title: Microcomputed tomographic analysis of bone reaction at insertion of orthodontic mini-implants in sheep.
abstract: OBJECTIVE
  To evaluate the effects on bone of forced insertion of self-tapping orthodontic mini-implants and thus obtain biomechanical data to develop insertion protocols and optimize drills for implant site preparation.
  
  
  METHODS
  After implant site preparation, 39 orthodontic mini-implants (OMI), 1.6 x 7.5 mm each, were inserted into the hard bone of sheep mandible; 24 were placed with a 1-mm bone drill and 15 were placed with a standard-diameter (1.2-mm) drill. Removal torque was measured immediately (group A) and 8 weeks after insertion (group B). Eight OMIs (group C) were removed from the mandible in block sections of appropriate size for microcomputed tomographic morphometric and morphologic analyses.
  
  
  RESULTS
  All OMIs were placed without complications, with mean insertion torque of 17.625 (± 1.71) Ncm (test groups) and 17.70 (± 1.41) (control groups) and were stable at reentry. Group A implants showed a reduction in removal torque of 5.66%, while in group B, removal torque was reduced by 43.25%. In the control groups (ie, OMIs placed with a 1.2-mm drill), removal torque immediately after placement was reduced by 5.64%, and 8 weeks after insertion, removal torque had declined by 18.2%. Microcomputed tomographic bone morphometric analysis for both test and control groups showed that bone-implant contact was lower than expected in cortical bone 8 weeks after insertion. Morphologic analysis revealed cavities in the cortical bone close to the surface and microcalli in soft bone. Cavities in the cortical bone may have been caused by bone trauma during insertion.
  
  
  CONCLUSIONS
  The use of a narrow drill for site preparation increased orthodontic screw insertion torque, but it also damaged the bone and decreased removal torque. Standard histologic examination may clarify whether cavities in hard bone are actually signs of bone resorption that results from the activation of remodeling.
authors.affiliation: University of Genoa, Italy. al.reb@tin.it
authors.forename: Alberto
authors.initials: A
authors.lastname: Rebaudi
authors.forename: Nicola
authors.initials: N
authors.lastname: Laffi
authors.forename: Stefano
authors.initials: S
authors.lastname: Benedicenti
authors.forename: Francesca
authors.initials: F
authors.lastname: Angiero
authors.forename: George E
authors.initials: GE
authors.lastname: Romanos
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003748:Dental Equipment; D015921:Dental Implants; D003799:Dental Stress Analysis; D004867:Equipment Design; D008334:Mandible / Q000502:physiology / Q000601:surgery*; D052280:Orthodontic Anchorage Procedures / Q000295:instrumentation / Q000379:methods*; D016348:Osseointegration / Q000502:physiology*; D010027:Osteotomy / Q000295:instrumentation; D012756:Sheep; D013314:Stress, Mechanical; D014945:Wound Healing / Q000502:physiology*; D055114:X-Ray Microtomography
chemical_list: D015921:Dental Implants