title: [Influence of the diameter and length of the mini-implant on the primary stability after loading with composite forces].
abstract: OBJECTIVE
  To investigate the influence of the diameter and length of the mini-implant on the primary stability after loading with composite forces (CF) which contained torque and horizontal forces (HF).
  
  
  METHODS
  Ninety-six finite element models were established by the combination of mini-implant and bone, diameters (1.2 mm, 1.6 mm, 2.0 mm) and length (6 mm, 8 mm, 10 mm, 12 mm). There were 12 sizes, each size corresponded with 8 models. Group HF (each size n = 4) was loaded with 1.96 N horizontal force and Group CF (each size n = 4) was loaded with composite force which contained 6 N·mm torque and 1.96 N horizontal force. The maximum displacement of mini-implant with different force directions, implant diameters and lengths were evaluated.
  
  
  RESULTS
  The effect of force direction on the displacement related to diameter of mini-implant. The maximum displacement under load with HF respectively was changed with the changing of diameter[1.2 mm: (7.71 ± 0.49) µm; 1.6 mm: (3.94 ± 0.31) µm; 2.0 mm: (2.32 ± 0.43) µm], which were smaller than the maximum displacement of Group CF [1.2 mm: (9.22 ± 0.63) µm; 1.6 mm: (4.62 ± 0.52) µm; 2.0 mm: (2.69 ± 0.49) µm] (P < 0.05). When diameter was 1.2 mm, the difference of the maximum displacement [(1.61 ± 0.22) µm] between Group HF and CF was more obvious than that when the diameter was 1.6 mm or 2.0 mm [(0.64 ± 0.12), (0.49 ± 0.06) µm] (P < 0.05).
  
  
  CONCLUSIONS
  The composite force had unfavorable effect on the primary stability of the mini-implant. The diameter of the mini-implant had better be larger than 1.2 mm when the composite forces were applied.
authors.affiliation: Department of Orthodontics, Sun Yat-sen University, Guangzhou, China.
authors.forename: Ying-juan
authors.initials: YJ
authors.lastname: Lu
authors.forename: Shao-hai
authors.initials: SH
authors.lastname: Chang
authors.forename: Hong
authors.initials: H
authors.lastname: Wu
authors.forename: Yan-song
authors.initials: YS
authors.lastname: Yu
authors.forename: Yu-shan
authors.initials: YS
authors.lastname: Ye
mesh_terms: D020342:Finite Element Analysis; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation*; D019415:Torque