title: Effects of mechanical properties of thermoplastic materials on the initial force of thermoplastic appliances.
abstract: OBJECTIVE
  To measure the forces delivered by thermoplastic appliances made from three materials and investigate effects of mechanical properties, material thickness, and amount of activation on orthodontic forces.
  
  
  METHODS
  Three thermoplastic materials, Duran (Scheu Dental), Erkodur (Erkodent Erich Kopp GmbH), and Hardcast (Scheu Dental), with two different thicknesses were selected. Values of elastic modulus and hardness were obtained from nanoindentation measurements at 28°C. A custom-fabricated system with a force sensor was employed to obtain measurements of in vitro force delivered by the thermoplastic appliances for 0.5-mm and 1.0-mm activation for bodily tooth movement. Experimental results were subjected to several statistical analyses.
  
  
  RESULTS
  Hardcast had significantly lower elastic modulus and hardness than Duran and Erkodur, whose properties were not significantly different. Appliances fabricated from thicker material (0.75 mm or 0.8 mm) always produced significantly greater force than those fabricated from thinner material (0.4 mm or 0.5 mm). Appliances with 1.0-mm activation produced significantly lower force than those with 0.5-mm activation, except for 0.4-mm thick Hardcast appliances. A strong correlation was found between mechanical properties of the thermoplastic materials and force produced by the appliances.
  
  
  CONCLUSIONS
  Orthodontic forces delivered by thermoplastic appliances depend on the material, thickness, and amount of activation. Mechanical properties of the polymers obtained by nanoindentation testing are predictive of force delivery by these appliances.
authors.affiliation: Division of Orthodontics and Dentofacial Orthopedics, Department of Oral Growth and Development, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido, Japan.
authors.forename: Naohisa
authors.initials: N
authors.lastname: Kohda
authors.forename: Masahiro
authors.initials: M
authors.lastname: Iijima
authors.forename: Takeshi
authors.initials: T
authors.lastname: Muguruma
authors.forename: William A
authors.initials: WA
authors.lastname: Brantley
authors.forename: Karamdeep S
authors.initials: KS
authors.lastname: Ahluwalia
authors.forename: Itaru
authors.initials: I
authors.lastname: Mizoguchi
mesh_terms: D000704:Analysis of Variance; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006244:Hardness; D008422:Materials Testing; D003765:Models, Dental; D016382:Orthodontic Appliance Design / Q000379:methods*; D010969:Plastics / Q000737:chemistry*; D014087:Tooth Movement Techniques / Q000295:instrumentation*
chemical_list: D010969:Plastics