title: Effect of accelerated aging on the color and opacity of resin cements.
abstract: BACKGROUND
  The color stability of resin cements plays a major role in the esthetic performance of porcelain laminate veneers. Some dual-polymerizable resin cements used to bond porcelain laminates were shown to undergo color changes during service. Some recently produced cements are described as being color stable, but scientific data are not available.
  
  
  OBJECTIVE
  The current study evaluated the effect of accelerated aging on the color and opacity of resin cements. The hypothesis was that the auto-polymerizing cements would show less color and opacity stability.
  
  
  METHODS
  Forty (0.7 x 18 mm) feldspathic porcelain disks were prepared and divided into four equal groups. The resin cements were bonded to the disks by application of an identical load of 2.5 kilograms, and they were polymerized according to the manufacturer's instructions. The groups were: Variolink Veneer (light-polymerizing), Variolink II (light-polymerizing), Variolink II (dual-polymerizing) and Multilink (auto-polymerizing). A spectrophotometer was used to measure the following color parameters in the CIE L*a*b* color space on a black and white background: deltaa*, deltab*, deltaL*, deltaC, deltaH, deltaE and deltaCR (contrast ratio). The measurements were performed before and after aging. Paired t- and one-way ANOVA tests were used to analyze the data (alpha = .05).
  
  
  RESULTS
  None of the groups showed significant differences in deltaE before and after aging (p > .05); deltaE remained in the range of clinical acceptance (deltaE < 3.3). All of the cements became more opaque, while deltaCR (difference in contrast ratio) was significantly different (p = .004). The auto-polymerized cement showed an increase in opacity.
  
  
  CONCLUSIONS
  The studied cements behaved acceptably according to deltaE, but they became more opaque after aging.
  
  
  CONCLUSIONS
  The studied cements can ensure color stability when used to cement porcelain laminate veneers, but the change in opacity can affect clinical results. Auto polymerizing cements become more opaque with aging; therefore, porcelain restorations may lose their match with other teeth.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Tehran University of Medical Sciences, Dental Research Center, Tehran, Iran. maghavam@gmail.com
authors.forename: Maryam
authors.initials: M
authors.lastname: Ghavam
authors.forename: Mohammad
authors.initials: M
authors.lastname: Amani-Tehran
authors.forename: Mahshid
authors.initials: M
authors.lastname: Saffarpour
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D003116:Color; D055117:Curing Lights, Dental / Q000145:classification; D001840:Dental Bonding; D003776:Dental Porcelain / Q000737:chemistry; D003801:Dental Veneers; D004955:Esthetics, Dental; D006801:Humans; D006813:Humidity; D008027:Light; D008422:Materials Testing; D058105:Polymerization; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D013053:Spectrophotometry; D013696:Temperature; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D017680:Potassium Compounds; D019279:Resin Cements; C502351:multilink adhesive system; D003776:Dental Porcelain; C016447:feldspar; C103502:Variolink