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A modification to the standard quadhelix transpalatal expansion arch is presented in which the wire passes distal to the most posterior molar and enters the mesial end of the headgear tube. Laboratory measurements were carried out on small, average and large sized appliances with this modification using a special rig fitted with strain gauges. For the three sizes of appliance, the modified quadhelix is more flexible than the standard quadhelix for both displacement and rotation of the molar arms. Also it is less time consuming to fit and remove it is concluded that this appliance is capable of producing clinically useful forces and couples with increased precision.

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