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The effect of insertion angle on orthodontic mini-screw torque
Seyed Hamid Raji1, Saeed Noorollahian2, Seyed Mohsen Niknam1
1Torabinejad Research Center and Department of Orthodontics, Isfahan University of Medical Sciences, Isfahan, Iran.
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.
Materials And 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).
Conclusion:
Oblique insertion of the mini-screws results in higher insertion and removal torques and probably more primary stability compared to the vertical insertion.
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