[Morphology of bone threads following implantation of 2 mm AO miniscrews in the midfacial area].
How well an osteosynthesis screw holds depends on the amount of friction between the thread flank of the screw and the bone thread. Factors undermining the mechanical integrity of the bone thread, such as cracks, can lead to reduced friction and consequently less ability to hold. To investigate the micromorphology of the bone thread in the thin bone of the midface, 131 bony implant beds of 2-mm AO miniscrews and 10 drill holes which had been pretapped but received no screws were studied by incident light and scanning electron microscopy. The angle of insertion of the screws was varied to assess the effect this has on the implant bed surface. In 30 of the 131 implant beds the insertion axis of the screws corresponded to the axis of the threaded or unthreaded drill holes. Sixty-six of the screws had been inserted at an inclination of greater than or equal to 10 degrees to the axis of the pretapped hole. Twenty pretapped implant beds had an inclination between 0 degrees and 10 degrees to the drill hole. Finally, 15 bone threads formed by inclining the screws upon insertion into untapped drill holes were also studied. Both pretapped and untapped implant bed surfaces were damaged with cracks, as well as signs of squashing, crushing and shearing stress. The extent of the damage often varied in the different implant beds as well as at different locations in the same implant bed. The pretapped implant beds seemed to have a relatively smoother surface when the drill or threader and the screws had the same axis.(ABSTRACT TRUNCATED AT 250 WORDS)
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D001860:Bone Plates; D001863:Bone Screws; D005147:Facial Bones / Q000293:injuries*; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D012887:Skull Fractures / Q000601:surgery*
Morphologie des Knochengewindes nach Implantation von 2 mm-AO-Minischrauben im Mittelgesicht.