title: Wear resistance of four types of vacuum-formed retainer materials: a laboratory study.
abstract: OBJECTIVE
  To investigate the resistance to wear of four different vacuum-formed retainer (VFR) materials: Essix C+, Essix ACE, Duran, and Tru-Tain. Essix C+ is a polypropylene polymer; the other materials are polyethylene co-polymers.
  
  
  METHODS
  The study was undertaken at the Leeds Dental Institute, Leeds, UK, with 26 samples in each group. The specimens were vacuum-formed according to the manufacturers' guidelines, and a custom-made wear-simulation machine was used to conduct the test. Each specimen was subjected to 1000 cycles of the wear simulation, with steatite balls as the antagonist material. The resistance to wear of the VFR materials was evaluated by measuring the maximum wear depth using noncontact, three-dimensional surface profilometry. The wear depth was given in micrometers.
  
  
  RESULTS
  The median wear depth was 63.20 µm for the Essix C+ group, 7.88 µm for the Essix ACE group, 9.75 µm for the Duran group, and 12.08 µm for the Tru-Tain group. The Kruskal-Wallis test to compare the four VFR materials detected a statistically significant difference between the groups (P < .001). Comparisons of the groups using the Mann-Whitney U-test demonstrated that the Essix C+ group had significantly greater wear than the other three groups (P < .001). There was no statistically significant difference in median wear depth between the two groups with the least amount of wear-the Essix ACE and Duran groups.
  
  
  CONCLUSIONS
  Under the standardized conditions of this laboratory study, the three polyethylene co-polymer materials-Essix ACE, Duran, and Tru-Tain-exhibited significantly less wear than the polypropylene material, Essix C+.
authors.affiliation: a  Specialist Orthodontist, St Luke's Hospital, Bradford, UK.
authors.forename: Taiyub A
authors.initials: TA
authors.lastname: Raja
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Littlewood
authors.forename: Theresa
authors.initials: T
authors.lastname: Munyombwe
authors.forename: Nigel L
authors.initials: NL
authors.lastname: Bubb
mesh_terms: D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008422:Materials Testing; D018613:Microscopy, Confocal / Q000379:methods; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D020959:Polyethylene / Q000737:chemistry; D011126:Polypropylenes / Q000737:chemistry; D013499:Surface Properties; D014618:Vacuum
chemical_list: D003764:Dental Materials; D011126:Polypropylenes; D020959:Polyethylene
keywords: VFR; Vacuum-formed retainer; Wear resistance; Wear test