title: Orthodontic mini-implant stability under continuous or intermittent loading: a histomorphometric and biomechanical analysis.
abstract: BACKGROUND
  Both continuous and intermittent loadings are commonly applied in orthodontics. Clinical experiences and some studies believed that longer duration of force produce more effect (tooth movement, suture expansion, bone remodeling) than transient forces applied with the same magnitude. Alternatively, others indicated that interruption or recovery periods of various periods between loadings cause more bone remodeling and less root resorption. Therefore, which force is more favorable for osseointegration and stability of orthodontic mini-implant remains to be elucidated.
  
  
  OBJECTIVE
  To evaluate the influence of continuous or intermittent loading on stability of titanium mini-implants.
  
  
  METHODS
  One hundred ninety-two mini-implants were implanted bilaterally in intraradicular zones of mandibular M1 and P2 in 48 beagles. Loadings were delivered consecutively in continuous group, pauses were given for the last 3 or 7 days of each 2-week reactivation period for intermittent group A and B, respectively. The group unloaded was set as control. After 2, 4, 6 and 8 weeks, the animals were sacrificed and microscopic computerized tomography (μCT), histomorphological observation and pull-out test were applied.
  
  
  RESULTS
  The μCT parameters of mini-implants in four groups were gradually increased with loading time prolonged, while the value of peak load at extraction (F(max)) increased and reached summit at week 6, but dropped slightly at week 8. In continuous group, all measurements were lower than those in intermittent groups at all time points (p < .05), and all values in intermittent group B were higher than those in intermittent group A. Histomorphology observation revealed different degrees of bone remodeling with new bone formation in the peri-implants region in different groups.
  
  
  CONCLUSIONS
  Intermittent loading regimen is more favorable for obtaining stability than continuous force.
authors.affiliation: State Key Laboratory of Oral Diseases, Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China.
authors.forename: Yeke
authors.initials: Y
authors.lastname: Wu
authors.forename: Zhenrui
authors.initials: Z
authors.lastname: Xu
authors.forename: Luyuan
authors.initials: L
authors.lastname: Tan
authors.forename: Lijun
authors.initials: L
authors.lastname: Tan
authors.forename: Zhihe
authors.initials: Z
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
authors.forename: Lixing
authors.initials: L
authors.lastname: Zhao
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003758:Dental Implantation, Endosseous / Q000379:methods*; D015921:Dental Implants; D004285:Dogs; D021621:Imaging, Three-Dimensional; D008334:Mandible / Q000000981:diagnostic imaging / Q000601:surgery*; D052280:Orthodontic Anchorage Procedures; D016348:Osseointegration; D011897:Random Allocation; D013314:Stress, Mechanical; D014025:Titanium; D055114:X-Ray Microtomography
chemical_list: D015921:Dental Implants; D014025:Titanium
keywords: continuous force; intermittent force; mini-implants; osseointegration; stability