title: Stability consideration for internal maxillary distractors.
abstract: OBJECTIVE
  Stability in distractor design ensures distraction osteogenesis healing with good bone regenerate formation. The aim of this study was to compare the holding strengths of different fixation systems for maxillary distractor design on bone pieces of different thicknesses.
  
  
  METHODS
  Cross-sectional images of 10 dry skulls were obtained by computer tomography and the bone thickness of the maxillae were measured according to five individual anatomical regions (paranasal, infra-orbital, posterior sinus wall, zygomatic and alveolar regions). According to the measurements, the screws of 1.5 and 2mm in diameter and the three-screw mini-plates in triangular and straight configurations were evaluated for holding strength by pull-out tests on fresh animal bone pieces of defined thickness.
  
  
  RESULTS
  The paranasal and zygomatic regions of the human skulls had the thickest cortical bone (4mm) followed by the alveolar region (2mm). In the bones of 2 and 4mm thickness, the 2mm screws were confirmed stronger than the 1.5mm ones in pull-out tests. However, the pull-out behaviour of screws of different diameters in 1mm thick bones and the mini-plates in two different configurations showed no significant differences.
  
  
  CONCLUSIONS
  This study confirms that the paranasal and zygomatic bones are the thickest for fixation of internal maxillary distractors. Fixation screws of 2mm diameter in either triangular or straight miniplates can produce good stabilization for distractors.
authors.affiliation: Discipline of Oral and Maxillofacial Surgery, Faculty of Dentistry, The University of Hong Kong, Hong Kong. lkcheung@hkucc.hku.hk
authors.forename: Lim K
authors.initials: LK
authors.lastname: Cheung
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhang
authors.forename: Martin C M
authors.initials: MC
authors.lastname: Wong
authors.forename: Lisa L S
authors.initials: LL
authors.lastname: Wong
mesh_terms: D000704:Analysis of Variance; D015519:Bone Density; D001860:Bone Plates; D001863:Bone Screws; D003799:Dental Stress Analysis; D004867:Equipment Design; D006801:Humans; D016268:Internal Fixators; D008437:Maxilla / Q000503:physiopathology / Q000601:surgery*; D019647:Oral Surgical Procedures / Q000295:instrumentation*; D019857:Osteogenesis, Distraction / Q000295:instrumentation*; D010256:Paranasal Sinuses / Q000033:anatomy & histology; D015050:Zygoma / Q000033:anatomy & histology