title: Hardness of heat-polymerized acrylic resins after disinfection and long-term water immersion.
abstract: BACKGROUND
  In selecting a disinfectant for dental prostheses, compatibility between the disinfectant and the type of denture base material must be considered to avoid adverse effects on the hardness of the acrylic resin.
  
  
  OBJECTIVE
  This study investigated the hardness of 2 denture base resins after disinfection and long-term water immersion.
  
  
  METHODS
  Thirty-two disk-shaped specimens (13 mm in diameter and 8 mm thick) were fabricated from each resin (Lucitone 550 and QC-20), polished, stored in water at 37 degrees C for 48 hours, and submitted to hardness tests (Vickers hardness number [VHN]) before disinfection. Disinfection methods included scrubbing with 4% chlorhexidine gluconate for 1 minute, immersion for 10 minutes in 1 of the tested disinfectant solutions (n=8) (3.78% sodium perborate, 4% chlorhexidine gluconate, or 1% sodium hypochorite), and immersion in water for 3 minutes. The disinfection procedures were repeated 4 times, and 12 hardness measurements were made on each specimen. Control specimens (not disinfected) were stored in water for 56 minutes. Hardness tests (VHN) were also performed after 15, 30, 60, 90, and 120 days of storage in water. Statistical analyses of data were conducted with a repeated measures 3-way analysis of variance (ANOVA) and Tukey post-hoc test (alpha=.05).
  
  
  RESULTS
  Mean values +/- SD for Lucitone 550 (16.52 +/- 0.94 VHN) and QC-20 (9.61 +/- 0.62 VHN) demonstrated a significant (P <.05) decrease in hardness after disinfection, regardless of material and disinfectant solutions used (Lucitone 550: 15.25 +/- 0.74; QC-20: 8.09 +/- 0.39). However, this effect was reversed after 15 days of storage in water. Both materials exhibited a continuous increase (P <.05) in hardness values for up to 60 days of water storage, after which no significant change was observed.
  
  
  CONCLUSIONS
  Within the limitations of this in vitro study, QC-20 and Lucitone 550 specimens exhibited significantly lower hardness values after disinfection regardless of the disinfectant solution used.
authors.affiliation: Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, C.E.P. 14801-1903, Brazil.
authors.forename: Karin Hermana
authors.initials: KH
authors.lastname: Neppelenbroek
authors.forename: Ana Cláudia
authors.initials: AC
authors.lastname: Pavarina
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: Vergani
authors.forename: Eunice Teresinha
authors.initials: ET
authors.lastname: Giampaolo
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D001881:Borates / Q000494:pharmacology; D002710:Chlorhexidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004202:Disinfectants / Q000494:pharmacology; D004203:Disinfection / Q000379:methods; D006244:Hardness; D006358:Hot Temperature; D008422:Materials Testing / Q000379:methods; D012973:Sodium Hypochlorite / Q000494:pharmacology; D014867:Water / Q000494:pharmacology
chemical_list: D000180:Acrylic Resins; D001881:Borates; D004202:Disinfectants; C488492:QC 20 (denture base resin); D014867:Water; C040291:Lucitone; D012973:Sodium Hypochlorite; C010882:chlorhexidine gluconate; D002710:Chlorhexidine; C027707:sodium perborate