Repetitive prestretching decreases hysteresis and abrupt force drops during the initial unloading phase of orthodontic elastomeric chains

Abstract

This study evaluated the effect of repetitive prestretching on hysteresis and abrupt force drops during the initial unloading phase (1-mm-unloading/peak force ratio) of elastomeric chains. Thirty samples of closed-type elastomeric chains were tested for each group of generation II power chain, energy chain, and memory chain. Elastomeric chains were elongated to a 100% extension from their original length of 12.5 mm and unloaded. Forces during the five loading and unloading cycles were determined. The memory chain showed significantly lower hysteresis than the generation II power chain and energy chain. Both loading and unloading forces were decreased significantly with repetitive prestretching. However, unloading forces decreased less than the loading force, thereby reducing the hysteresis. All three products showed the greatest hysteresis in the first cycle, which decreased significantly following repeated prestretching. The 1-mm-unload/peak ratio increased significantly until the 4th cycle, the cycle after triple prestretching. Conclusively, repetitive prestretching of elastomeric chains further decreased hysteresis and abrupt force drop during the initial 1-mm unloading, up to triple prestretching.