title: An in vitro study of factors affecting the primary stability of orthodontic mini-implants.
abstract: OBJECTIVE
  To evaluate the effects of mini-implant features (length, design, core diameter), insertion technique (insertion angle, cortical punch), and cortical bone depth and density on mini-implant primary stability. The effect of mini-implant reinsertion was also investigated.
  
  
  METHODS
  Two hundred and sixty Infinitas mini-implants of two lengths (9 mm and 6 mm), two core diameters (0.8 mm and 0.9 mm) for an external diameter of 1.5 mm, and four designs (two tapered, external diameter 1.5 mm; two cylindrical, external diameters 1.5 mm and 2.0 mm) were inserted into synthetic bone blocks, and the maximum insertion torque (MIT) was recorded. The cortical layer of the blocks varied in density (30 and 50 lb per cubic foot) and depth (1 mm and 2 mm). Three angles of insertion (90°, 75°, and 60°) and two methods of insertion (direct and cortical punch) were tested. Forty mini-implants were also removed and reinserted.
  
  
  RESULTS
  A significant increase in the average MIT occurred when cortical bone density increased and when mini-implants were reinserted. The 1.5 mm diameter cylindrical design had significantly lower MIT than the 1.5 mm tapered and the 2.0 mm cylindrical designs. The other variables did not have a significant effect on MIT.
  
  
  CONCLUSIONS
  Mini-implants achieved greater primary stability in higher-density cortical bone, and the 1.5 mm diameter tapered and 2.0 mm cylindrical designs offered greater primary stability than the 1.5 mm cylindrical design. Reinserting mini-implants resulted in significantly increased MIT, possibly because of blunting of the threads.
authors.affiliation: Department of Orthodontics, Peterborough City Hospital, United Kingdom.
authors.forename: Lindsy
authors.initials: L
authors.lastname: Holm
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Cunningham
authors.forename: Aviva
authors.initials: A
authors.lastname: Petrie
authors.forename: Richard R J
authors.initials: RR
authors.lastname: Cousley
mesh_terms: D015519:Bone Density; D018786:Bone Substitutes / Q000737:chemistry*; D015921:Dental Implants; D003799:Dental Stress Analysis; D052280:Orthodontic Anchorage Procedures / Q000379:methods*; D016382:Orthodontic Appliance Design; D012044:Regression Analysis; D018709:Statistics, Nonparametric; D019415:Torque
chemical_list: D018786:Bone Substitutes; D015921:Dental Implants