title: Effects of screw and host factors on insertion torque and pullout strength.
abstract: OBJECTIVE
  To experimentally study the effects of altering implant length, outer diameter, cortical bone thickness, and cortical bone density on the primary stability of orthodontic miniscrew implants (MSIs).
  
  
  METHODS
  Maximum insertion torque (IT) and pullout strength (POS) of 216 MSIs were measured in synthetic bone with different cortical densities (0.64 g/cc or 0.55 g/cc) and cortical thicknesses (1 mm or 2 mm). Three MSIs were evaluated: 6-mm long/1.75-mm outer diameter, 3-mm long/1.75-mm outer diameter, and 3-mm long/2.0-mm outer diameter. To test POS, a vertical force was applied at the rate of 5 mm/min until failure occurred.
  
  
  RESULTS
  The 6-mm MSIs displayed significantly (P < .001) higher IT and POS than the 3-mm MSIs did. The 3-mm MSIs with 2.0-mm outer diameters showed significantly higher (P < .001) IT and POS than the 3-mm MSIs with 1.75-mm outer diameters. The IT and POS were significantly (P < .001) greater for the MSIs placed in thicker and denser cortical bone.
  
  
  CONCLUSIONS
  Both outer diameter and length affect the stability of MSIs. Increases in cortical bone thickness and cortical bone density increase the primary stability of the MSIs.
authors.affiliation: Department of Orthodontics, Orthodontic Department, St Louis University, St Louis, MO, USA.
authors.forename: Ankit H
authors.initials: AH
authors.lastname: Shah
authors.forename: Rolf G
authors.initials: RG
authors.lastname: Behrents
authors.forename: Ki Beom
authors.initials: KB
authors.lastname: Kim
authors.forename: Hee-Moon
authors.initials: HM
authors.lastname: Kyung
authors.forename: Peter H
authors.initials: PH
authors.lastname: Buschang
mesh_terms: D000704:Analysis of Variance; D015519:Bone Density; D001863:Bone Screws; D018786:Bone Substitutes / Q000737:chemistry*; D015921:Dental Implants; D008422:Materials Testing; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D013314:Stress, Mechanical; D019415:Torque
chemical_list: D018786:Bone Substitutes; D015921:Dental Implants