title: Flexural strength and hardness of reline and denture base acrylic resins after different exposure times of microwave disinfection.
abstract: OBJECTIVE
  To evaluate the effect of microwave disinfection on the flexural strength and Vickers hardness of 4 autopolymerized resins (Kooliner [K], Tokuso Rebase Fast [T], Ufi Gel Hard [U], and New Truliner [N]) and 1 denture base resin (Lucitone 550 [L]).
  
  
  METHODS
  For each material, 48 specimens (64 x 10 x 3.3 mm) were made and divided into 6 equal groups (n = 8). In the control group, specimens were untreated. Before testing, specimens were immersed in 200 mL of distilled water and submitted to disinfection for 1 of the following irradiation times: 1, 2, 3, 4, or 5 minutes. The irradiation procedure was performed twice. The flexural strength was determined using a testing machine MTS-810 and measurements of Vickers hardness were made on Micromet 2100. The values were submitted to ANOVA and Tukey's test (P = .05).
  
  
  RESULTS
  The K material showed a significant increase (P = .0010) in flexural strength following 5 minutes of disinfection compared to control specimens. The flexural strength mean values of materials T, U, and N were not significantly affected (P > .05) by disinfection. Compared to the control group, the K material showed a significant increase in hardness (P < .001) following disinfection for 3, 4, and 5 minutes. For material U, disinfection for 4 and 5 minutes produced specimens with significantly increased hardness values (P < .001) compared to the control group. For material N, disinfection for 5 minutes resulted in significantly higher hardness values (P < .001) than the control group.
  
  
  CONCLUSIONS
  Regardless of the irradiation time, the flexural strength and hardness of the materials evaluated were not detrimentally affected by microwave disinfection.
authors.affiliation: Department of Dental Materials and Prosthodontics, São Paulo State University, UNESP, Araraquara Dental School, São Paulo, Brazil.
authors.forename: Daniela Garcia
authors.initials: DG
authors.lastname: Ribeiro
authors.forename: Ana Cláudia
authors.initials: AC
authors.lastname: Pavarina
authors.forename: Ana Lucia
authors.initials: AL
authors.lastname: Machado
authors.forename: Eunice Teresinha
authors.initials: ET
authors.lastname: Giampaolo
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Vergani
mesh_terms: D000180:Acrylic Resins / Q000528:radiation effects; D003799:Dental Stress Analysis; D003819:Denture Bases; D003822:Denture Liners; D004203:Disinfection / Q000379:methods*; D006244:Hardness; D019552:Infection Control, Dental / Q000379:methods*; D008422:Materials Testing; D008872:Microwaves; D018583:Pliability; D011897:Random Allocation; D013997:Time Factors
chemical_list: D000180:Acrylic Resins