title: Effects of placement angle and direction of orthopedic force application on the stability of orthodontic miniscrews.
abstract: OBJECTIVE
  To evaluate the influence of placement angle and direction of orthopedic force application on the stability of miniscrews.
  
  
  METHODS
  Finite element analysis was performed using miniscrews inserted into supporting bone at angles of 90°, 60°, and 30° (P90°, P60°, and P30°). An orthopedic heavy force of 800 gf was applied to the heads of the miniscrews in four upward (U0°, U30°, U60°, U90°) or lateral (L0°, L30°, L60°, L90°) directions. In addition, pull-out strength of the miniscrews was measured with various force directions and cortical bone thicknesses.
  
  
  RESULTS
  Miniscrews with a placement angle of 30° (P30°) and 60° (P60°) showed a significant increase in maximum von Mises stress following the increase in lateral force vectors (U30°, U60°, U90°) compared to those with a placement angle of 90° (P90°). In accordance, the pull-out strength was higher with the axial upward force when compared to the upward force with lateral vectors. Maximum von Mises stress and displacement of the miniscrew increased as the angle of lateral force increased (L30°, L60°, L90°). However, a more dramatic increase in maximum von Mises stress was noted in P30° than in P60° and P90°.
  
  
  CONCLUSIONS
  Placement of the miniscrew perpendicular to the cortical bone is advantageous in terms of biomechanical stability. Placement angles of less than 60° can reduce the stability of miniscrews when orthopedic forces are applied in various directions.
authors.affiliation: Department of Orthodontics, College of Dentistry, Yonsei University, Seoul, Korea.
authors.forename: Jihye
authors.initials: J
authors.lastname: Lee
authors.forename: Ji Young
authors.initials: JY
authors.lastname: Kim
authors.forename: Yoon Jeong
authors.initials: YJ
authors.lastname: Choi
authors.forename: Kyung-Ho
authors.initials: KH
authors.lastname: Kim
authors.forename: Chooryung J
authors.initials: CJ
authors.lastname: Chung
mesh_terms: D001696:Biomechanical Phenomena; D001863:Bone Screws; D019245:Compressive Strength; D003198:Computer Simulation; D055119:Elastic Modulus; D004548:Elasticity; D004853:Epoxy Resins / Q000737:chemistry; D020342:Finite Element Analysis; D005898:Glass / Q000737:chemistry; D006801:Humans; D007568:Jaw / Q000502:physiology; D055595:Mechanical Phenomena; D008904:Miniaturization; D008953:Models, Anatomic; D008954:Models, Biological; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000379:methods; D011140:Polyurethanes / Q000737:chemistry; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D004853:Epoxy Resins; D011140:Polyurethanes