[Biomechanic of the asymmetrical headgear]

The asymmetrical headgear is a very useful treatment device for the unilateral distalisation of molars or for the correction of an unilateral anchorage loss. 1. The dimension of the asymmetrical effect depends on the configuration of the outer bows. 2. The function of an asymmetrical face-bow can be increased or decreased by eccentric bendings. 3. According to the geometry at the outer-bows the force at the outer-bow is divided at a different percentage onto the molars. 4. While the forces increase the asymmetrical effect will decrease when the outer-bow is too flexible. 5. Attention has to be payed at each control-appointment to the distance of the longer outer-bow to the cheek. 6. The asymmetrical swivel face-bow did not produce a greater asymmetrical function than other asymmetrical headgears. The reason of this fact is, that only the geometry of the outer-bows is responsible for the unilateral distalisation. 7. The asymmetrical swivel face-bow as described above is advisable to use because eccentric bendings and less forces at the outer-bows will decrease, stop or even reverse the asymmetrical effect. 8. The side-effect of any asymmetrical face-bow is a lateral force-component. This force-component can cause a cross-bite at the molar which has to be more distalized. The molar which is not be moved by the asymmetrical face-bow will be moved buccally by this force-component. 9. The swivel face-bow according to Sander prevents the buccal movement of the molar which should not be moved. But the tendency to create a cross-bite for the molar which should be more distalized, increases. 10. The swivel face-bow according to Sander can be combined with all well-known extraoral tractions. 11. Equal forces at the outer-bows can be reached while using a cervical-pull neckstrap according to Sander. 12. The asymmetrical face-bow and the bite-jumping-appliance can be used simultaneously if the face-bow inserts directly into the attachments of the molar bands.