Effects of prestretching on force degradation of synthetic elastomeric chains

Introduction: The purpose of this study was to evaluate the effects of prestretching on time-dependant force decay of synthetic elastomeric chains. Methods: Five-unit (12.5 mm) and 6-unit (15.5 mm) modules (Generation II, Ormco, Glendora, Calif) were prestretched 100% for 1 hour (n = 12), 24 hours (n = 12), 2 weeks (n = 12), and 4 weeks (n = 12) in 37°C distilled water. The prestretched and unprestretched (control) modules were then stretched to 30 mm in 37°C water, and their forces were measured at 0 hour, 1 hour, 24 hours, and weekly for 4 weeks with a digital force gauge. Results: The prestretched 5- and 6-unit modules yielded significantly lower initial force than the controls. All 5- and 6-unit prestretched and control groups showed substantial force decay during the first hour. However, at 1 hour, similar remaining forces were found in the 5-unit prestretched and control groups (P > .05), and small differences were seen in the 6-unit groups. The rates and patterns of force decay from 1 hour to 4 weeks were quite similar between the control and the prestretched modules of both the 5- and 6-unit groups. Conclusions: The effects of prestretching on force decay of elastomeric chains were noted mainly in the first hour. Thus, the clinical value of prestretching a synthetic elastomeric chain is questionable.