title: An evaluation of insertion sites for mini-implants: a micro - CT study of human autopsy material.
abstract: OBJECTIVE
  (1) To report the thickness of the cortical bone in insertion sites commonly used for orthodontic mini-implants, (2) to assess the impact of a change in insertion angle on primary cortical bone-to-implant contact, and (3) to evaluate the risk of maxillary sinus perforation.
  
  
  METHODS
  At autopsy, 27 human samples containing three to five adjacent teeth were excised and scanned using a table-top micro-computed tomography system. Bone thickness measurements were taken at 45° and 90° to the long the axis of the adjacent teeth, simulating a mini-implant insertion at the mid-root level.
  
  
  RESULTS
  In the maxilla, the overall mean cortical thickness at 90° was 0.7 mm buccally in the lateral region, 1.0 mm buccally in the anterior region, and 1.3 mm palatally. In the mandible, the mean cortical thickness was 0.7 mm buccally and 1.8 mm lingually in the anterior region; 1.9 mm buccally and 2.6 mm lingually in the lateral region. Changing the insertion angle from 90° to 45° increased the cortical bone-to-implant contact by an average of 47%. Perpendicular insertion at the mid-root level only rarely interfered with the sinus, whereas apically inclined insertion increased the risk of sinus perforation.
  
  
  CONCLUSIONS
  Buccally and palatally in the maxilla and buccally in the anterior mandible, the thickness of the alveolar cortical bone is often less than 1 mm. In contrast, the alveolar cortical bone is frequently thicker than 2 mm laterally in the mandible. Changing the insertion angle to 45° will generally enhance implant stability but increase the risk of perforation to the maxillary sinus.
authors.affiliation: Clinical Assistant Professor, Department of Orthodontics, School of Dentistry, Health, Aarhus University, Denmark. Private practice, Aarhus, Denmark. mortengl@yahoo.com
authors.forename: Morten G
authors.initials: MG
authors.lastname: Laursen
authors.forename: Birte
authors.initials: B
authors.lastname: Melsen
authors.forename: Paolo M
authors.initials: PM
authors.lastname: Cattaneo
mesh_terms: D000328:Adult; D000539:Alveolar Process / Q000033:anatomy & histology* / Q000000981:diagnostic imaging* / Q000601:surgery; D015519:Bone Density; D002102:Cadaver; D003758:Dental Implantation, Endosseous / Q000009:adverse effects / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008443:Maxillary Sinus / Q000293:injuries*; D008875:Middle Aged; D009297:Nasal Mucosa / Q000293:injuries; D052280:Orthodontic Anchorage Procedures / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D016348:Osseointegration; D012306:Risk; D055114:X-Ray Microtomography; D055815:Young Adult