The quadhelix maxillary expansion appliance: Part I. Mechanics

The mechanics of the quadhelix maxillary expansion appliance have been derived using the complementary (strain) energy approach, and the results checked experimentally on enlarged models. Good agreement between theory and experiment was obtained, for both the lateral stiffness and the magnitude of the molar couple induced. The analysis shows that the spring characteristics are defined by three parameters, the lateral stiffness, and two other parameters M1 phi and M1 y which are the rate of change of the molar couple with phi and y respectively, where phi is the angle the molar arm is rotated on engagement and y the lateral displacement.