title: Effect of pre- and postpolymerization on flexural strength and elastic modulus of impregnated, fiber-reinforced denture base acrylic resins.
abstract: BACKGROUND
  Impregnated fibers require light polymerization; however, little information exists about how different protocols might affect the mechanical properties of reinforced denture base materials.
  
  
  OBJECTIVE
  The purpose of this study was to compare the effects of pre- or postpolymerization of preimpregnated fibers on the flexural strength and elastic modulus of a reinforced autopolymerized and a heat-polymerized acrylic resin.
  
  
  METHODS
  Seventy-two specimens were divided into 12 treatment groups (n=6), according to type of acrylic resin (autopolymerized or heat polymerized), type of reinforcement, and its pre- or postpolymerization. Impregnated glass fibers (Fibrex-Lab), unimpregnated glass fibers (Fibrante), and ribs made from a restorative composite resin (Z250) were used as reinforcements. The reinforcements were light polymerized either before or after incorporation and processing of the acrylic resins. Specimens were tested in 3-point load and the data were analyzed using 2-way ANOVA and Tukey post hoc test (alpha=.05). Specimens were further examined using light microscopy, atomic force microscopy, and scanning electron microscopy.
  
  
  RESULTS
  Elastic modulus was significantly higher for heat-polymerized acrylic resins than for autopolymerized acrylic resins (P<.001). Prepolymerized fibers increased both flexural strength and elastic modulus of autopolymerized acrylic resins significantly more than postpolymerized fibers (P<.001); however, postpolymerized fibers yielded a higher elastic modulus than prepolymerized fibers for the heat-polymerized material (P<.001).
  
  
  CONCLUSIONS
  Prepolymerized fibers improved the overall mechanical properties of reinforced autopolymerized acrylic resins more than postpolymerized fibers. However, postpolymerization of fibers yielded higher elastic modulus for reinforced heat-polymerized acrylics.
authors.affiliation: Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California, San Francisco, San Francisco, CA 94143-0758, USA. luiz.bertassoni@ucsf.edu
authors.forename: Luiz E
authors.initials: LE
authors.lastname: Bertassoni
authors.forename: Grayson W
authors.initials: GW
authors.lastname: Marshall
authors.forename: Evelise Machado
authors.initials: EM
authors.lastname: de Souza
authors.forename: Rodrigo Nunes
authors.initials: RN
authors.lastname: Rached
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry*; D003799:Dental Stress Analysis; D003819:Denture Bases; D055119:Elastic Modulus; D005898:Glass / Q000737:chemistry; D006244:Hardness; D008422:Materials Testing; D044367:Phase Transition; D018583:Pliability; D055116:Self-Curing of Dental Resins; D013997:Time Factors
chemical_list: D000180:Acrylic Resins; D003188:Composite Resins; C444701:Filtek Z250; C009753:fiberglass