title: Effects of prestretching on force degradation of synthetic elastomeric chains.
abstract: BACKGROUND
  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 degrees C distilled water. The prestretched and unprestretched (control) modules were then stretched to 30 mm in 37 degrees 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.
authors.affiliation: Department of Orthodontics, College of Dentistry, Yonsei University, Seoul, Korea.
authors.forename: Kyung-Ho
authors.initials: KH
authors.lastname: Kim
authors.forename: Chun-Hsi
authors.initials: CH
authors.lastname: Chung
authors.forename: Kwnagchul
authors.initials: K
authors.lastname: Choy
authors.forename: Jeong-Sub
authors.initials: JS
authors.lastname: Lee
authors.forename: Robert L
authors.initials: RL
authors.lastname: Vanarsdall
mesh_terms: D003799:Dental Stress Analysis / Q000379:methods*; D004548:Elasticity; D020724:Elastomers; D008422:Materials Testing; D009967:Orthodontic Appliances; D010969:Plastics; D013314:Stress, Mechanical; D013718:Tensile Strength; D014087:Tooth Movement Techniques / Q000295:instrumentation*
chemical_list: D020724:Elastomers; D010969:Plastics