title: Evaluation of the effect of force direction on stationary anchorage success of mini-implant with a lever-arm-shaped upper structure.
abstract: OBJECTIVE
  To compare the effect of clockwise and counterclockwise torque on the primary stability of a mini-implant with a lever-arm-shaped upper structure.
  
  
  METHODS
  Twenty-four white rabbits were used for this study. Two screw-type mini-implants were placed in each tibia. In all, 96 screws were inserted. Two weeks later, a 2-N force was applied to the mini-implants without an upper structure in eight rabbits (control group). The mini-implants of the other 16 rabbits were loaded with an upper structure (experimental group). In the experimental group, the two left mini-implants were loaded in a clockwise direction (CW group) and the two right implants were loaded in a counterclockwise direction (CCW group). The rabbits were sacrificed at 1 week or 8 weeks after loading in both control and experimental groups. The removal torque value (RTV) was measured in 15 of 16 mini-implants in each group and the remaining implant was processed for histologic examination.
  
  
  RESULTS
  At 1 week there were no significant differences in the mean RTV between the control, CW, and CCW groups. At 8 weeks, the RTV was higher in the control and experimental groups than in the respective 1-week groups. At 8 weeks, there were no significant differences in the RTV between the control and CW groups, but the CCW group showed a lower RTV.
  
  
  CONCLUSIONS
  CCW torque can decrease the stability of a mini-implant, whereas a CW torque has no effect.
authors: Department of Orthodontics, Kyung Hee University, Seoul, South Korea.
authors: Ki-Ho
authors: KH
authors: Park
authors: Eun-Man
authors: EM
authors: Lee
authors: Seung-Il
authors: SI
authors: Shin
authors: Seong-Hun
authors: SH
authors: Kim
authors: Young-Guk
authors: YG
authors: Park
authors: Su-Jung
authors: SJ
authors: Kim
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