An investigation into the characteristics of the PG canine retraction spring.

The forces and couples produced by a model of the PG maxillary canine retraction spring (Danish loop) when activated have been derived by using the complementary (strain) energy method. The theoretical results of the analysis have been verified by experiments on enlarged planar models in a special jig that, by means of strain gauges, was capable of recording the forces and couples developed when the models were activated. Good agreement between theory and experiment was obtained that enabled the analysis to be used with confidence to predict the characteristics of clinical-size loops, and to compare the behavior of the PG retractor with some other maxillary canine retraction springs.