title: The effect of fiber orientation on the thermal expansion coefficients of fiber-reinforced composites.
abstract: OBJECTIVE
  The aim of this study was to characterize the thermal expansion and dimensional changes of fiber-reinforced composite (FRC) according to the fiber orientation, brand of FRC product and polymerization conditions.
  
  
  METHODS
  Cubic specimens (n=5) were prepared from different brands of FRC and particulate filler composites and dimethacrylate monomer resin. The specimens were polymerized with a light-curing device for 40 s or additionally with prolonged polymerization in the light-curing oven for 15 min. Linear coefficients of thermal expansion (LCTE) values for different materials and for FRC with different fiber orientations were determined using a thermomechanical analyzer.
  
  
  RESULTS
  All specimens exhibited linear increase in the value of LCTE between 37 and 67 degrees C. The analysis of ANOVA revealed that orientation of fiber and brand of material had significant effect (P<0.001) on LCTE values for 37-67 degrees C interval. Some interaction between factors also existed. Also, temperature interval 110-150 degrees C had significant effect on the LCTE values according to the curing unit, brand and orientation of fibers.
  
  
  CONCLUSIONS
  The results of this study suggest that the anisotropic nature of FRC exists also with regard to thermal expansion. The variation of LCTE of FRC compared to that of particulate filler composites might influence the interfacial adhesion of FRC appliances.
authors.affiliation: Department of Prosthetic Dentistry and Biomaterials Research, Institute of Dentistry, University of Turku, Lemminkäisenkatu 2, 20520 Turku, Finland. arztez@utu.fi
authors.forename: Arzu
authors.initials: A
authors.lastname: Tezvergil
authors.forename: Lippo V J
authors.initials: LV
authors.lastname: Lassila
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
mesh_terms: D000704:Analysis of Variance; D016880:Anisotropy; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D004055:Differential Thermal Analysis; D005898:Glass; D006358:Hot Temperature; D008422:Materials Testing
chemical_list: D003188:Composite Resins; C009753:fiberglass