Sunday, 31 July 2011

JCO, Miniscrew Loosening, Prof B.Melsen

Prof. B. Melsen talks in simple words  about miniscrews and the reasons behind failure.
First of all the failure of miniscrews can be seen immediately (in the first couple of weeks) or later.

A summary of some of the points given in this article:

Early Failure:

  • Insufficient primary stability (wrong site selection, due to insufficient bone quality, or quantity)
  • Iatrogenic failures (jiggling during the insertion, over-screwing)
  • Magnitude and direction of the force loading (high magnitude of force, it is advised to start with around 50cN and increase the force gradually, also unscrewing moments should be avoided)
Later Failure:
  • Change of the local environment (inflammation due to root proximity, or change of the local bone turn over, e.g. in relation to resorption of the root of a deciduous tooth)
  • Systemic factors (such as smoking, alcoholism, and medication that influences bone turnover have been proven risk factors for implant failure in general)
In any case when a miniscrew fails, the new insertion site has to further away from the old one, at least twice the diameter of the screw. In addition choosing to change the site and use the screw with an indirect loading instead of direct could be advised if a screw fails more than once at the same patient.

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