title: The effect of different environmental factors on force degradation of three common systems of orthodontic space closure.
abstract: BACKGROUND
  Different environmental conditions, such as high temperature or exposure to some chemical agents, may affect the force decay of different methods of space closure during orthodontic treatment. The aim of this in vitro study was to evaluate the force decay pattern in the presence of tea as a popular drink in some parts of the world and two mouthwashes that are usually prescribed by the orthodontist once the treatment is in progress.
  
  
  METHODS
  Elastic chain (EC), nickel-titanium (Ni-Ti) closed coil spring and tie-back (TB) method were used as the means of space closure. The specimens were placed in five different media: Hot tea, hot water (65°), chlorhexidine mouthwash, fluoride mouthwash and the control group (water at 37°). The specimens were stretched 25 mm and the elastic force of three systems was measured at the beginning of the study, after 24 h, after 1 week and after 3 weeks. One-way ANOVA was used to compare the results between the groups and Duncan test was carried out to compare the sets of means in different groups (P ≤ 0.05).
  
  
  RESULTS
  Tea increases the force decay in the EC and TB groups. Oral mouthwashes also resulted in more rapid force decay than the control group. EC and Ni-Ti groups were not much affected in the presence of oral mouthwashes.
  
  
  CONCLUSIONS
  Regarding the immersion media, TB method showed the biggest variation in different media and Ni-Ti coil spring was least affected by the type of media.
authors.affiliation: Orthodontic Research Center and Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Morteza
authors.initials: M
authors.lastname: Oshagh
authors.affiliation: Orthodontic Research Center and Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Farzaneh
authors.initials: F
authors.lastname: Khajeh
authors.affiliation: Department of Orthodontic Research Center and Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Bushehr, Iran.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Heidari
authors.affiliation: Orthodontic Research Center and Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Sepideh
authors.initials: S
authors.lastname: Torkan
authors.affiliation: Orthodontic Research Center and Department of Orthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Hamid Reza
authors.initials: HR
authors.lastname: Fattahi
keywords: Elastic chain; environmental factors; force degradation; nickel-titanium coil spring; tie back