title: Effect of the physical properties of acrylic resin of overnight immersion in sodium hypochlorite solution.
abstract: OBJECTIVE
  This study evaluated colour stability, surface roughness and flexural strength of microwave-polymerised acrylic resin after overnight immersion in sodium hypochlorite, simulating 180 days use.
  
  
  METHODS
  Forty disc-shaped (15 mm x 4 mm) and 40 rectangular specimens (65 mm x 10 mm x 3 mm) were prepared from microwave-polymerised acrylic resin. The specimens were immersed in 0.5, 1% sodium hypochlorite, Clorox/Calgon and distilled water. Colour measurements (ΔE) were determined by a portable colorimeter. A surface analyser was used to measure roughness (μm). The flexural strength (MPa) was measured using a three-point bending test in a universal testing machine. Data were evaluated by one-way anova, followed by Student-Newman-Keuls test (α = 0.05).
  
  
  RESULTS
  Statistical analysis found significantly higher colour changes (SNK, p < 0.001) for the 1% sodium hypochlorite, but mean ΔE value quantified by National Bureau of Standards was classified as slight. When comparing the surface roughness, no statistical significance was found among the solutions (anova, p = 0.637). The 1% sodium hypochlorite presented significantly lower flexural strength compared with the control group (SNK, p = 0.034).
  
  
  CONCLUSIONS
  It was concluded that immersion in 1% sodium hypochlorite solutions for 8 h does influence the colour stability and flexural strength of microwave-polymerised acrylic resin, during the simulated period of 180 days.
authors.affiliation: Department of Dental Materials and Prosthodontics, Ribeirão Preto School of Dentistry, University of São Paulo, Ribeirão Preto, Brazil. leticiadavi@hotmail.com
authors.forename: Letícia Resende
authors.initials: LR
authors.lastname: Davi
authors.forename: Amanda
authors.initials: A
authors.lastname: Peracini
authors.forename: Nathália de Queiroz
authors.initials: Nde Q
authors.lastname: Ribeiro
authors.forename: Rafael Bellini
authors.initials: RB
authors.lastname: Soares
authors.forename: Cláudia Helena Lovato
authors.initials: CH
authors.lastname: da Silva
authors.forename: Helena de Freitas Oliveira
authors.initials: Hde F
authors.lastname: Paranhos
authors.forename: Raphael Freitas
authors.initials: RF
authors.lastname: de Souza
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D055598:Chemical Phenomena; D003116:Color; D003124:Colorimetry; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003902:Detergents / Q000737:chemistry; D004202:Disinfectants / Q000737:chemistry*; D006801:Humans; D007101:Immersion; D008422:Materials Testing; D008872:Microwaves; D010710:Phosphates / Q000737:chemistry; D018583:Pliability; D058105:Polymerization; D012973:Sodium Hypochlorite / Q000737:chemistry*; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000180:Acrylic Resins; D003764:Dental Materials; D003902:Detergents; D004202:Disinfectants; D010710:Phosphates; D012973:Sodium Hypochlorite; C009285:sodium polymetaphosphate