RESUMO
Expansion screws such as Hyrax and Hass have high load-activation rate and their force system is somehow far from ideal for moving teeth. Hence, activation of such screws produces heavy forces that decay rapidly. Also, rapid reactivation of the appliance has the potential of damaging the teeth and periodontium. Moreover, lack of patient's cooperation in activation of screw could be considered as one of its main disadvantages. The purpose of this investigation was to assess and compare the force- activation curve of a designed screw with those of the commonly used expansion screws. In this experimental study, a screw was designed and manufactured in similar size as the other screws with the potential of 8 millimeter expansion in 2 times activation. The screw was embedded in acrylic material in a removable appliance and fixed on its plaster cast. The compression test machine was used to depict its load-activation curve. The curve was compared with other screws' curves. The results of this study showed that the designed screw had a lower load-deflection rate than other screws. It generated a light continuous force of 2- 3.5 pounds for 4 millimeter expansion. Compared with other screws which produce heavy and interrupted forces, the designed screw generated a light continuous force