title: Influence of microwave polymerization method and thickness on porosity of acrylic resin.
abstract: OBJECTIVE
  This study evaluated the influence of polymerization cycle and thickness of maxillary complete denture bases on the porosity of acrylic resin.
  
  
  METHODS
  Two heat-activated denture base resins--one conventional (Clássico) and one designed for microwave polymerization (Onda-Cryl)--were used. Four groups were established, according to polymerization cycles: A (Onda-Cryl, short microwave cycle), B (Onda-Cryl, long microwave cycle), C (Onda-Cryl, manufacturing microwave cycle), and T (Clássico, water bath). Porosity was evaluated for different thicknesses (2.0, 3.5, and 5.0 mm; thicknesses I, II, and III, respectively) by measurement of the specimen volume before and after its immersion in water. The percent porosity data were submitted to Kruskal-Wallis for comparison among the groups.
  
  
  RESULTS
  The Kruskal-Wallis test detected that the combinations of the different cycles and thicknesses showed significant differences, and the mean ranks of percent porosity showed differences only in the thinnest (2.0 mm) microwave-polymerized specimens (A = 53.55, B = 40.80, and C = 90.70). Thickness did not affect the results for cycle T (I = 96.15, II = 70.20, and III = 82.70), because porosity values were similar in the three thicknesses.
  
  
  CONCLUSIONS
  Microwave polymerization cycles and the specimen thickness of acrylic resin influenced porosity. Porosity differences were not observed in the polymerized resin bases in the water bath cycle for any thickness.
authors.affiliation: Graduate Student, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, BrazilAssistant Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, São Paulo State University, Araçatuba, São Paulo, BrazilAssociate Professor, Department of Chemistry, São Carlos Federal University, São Carlos, BrazilAssociate Professor, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
authors.forename: Ana Carolina
authors.initials: AC
authors.lastname: Pero
authors.affiliation: Graduate Student, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, BrazilAssistant Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, São Paulo State University, Araçatuba, São Paulo, BrazilAssociate Professor, Department of Chemistry, São Carlos Federal University, São Carlos, BrazilAssociate Professor, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
authors.forename: Débora Barros
authors.initials: DB
authors.lastname: Barbosa
authors.affiliation: Graduate Student, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, BrazilAssistant Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, São Paulo State University, Araçatuba, São Paulo, BrazilAssociate Professor, Department of Chemistry, São Carlos Federal University, São Carlos, BrazilAssociate Professor, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
authors.forename: Juliê
authors.initials: J
authors.lastname: Marra
authors.affiliation: Graduate Student, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, BrazilAssistant Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, São Paulo State University, Araçatuba, São Paulo, BrazilAssociate Professor, Department of Chemistry, São Carlos Federal University, São Carlos, BrazilAssociate Professor, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
authors.forename: Adhemar Colla
authors.initials: AC
authors.lastname: Ruvolo-Filho
authors.affiliation: Graduate Student, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, BrazilAssistant Professor, Department of Dental Materials and Prosthodontics, Araçatuba Dental School, São Paulo State University, Araçatuba, São Paulo, BrazilAssociate Professor, Department of Chemistry, São Carlos Federal University, São Carlos, BrazilAssociate Professor, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Compagnoni
mesh_terms: D000042:Absorption; D000180:Acrylic Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D003819:Denture Bases; D003827:Denture, Complete, Upper; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008872:Microwaves; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D019904:Polymethyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D016062:Porosity; D011312:Pressure; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D003764:Dental Materials; D011108:Polymers; D014867:Water; D019904:Polymethyl Methacrylate