title: The effect of insertion angle on orthodontic mini-screw torque.
abstract: BACKGROUND
  Primary stability is an important factor for the clinical success of orthodontic mini-screws. The present study made an attempt to evaluate the effect of insertion angle changes on the maximum insertion and removal torque of orthodontic mini-screws.
  
  
  METHODS
  In this experimental study, 72 mini-screws (Dual Top Anchor System, Jeil, 1.6 mm diameter, 8 mm length) were used. They were randomly divided into four equal groups and inserted in poly-carbonate plates with 3 mm thickness. Then, their maximum insertion torque (MIT) and maximum removal torque (MRT) were recorded using a digital torque tester/screwdriver. Each group had a different insertion angle (90°, 75°, 60° and 45°). The data were analyzed by SPSS software (version 18) using one-way ANOVA and post-hoc Tukey's tests. The level of significance was set at 0.05.
  
  
  RESULTS
  The maximum MIT was observed in 45° insertion angle (14.84 Ncm) and the minimum MIT was reported in 75° insertion angle (12.66 Ncm). The maximum MRT was observed in 45° insertion angle (23.21 Ncm) and the minimum MRT was reported in the 90° insertion angle (17.43 Ncm).
  
  
  CONCLUSIONS
  Oblique insertion of the mini-screws results in higher insertion and removal torques and probably more primary stability compared to the vertical insertion.
authors.affiliation: Torabinejad Research Center and Department of Orthodontics, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Seyed Hamid
authors.initials: SH
authors.lastname: Raji
authors.affiliation: Dental Implants Research Center and Department of Orthodontics, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Saeed
authors.initials: S
authors.lastname: Noorollahian
authors.affiliation: Torabinejad Research Center and Department of Orthodontics, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Seyed Mohsen
authors.initials: SM
authors.lastname: Niknam
keywords: Insertion torque; orthodontic mini-screw; removal torque; skeletal anchorage