title: Evaluation of the effect of different stretching patterns on force decay and tensile properties of elastomeric ligatures.
abstract: BACKGROUND
  There have been numerous researches on elastomeric ligatures, but clinical conditions in different stages of treatment are not exactly similar to laboratory conditions. The aim of this in vitro study was to simulate clinical conditions and evaluate the effect of three stretching patterns on the amount of force, tensile strength (TS) and extension to TS of the elastomers during 8 weeks.
  
  
  METHODS
  Forces, TS and extension to TS of two different brands of elastomers were measured at initial, 24 h and 2, 4, and 8-week intervals using a testing machine. During the study period, the elastomers were stored in three different types of jig (uniform stretching, 1 and 3 mm point stretching) designed by the computer-aided design and computer-aided manufacturing technique in order to simulate the different stages of orthodontic treatment.
  
  
  RESULTS
  The elastomeric ligatures under study exhibited a similar force decay pattern. The maximum force decay occurred during the first 24 h (49.9% ± 15%) and the amount of force decay was 75.7% ± 8% after 8 weeks. In general, the TS decreased during the study period, and the amount of extension to TS increased.
  
  
  CONCLUSIONS
  Although the elastic behavior of all ligatures under study was similar, the amount of residual force, TS and extension to TS increased in elastomers under point stretching pattern.
authors.affiliation: Department of Orthodontics, Kerman Dental School, Kerman Oral and Dental Diseases Research Center, Kerman University of Medical Science, Kerman, Iran.
authors.forename: Amin
authors.initials: A
authors.lastname: Aminian
authors.affiliation: Department of Orthodontics, Birjand Dental School, Birjand University of Medical Science, Birjand, Iran.
authors.forename: Samaneh
authors.initials: S
authors.lastname: Nakhaei
authors.affiliation: Oral and Dental Disease Research Center, Kerman University of Medical Sciences, Kerman, Iran.
authors.forename: Raha Habib
authors.initials: RH
authors.lastname: Agahi
authors.affiliation: Department of Mechanical Engineering, Graduate University of Advanced Technology, Kerman, Iran.
authors.forename: Masoud
authors.initials: M
authors.lastname: Rezaeizade
authors.affiliation: Department of Mechanical Engineering, Kerman University of Science, Kerman, Iran.
authors.forename: Hamed Mirzazadeh
authors.initials: HM
authors.lastname: Aliabadi
authors.affiliation: Torabinejad Dental Research Center and Department of Orthodontics, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Majid
authors.initials: M
authors.lastname: Heidarpour
keywords: Elastomeric ligatures; extension to tensile strength; force decay; tensile strength