title: The effect of polymerization cycles on porosity of microwave-processed denture base resin.
abstract: BACKGROUND
  Although most of the physical properties of denture base resin polymerized by microwave energy have been shown to be similar to resins polymerized by the conventional heat polymerization method, the presence of porosity is a problem.
  
  
  OBJECTIVE
  This study evaluated the effect of different microwave polymerization cycles on the porosity of a denture base resin designed for microwave polymerization.
  
  
  METHODS
  Thirty-two rectangular resin specimens (65 x 40 x 5 mm) were divided into 3 experimental groups (A, B, and C; Onda-Cryl, microwave-polymerized resin) and 1 control group (T; Clássico, heat-polymerized resin), according to the following polymerization cycles: (A) 500 W for 3 minutes, (B) 90 W for 13 minutes+500 W for 90 seconds, (C) 320 W for 3 minutes+0 W for 4 minutes+720 W for 3 minutes, and (T) 74 degrees C for 9 hours. Porosity was calculated by measurement of the specimen volume before and after its immersion in water. Data were analyzed using 1-way analysis of variance (alpha=.05).
  
  
  RESULTS
  The mean values and SDs of the percent mean porosity were: A=1.05%+/-0.28%, B=0.91%+/-0.15%, C=0.88%+/-0.23%, T=0.93%+/-0.23%. No significant differences were found in mean porosity among the groups evaluated.
  
  
  CONCLUSIONS
  Within the limitations of this study, a denture base resin specifically designed for microwave polymerization tested was not affected by different polymerization cycles. Porosity was similar to the conventional heat-polymerized denture base resin tested.
authors.affiliation: Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo, Brazil. compagno@foar.unesp.br
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Compagnoni
authors.forename: Debora Barros
authors.initials: DB
authors.lastname: Barbosa
authors.forename: Raphael Freitas
authors.initials: RF
authors.lastname: de Souza
authors.forename: Ana Carolina
authors.initials: AC
authors.lastname: Pero
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry* / Q000528:radiation effects; D000704:Analysis of Variance; D003819:Denture Bases; D006358:Hot Temperature; D006801:Humans; D007101:Immersion; D008422:Materials Testing; D008872:Microwaves; D011108:Polymers / Q000737:chemistry; D016062:Porosity; D013499:Surface Properties; D013997:Time Factors; D014867:Water
chemical_list: D000180:Acrylic Resins; D011108:Polymers; D014867:Water