The quadhelix maxillary expansion appliance: Part II: Clinical characteristics

In a previous paper (Jones and Waters, 1989) a theoretical model of the quadhelix was developed and tested against enlarged models. Good agreement was obtained. In this paper the theoretical model has been used to examine the effect, on the lateral stiffness and molar couple characteristics, of altering the size of the appliance's various components within the clinical size range. It is suggested that the wide variation in the force-deflection characteristics found by previous authors could be explained by differences in appliance dimensions.