title: In-vitro impact of insertion angle on primary stability of miniscrews.
abstract: BACKGROUND
  The use of miniscrews as anchorage has become increasingly popular, but there is no consensus on the best insertion angle. The purpose of this study was to determine the impact of insertion angle on implant primary stability.
  
  
  METHODS
  Sixty-four miniscrews, 6 × 1.6 mm, were placed in 64 fresh bone segments from 32 sheep mandibles. The miniscrews were inserted into the bone surface at 4 angles: 30°, 45°, 60°, and 90°. The maximum resistance forces of miniscrews in pullout and shear tests were determined as primary stability using a universal testing machine.
  
  
  RESULTS
  In the pullout tests, the 90° insertion angle had the highest primary stability. Oblique angulations of the miniscrews resulted in lower resistance. In the shear tests, angulations of the miniscrews from 90° to 45° led to increased primary stability. A more oblique insertion (30°) resulted in reduced primary stability.
  
  
  CONCLUSIONS
  The direction of the applied force had a significant impact on the primary stability of miniscrews at various insertion angles. The highest primary stability values were achieved at 45° when the miniscrews were loaded by shear force and at 90° when pullout force was applied.
authors: Assistant professor, Orthodontic Department, School of Dentistry, Shahed University, Tehran, Iran.
authors: Mehdi
authors: M
authors: Araghbidikashani
authors: Assistant professor, Orthodontic Department, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran. Electronic address: a.golshah@kums.ac.ir.
authors: Amin
authors: A
authors: Golshah
authors: Assistant professor, Oral and Maxillofacial Radiology Department, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors: Nafiseh
authors: N
authors: Nikkerdar
authors: Assistant professor, Oral and Maxillofacial Surgery Department, School of Dentistry, Kermanshah University of Medical Sciences, Kermanshah, Iran.
authors: Majid
authors: M
authors: Rezaei
mesh_terms: D000818:Animals; D001732:Bite Force; D001863:Bone Screws; D004868:Equipment Failure; D066298:In Vitro Techniques; D008334:Mandible / Q000601:surgery*; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation* / Q000379:methods; D033081:Shear Strength; D012756:Sheep; D016474:Weight-Bearing