title: Influence of microwave disinfection on the dimensional stability of intact and relined acrylic resin denture bases.
abstract: BACKGROUND
  Microwave irradiation has been suggested as a method to disinfect denture bases. However, the effect of microwave heating on the dimensional stability of the relined denture bases is unknown.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the dimensional stability of intact and relined acrylic resin denture bases after microwave disinfection.
  
  
  METHODS
  A standard brass cast simulating an edentulous maxillary arch was machined and used to fabricate 2- and 4-mm-thick denture bases (n=200), which were processed with heat-polymerized acrylic resin (Lucitone 550). The 2-mm thick-specimens (n=160) were relined with 2 mm of autopolymerizing resin (Tokuso Rebase Fast, Ufi Gel Hard, Kooliner, or New Truliner). Distances between 5 removable pins on the standard brass cast were measured with a Nikon optical comparator, and the area (mm) formed by the distance between 5 pins was calculated and served as baseline. During fabrication, the pins were transferred to the intaglio surface of the specimens. Differences between the baseline area and those subsequently determined for the specimens were used to calculate the percent dimensional changes. The intact and relined denture bases were divided into 4 groups (n=10) and evaluated after: polymerization (control group P); 1 cycle of microwave disinfection (MW); daily microwave disinfection for 7 days (control group MW7); water storage for 7 days (WS7). Microwave irradiation was performed for 6 minutes at 650 W. Data were analyzed using 2-way ANOVA followed by Tukey's test (alpha=.05).
  
  
  RESULTS
  Intact specimens and those relined with Kooliner and New Truliner showed increased shrinkage after 1 (P=.05, .018, and .001, respectively) and 7 (P <.001, .003, and <.001, respectively) cycles of microwave disinfection. With the exception of specimens relined with Kooliner, intact specimens showed greater shrinkage than the relined specimens after 7 cycles of microwave disinfection.
  
  
  CONCLUSIONS
  Microwave disinfection produced increased shrinkage of intact specimens and those relined with New Truliner and Kooliner.
authors.affiliation: Department of Dental Materials and Prosthodontics, Sao Paulo State University, UNESP, Araraquara Dental School, Sao Paulo, Brazil.
authors.forename: Rosangela Seiko
authors.initials: RS
authors.lastname: Seo
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Vergani
authors.forename: Ana Claudia
authors.initials: AC
authors.lastname: Pavarina
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Compagnoni
authors.forename: Ana Lucia
authors.initials: AL
authors.lastname: Machado
mesh_terms: D000180:Acrylic Resins / Q000528:radiation effects; D000704:Analysis of Variance; D003799:Dental Stress Analysis; D003819:Denture Bases; D003822:Denture Liners; D003823:Denture Rebasing; D004203:Disinfection / Q000379:methods*; D008872:Microwaves; D044367:Phase Transition
chemical_list: D000180:Acrylic Resins; C040291:Lucitone