title: A comparison of force decay: elastic chain or tie-back method?
abstract: OBJECTIVE
  To evaluate the amount of initial force and to compare the amount of force decay between the elastomeric chain and tie-back method over a period of time.
  
  
  METHODS
  Twenty five-unit elastomeric chains (15 mm) stretched 100%, and twenty elastic modules in tie-back method stretched twice their original diameter were held in place by a series of pins 30-mm apart in acrylic blocks. The blocks were stored in 37 °C distilled water. The force of all samples was measured at baseline, 24 and 48 hours, and once a week thereafter for 4 weeks with a force gauge. The groups were tested with a multivariate analysis of repeated measurement at the 95% confidence level.
  
  
  RESULTS
  The tie-back method with mean force of 577.50 grams (standard deviation [SD] 28.63) had a lower initial force than the elastomeric chain with mean force of 650.00 grams (SD 34.47). The elastomeric chain showed a substantial force decay of 355.50 grams (SD 53.2) at 24 hours, but the force decay in the tie-back method was less (mean 154 grams, SD 56.50). The force decay of the elastomeric chain and tie-back at 48 hours were 446.50 grams (SD 35.4) and 209 grams (SD 57.1), respectively. The difference between the force decay of the two groups at both 24 and 48 hours was statistically significant (P<.05).
  
  
  CONCLUSIONS
  Using the tie-back method of space closure, which has more appropriate initial force and slower force decay, may have a clinical value, approaching a more light and continued force. However, more studies are required to test these findings in vivo.
authors.affiliation: Department of Orthodontics, School of Dentistry, Orthodontic Research Center, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Morteza
authors.initials: M
authors.lastname: Oshagh
authors.forename: Shabnam
authors.initials: S
authors.lastname: Ajami
mesh_terms: D001696:Biomechanical Phenomena; D003764:Dental Materials / Q000737:chemistry*; D020724:Elastomers / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D016382:Orthodontic Appliance Design; D019516:Orthodontic Space Closure / Q000295:instrumentation*; D011140:Polyurethanes / Q000737:chemistry*; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D003764:Dental Materials; D020724:Elastomers; D011140:Polyurethanes; D014867:Water