title: Morphology and properties of denture acrylic resins cured by microwave energy and conventional water bath.
abstract: OBJECTIVE
  This study examined the influence of microwave energy levels on the morphology and properties of an impact resistant denture material poly(methyl methacrylate) with a thickness of 10 mm.
  
  
  METHODS
  A microwave flask containing two resin blocks was processed at 80, 160, 240, and 560 W for 15, 10, 7, and 2 min, separately. Each Flask was then turned over, and cured for an additional 2 min at 560 W. The process using conventional methods was carried out at 70 degrees C for 9 h. The blocks were tested for hardness, porosity, flexural properties, solubility, and molecular weight. The morphology of the specimens after staining with osmium tetroxide was examined by transmission electron microscope.
  
  
  RESULTS
  The changes in temperature with time were recorded during microwave heating at 80, 160, and 240 W, respectively. A significantly large difference in the curing temperature was observed when comparing these two processing methods. There was little difference in the mean values of surface hardness and the weight percent of the insoluble parts. The mean domain size and the volume fraction of the rubber phase favor of the water-bath method. However, the porosity in the water-bath-cured specimens was much less than that in the microwave-cured specimens. Thus, the conventionally cured specimens showed better flexural strength and flexural modulus than the microwave-cured specimens.
  
  
  CONCLUSIONS
  This study has shown that microwave energy can efficiently polymerize denture base polymer. Highly statistical differences in morphology and flexural properties favor of the water-bath method. Choice of a suitable microwave power and polymerization time is important in order to reduce porosity to a minimum level and increase the domain size and volume of the rubber phase.
authors.affiliation: Institute of Materials Science and Engineering, National Sun Yat-Sen University, 80424 Kaohsiung, Taiwan, ROC.
authors.forename: C-P
authors.initials: CP
authors.lastname: Lai
authors.forename: M-H
authors.initials: MH
authors.lastname: Tsai
authors.forename: M
authors.initials: M
authors.lastname: Chen
authors.forename: H-S
authors.initials: HS
authors.lastname: Chang
authors.forename: H-H
authors.initials: HH
authors.lastname: Tay
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry* / Q000528:radiation effects*; D000704:Analysis of Variance; D002850:Chromatography, Gel; D003799:Dental Stress Analysis; D003819:Denture Bases; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D008854:Microscopy, Electron; D008872:Microwaves; D008970:Molecular Weight; D018583:Pliability; D011108:Polymers / Q000737:chemistry; D016062:Porosity; D012408:Rubber; D012995:Solubility; D013674:Technology, Dental / Q000379:methods; D044366:Transition Temperature; D014867:Water
chemical_list: D000180:Acrylic Resins; D011108:Polymers; D014867:Water; D012408:Rubber