title: Microwave disinfection: cumulative effect of different power levels on physical properties of denture base resins.
abstract: OBJECTIVE
  This study evaluated the cumulative effects of different microwave power levels on the physical properties of two poly(methylmethacrylate) (PMMA) denture base resins.
  
  
  METHODS
  Eight sets of four PMMA specimens each (two polymerized in a water bath and two using microwave energy) were immersed in beakers containing 200 ml of distilled water. Each beaker was subjected to microwave irradiation for 3 minutes at a power level of 450,630, or 900 W. The surface roughness, surface hardness, linear stability, flexural strength, elastic modulus, impact strength, and fractographic properties were evaluated after either 6 or 36 simulated disinfection cycles. The data were statistically analyzed using ANOVA and the Tukey post hoc test (α= 0.05).
  
  
  RESULTS
  The polymerization method did not influence any property (p > 0.05) except linear stability. The surface roughness (p < 0.001) and hardness (p= 0.011) increased after 36 irradiation cycles at 630 or 900 W. The resin polymerized using microwave energy exhibited greater linear distortion (p= 0.012), and there was a cumulative effect on linear stability for both resins (p < 0.001). No significant change (p > 0.05) was observed in flexural strength; however, the elastic modulus decreased (p= 0.008) after 36 disinfection cycles. The impact strength and crack propagation angles displayed no significant differences (p > 0.05).
  
  
  CONCLUSIONS
  Within the limitations of this study, it can be concluded that microwave disinfection at 450 W to 630 W for 3 minutes is safe for PMMA.
authors: Department of Prosthodontics and Periodontology, Piracicaba Dental School, State University of Campinas, Piracicaba, Brazil. psenna3@fop.unicamp.br
authors: Plinio M
authors: PM
authors: Senna
authors: Wander Jose
authors: WJ
authors: Da Silva
authors: Fernanda
authors: F
authors: Faot
authors: Altair Antoninha
authors: AA
authors: Del Bel Cury
mesh_terms: D003799:Dental Stress Analysis; D003819:Denture Bases; D004203:Disinfection / Q000379:methods*; D055119:Elastic Modulus; D006244:Hardness; D008422:Materials Testing; D008872:Microwaves; D018583:Pliability; D058105:Polymerization; D019904:Polymethyl Methacrylate / Q000528:radiation effects*; D013499:Surface Properties
chemical_list: D019904:Polymethyl Methacrylate