Department of Orthodontics, Provincial Hospital affiliated with Shandong University, Jinan, China.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Wang
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Zhao
authors.forename: Jing
authors.initials: J
authors.lastname: Xue
authors.forename: Jinlin
authors.initials: J
authors.lastname: Song
authors.forename: Feng
authors.initials: F
authors.lastname: Deng
authors.forename: Pu
authors.initials: P
authors.lastname: Yang
mesh_terms: D000367:Age Factors; D000818:Animals; D015519:Bone Density / Q000502:physiology*; D001863:Bone Screws; D003758:Dental Implantation, Endosseous; D003799:Dental Stress Analysis; D004285:Dogs; D017886:Durapatite; D020007:Implants, Experimental; D008297:Male; D008334:Mandible / Q000033:anatomy & histology / Q000737:chemistry / Q000000981:diagnostic imaging / Q000601:surgery; D008904:Miniaturization; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D013718:Tensile Strength; D055114:X-Ray Microtomography
chemical_list: D017886:Durapatite