title: [Mechanical properties of thermoplastic materials].
abstract: OBJECTIVE
  To investigate the mechanical properties of various brands of thermoplastic materials under different test conditions so as to analyze their influencing factors so as to provide a reference for improving the effect of invisible orthodontics.
  
  
  METHODS
  Three brands of thermoplastic materials, DR, Biolon and Erkodent, were selected. They were tested by Instron testing machine to measure their maximal stress and modulus under different processing modes, including pre-thermoforming, post-thermoforming and dipped in artificial saliva for two weeks after thermoforming. The data were analyzed by SPSS 11.5. Analyzed the mechanical properties change-trend under each test condition.
  
  
  RESULTS
  The modulus (MPa) and maximum stress (MPa) of control group were significantly higher than those of thermoforming group (DR: 9.63±0.68 vs 7.85±0.61, 267±8 vs 199±6; Erkodent: 8.28±0.28 vs 7.59±0.45, 226±6 vs 199±6; Biolon: 8.85±0.41 vs 7.07±0.22, 237±6 vs 169±7, all P<0.05). The modulus (MPa) and maximum stress (MPa) of thermoforming group were significantly lower than those of saliva immersion group (DR: 7.85±0.61 vs 9.14±0.41, 199±6 vs 243±7; Erkodent: 7.59 ± 0.45 vs 8.38±0.29, 199±6 vs 212±7; Biolon: 7.07±0.22 vs 7.90±0.31, 169±7 vs 197±5, all P<0.05).
  
  
  CONCLUSIONS
  The different brands of thermoplastic materials have different mechanical properties. The different processing modes influence the mechanical properties of thermoplastic materials. The mechanical properties decrease after thermoforming and increase after saliva immersion.
authors.affiliation: Department of Orthodontics, School of Stomatology, Capital Medical University, Beijing 100050, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Yu-xing
authors.initials: YX
authors.lastname: Bai
authors.forename: Kun-ya
authors.initials: KY
authors.lastname: Zhang
mesh_terms: D055119:Elastic Modulus; D008422:Materials Testing; D009967:Orthodontic Appliances; D013314:Stress, Mechanical