title: Incidence and severity of root resorption in orthodontically moved premolars in dogs.
abstract: OBJECTIVE
  To study treatment-related factors for external root resorption during orthodontic tooth movement.
  
  
  METHODS
  An experimental animal study.
  
  
  METHODS
  Department of Orthodontics and Oral Biology, University Medical Centre Nijmegen, The Netherlands. Twenty-four young adult beagle dogs.
  
  
  METHODS
  Mandibular premolars were bodily moved with continuous or intermittent controlled orthodontic forces of 10, 25, 50, 100, or 200 cN according to standardized protocols. At different points in time histomorphometry was performed to determine the severity of root resorption.
  
  
  METHODS
  Prevalence of root resorptions, defined as microscopically visible resorption lacunae in the dentin. Severity of resorption was defined by the length, relative length, depth, and surface area of each resorption area.
  
  
  RESULTS
  The incidence of root resorption increased with the duration of force application. After 14-17 weeks of force application root resorption was found at 94% of the root surfaces at pressure sides. The effect of force magnitude on the severity of root resorption was not statistically significant. The severity of root resorption was highly related to the force regimen. Continuous forces caused significantly more severe root resorption than intermittent forces. A strong correlation (0.60 < r < 0.68) was found between the amount of tooth movement and the severity of root resorption.
  
  
  CONCLUSIONS
  Root resorption increases with the duration of force application. The more teeth are displaced, the more root resorption will occur. Intermittent forces cause less severe root resorption than continuous forces, and force magnitude is probably not decisive for root resorption.
authors.affiliation: Department of Orthodontics and Oral Biology, University Medical Centre Nijmegen, The Netherlands. j.maltha@dent.umcn.nl
authors.forename: J C
authors.initials: JC
authors.lastname: Maltha
authors.forename: E J
authors.initials: EJ
authors.lastname: van Leeuwen
authors.forename: G E H M
authors.initials: GE
authors.lastname: Dijkman
authors.forename: A M
authors.initials: AM
authors.lastname: Kuijpers-Jagtman
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001641:Bicuspid; D003799:Dental Stress Analysis; D004285:Dogs; D008297:Male; D008334:Mandible; D009811:Odontometry; D012391:Root Resorption / Q000209:etiology* / Q000473:pathology*; D013997:Time Factors; D014087:Tooth Movement Techniques / Q000009:adverse effects*; D014092:Tooth Root / Q000473:pathology