title: Chemical and mechanical characteristics of contemporary thermoplastic orthodontic materials.
abstract: OBJECTIVE
  The aim of the present study was to characterise the chemical and mechanical properties of contemporary thermoplastic orthodontic materials.
  
  
  METHODS
  Four thermoplastic materials were tested: Clear Aligner (Scheu-Dental), ACE and A+ (Dentsply), and Invisalign (Align Technology). Eight appliances were fabricated from each material and a small portion from each was analysed by ATR-FTIR spectroscopy. The appliances were cut and, following metallographic grinding and polishing, were subjected to instrumented indentation testing (IIT) employing a Vickers indenter. Martens Hardness (HM), Indentation Modulus (E(IT)), Elastic to Total Work Ratio (elastic index (η(IT))) and Indentation Creep (C(IT)) were determined according to ISO 14577-1. The mean values of the mechanical properties were statistically analysed by one way ANOVA and Tukey Kramer multiple comparison test at a = 0.05.
  
  
  RESULTS
  ATR-FTIR analysis identified that Invisalign was a polyurethane-based material, whereas the others were based on polyester, polyethylene glycol terephthalate (PETG). Invisalign showed higher hardness and modulus values, a slightly higher brittleness and lesser creep resistance compared with the PETG-based products.
  
  
  CONCLUSIONS
  The materials tested showed significant differences in their chemical structure and mechanical properties and therefore differences in their clinical behaviour are anticipated.
authors.forename: Alexandros
authors.initials: A
authors.lastname: Alexandropoulos
authors.forename: Youssef S
authors.initials: YS
authors.lastname: Al Jabbari
authors.forename: Spiros
authors.initials: S
authors.lastname: Zinelis
authors.forename: Theodore
authors.initials: T
authors.lastname: Eliades
mesh_terms: D055598:Chemical Phenomena; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing / Q000379:methods; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D009967:Orthodontic Appliances; D010969:Plastics / Q000737:chemistry*; D011091:Polyesters / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011093:Polyethylene Terephthalates / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013314:Stress, Mechanical
chemical_list: D003764:Dental Materials; D010969:Plastics; D011091:Polyesters; D011093:Polyethylene Terephthalates; D011140:Polyurethanes; C475920:polyethylene terephthalate glycol; D011092:Polyethylene Glycols