Orthodontic Corner: The stability of miniscrew placement, Editor's Corner, JCO Jan 2011

Thursday 20 January 2011

The stability of miniscrew placement, Editor's Corner, JCO Jan 2011

The Journal of Clinical Orthodontics published the results of an ongoing survey concerning the failure rate and the factors that are influencing the stability of miniscrew placement.

A wide number of editor contributors of the journal, and some widely known clinicians were given the above question. In other terms what is, in their clinical experience, that matters for the stability of miniscrews.

A number of factors were mentioned:

Experience of the operator
Primary stability - Stable insertion
Self drilling mini-screws
Loading perpendicular to the long axis of the tooth and avoiding unscrewing moments
Quality and thickness of cortical bone, along with wise insertion site selection
Avoidance of root proximity

A wide range of failure rate was suggested, from 5% up to 20% by other clinicians. The whole pdf can be downloaded for free at this link

Hereby follows a quote of what Prof. of Aarhus Denmark, OR department Birte Melsen, DDS, DO answered to the above question:

As chairperson in a graduate program, it is obvious to me that experience is most important for success in the use of skeletal anchorage. Failures are reduced if the doctor refrains from inserting miniscrews where the prognosis is dubious. The quality of bone is the most important factor determining primary stability. According to Dalstra and colleagues the strain obtained by loading a miniscrew perpendicular to the long axis with 50cN leads to loss of primary stability when the cortex is equal to or smaller than .5mm.

Factors related to the insertion procedure: The insertion angle should be kept stable during insertion, and the threaded part should be inserted totally into bone.

Factors related to the screw: We prefer an asymmetrical pitch and a collar that is larger than the threaded section.

Factors related to loading: Loading perpendicular to the long axis is preferable. If the screw is used indirectly by adding a cantilever to a bracket-like head, a force generating a moment around the long axis should be avoided.

With increasing experience, the failure rate of miniscrews can be reduced to around 5%, basically by improving the handling procedure and avoiding skeletal anchorage in situations where the risk is significant.