title: Force delivery properties of thermoplastic orthodontic materials.
abstract: BACKGROUND
  Our objectives were to evaluate the force and energy (resilience) delivery properties of thermoplastic overlay orthodontic materials and to determine the changes in force delivery properties after thermocycling or repeated load cycling.
  
  
  METHODS
  Three types and 3 thicknesses of materials were investigated. Three-point bending-recovery tests were performed at baseline and after cycling procedures. For cycling, the specimens were thermocycled for 1000 cycles or repeatedly deflected by 1 mm for 100 cycles. Vickers hardness was measured to determine the changes after thermocycling or repeated load cycling.
  
  
  RESULTS
  The amount of deflection for optimal force delivery was 0.2 to 0.5 mm. Thin material exerted high energy in the deflection range of optimal force delivery. In the deflection ranges of optimal force delivery (0.2-0.5 mm), the force delivery properties after thermocycling were not different from those at the baseline (P >.01) but were different after repeated load cycling (P <.01). Thermocycling and repeated load cycling influenced Vickers hardness significantly.
  
  
  CONCLUSIONS
  Thin material (0.508 mm) can deliver higher energy than thick materials (0.762 or 1.016 mm, P <.01) of the same brand. Therefore, thin material should be selected in the same brand of material. The effect of repeated deflection during service should be considered.
authors.affiliation: Department of Dental Biomaterial Science, College of Dentistry, Seoul National University, Seoul, Korea.
authors.forename: Jae-Sung
authors.initials: JS
authors.lastname: Kwon
authors.forename: Yong-Keun
authors.initials: YK
authors.lastname: Lee
authors.forename: Bum-Soon
authors.initials: BS
authors.lastname: Lim
authors.forename: Yong-Kyu
authors.initials: YK
authors.lastname: Lim
mesh_terms: D000704:Analysis of Variance; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D006358:Hot Temperature; D008422:Materials Testing; D016382:Orthodontic Appliance Design; D009968:Orthodontic Appliances, Removable; D018583:Pliability; D011126:Polypropylenes; D011145:Polyvinyls; D018709:Statistics, Nonparametric; D014087:Tooth Movement Techniques
chemical_list: D011126:Polypropylenes; D011145:Polyvinyls; C016438:ethylenevinylacetate copolymer