A mechanical study of asymmetric face-bows for unilateral molar distalization

YOSHIDA,Noriaki, KOGA,Yoshiyuki, ABE,Risako, KOBAYASHI,Kazuhide, SASAKI,Hiromitsu, ARAMAKI,Gunji

The aim of this study was to clarify the effects of asymmetric face-bow and to discuss an appropriate design and/or the methods whereby the side effect of this appliance can be reduced. The force systems acting on the molars under the application of various designs of asymmetric face-bow, whose outer bows on one side were extended or expanded laterally, were determined by means of framed structure analysis. Then the influence of changes in face-bow's design on the molar movements was analyzed. It was concluded as follows ; 1. An attempt to provide more effective asymmetric molar distalization by increasing asymmetry of the face-bow is accompanied by an increase of lateral forces, which lead to a crossbite of the molar. 2. Almost the same magnitude of moments in the bucco-mesial direction were produced on bilateral molars regardless of the face-bow's design or degree of asymmetry. Therefore, the asymmetry of the degree of rotation of the right and left molars is not thought to increase during the treatment, although it has been considered as another side effect of asymmetric face-bow. 3. It is recommendable to avoid using exceedingly asymmetric face-bow, since its side effect may be critical. The present study proposes using a face-bow. whose outer bow end is located at a point corresponding to the face-bow tube on one side and contralateral outer bow is extended 25 to 30 mm distally or extended 15 mm distally and then expanded 30 mm laterally on the side, in which the molar should be more distalized.

A mechanical study of asymmetric face-bows for unilateral molar distalization

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