title: Microcomputed tomographic and biomechanical analysis of orthodontic microscrew stability under continuous or intermittent force.
abstract: OBJECTIVE
  To evaluate and compare the influence of continuous and intermittent forces on stability of titanium microscrews.
  
  
  METHODS
  One hundred forty-four microscrews were inserted bilaterally in the intraradicular zones of the maxillary first molar and second premolar in 36 beagles. Loads were delivered consecutively in the continuous group (n = 12), in cycles of 12 hours on/paused for 12 hours in intermittent group A (n = 12), and in cycles of 24 hours on/paused for 24 hours in intermittent group B (n = 12). The on/off cycles were repeated for 1, 3, 5, or 7 weeks, after which the animals were sacrificed, and microcomputed tomography (micro-CT) and pull-out testing were performed.
  
  
  RESULTS
  The micro-CT parameters of the microscrews in all three groups increased gradually with loading time. The value of peak load at extraction (Fmax) increased and reached a peak at week 5 but dropped slightly at week 7. In the continuous group, all measurements were lower than those in the intermittent groups at all times examined. All values in intermittent group A were higher than those in intermittent group B.
  
  
  CONCLUSIONS
  An intermittent loading regimen appears to be more favorable for obtaining stability than continuous loading, and a 12-hour/12-hour on/off loading cycle is superior to a 24-hour/24-hour on/off protocol in promoting bone-implant contact.
authors.forename: Yeke
authors.initials: Y
authors.lastname: Wu
authors.forename: Zheng
authors.initials: Z
authors.lastname: Jing
authors.forename: Wenlu
authors.initials: W
authors.lastname: Jiang
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Sun
authors.forename: Jingwen
authors.initials: J
authors.lastname: Zheng
authors.forename: Lijun
authors.initials: L
authors.lastname: Tan
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Zhao
authors.forename: Lixing
authors.initials: L
authors.lastname: Zhao
authors.forename: Pu
authors.initials: P
authors.lastname: Yang
authors.forename: Yu
authors.initials: Y
authors.lastname: Li
authors.forename: Tian
authors.initials: T
authors.lastname: Tang
mesh_terms: D000818:Animals; D001641:Bicuspid; D001863:Bone Screws; D059605:Dental Implant-Abutment Design; D003799:Dental Stress Analysis / Q000379:methods*; D004285:Dogs; D006801:Humans; D057893:Immediate Dental Implant Loading / Q000379:methods; D008297:Male; D008904:Miniaturization; D008963:Molar; D010507:Periodicity; D011897:Random Allocation; D013314:Stress, Mechanical; D013997:Time Factors; D014025:Titanium; D055114:X-Ray Microtomography
chemical_list: D014025:Titanium