Force system developed from closed coil springs.

The present paper provides data on load-deflection rate and maximal force generated for 19 coil springs. The force level at activation and deactivation was registered at intervals of 5 mm between 0 and 100 per cent extension. Ten springs of each type were analysed. The following questions were answered. How many of the springs exhibited the behaviour of a superelastic spring and how many types of springs differed significantly from each other with respect to force deflection rate and maximal force level at 100 per cent extension? Of the products tested only the springs from GAC exhibited the behaviour characteristic of the superelastic wire. The 19 products could, from a clinical point of view, be classified into four different groups with regard to force deflection rate and five groups with regard to maximal force. The variation within each product also differed between the products with the lowest intra-product variation seen in the TP springs. In light of the present findings it is obvious that manufacturers' information was not satisfactory. The need for more thorough user information is stressed.