title: Primary stability and viscoelastic displacement of mini-implant system under loading.
abstract: BACKGROUND
  The objectives of the current study were to examine the effects of mini-implant diameters on 1) primary stability before bone properties are changed by active peri-implant bone remodeling and 2) the time-dependent displacement of mini-implant systems in bone under a functional radial loading and their associations with bone mineral density.
  
  
  METHODS
  Twenty one, 8mm length mini-implants (7 each for 1.4mm, 1.6mm, and 2mm diameters) were placed in mandibular sections of human cadavers (4 males and 3 females, average 69.7 (SD 13.1) years of age). Displacement of the mini-implant in wet bone was assessed during initial and subsequent continuous radial loading of 2N in the mediolateral direction for 2h. Mean, standard deviation and coefficient of variation of peri-implant bone mineral density were obtained using histograms of cone-beam computed tomography attenuation values. The cortical thickness along with the miniscrew site was also measured.
  
  
  RESULTS
  The primary stability and displacement of mini-implants in bone were not significantly different between the 3 diameter groups (p>0.147, n=21). Moderate positive correlations of time-dependent viscoelastic displacement (creep) were found with bone mineral density variability independent of the mini-implant diameters (p>0.11).
  
  
  CONCLUSIONS
  The post-implantation displacements of mini-implant suggested that the orthodontic treatment loading can develop micromotion between the mini-implant and surrounding bone leading to reduction of its primary stability. Current findings also provide an insight that peri-implant bone mineral density variability plays an important role in controlling displacement of the mini-implant, which determine its stability during early and prolonged orthodontic treatment loading periods.
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Lee
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: Yong-Hoon
authors.initials: YH
authors.lastname: Jeong
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Pittman
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: Toru
authors.initials: T
authors.lastname: Deguchi
authors.affiliation: Division of General Practice and Materials Science, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Johnston
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA.
authors.forename: Henry W
authors.initials: HW
authors.lastname: Fields
authors.affiliation: Division of Orthodontics, College of Dentistry, The Ohio State University, Columbus, OH, USA. Electronic address: kim.2508@osu.edu.
authors.forename: Do-Gyoon
authors.initials: DG
authors.lastname: Kim
mesh_terms: D000368:Aged; D015519:Bone Density; D016723:Bone Remodeling; D015921:Dental Implants; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000502:physiology / Q000601:surgery; D052280:Orthodontic Anchorage Procedures
chemical_list: D015921:Dental Implants
keywords: Bone mineral density; Creep; Diameter; Mini-implant; Orthodontic loading; Thickness