title: Color stability and hardness in dental composites after accelerated aging.
abstract: OBJECTIVE
  To investigate the color and microhardness changes of five chemically- and five light-curing composites as a function of accelerated aging from light exposure.
  
  
  METHODS
  From each material five composite specimens were embedded in epoxy resin prior to determining the Knoop microhardness of the surface. For analyzing the color DeltaE*=f((L*a*b*)) with a spectrophotometer, three discs per composite were prepared. After measuring the baseline for hardness and color the same specimens were exposed to a xenon arc light and water in a Weather-Ometer machine for a total radiant energy of 150 kJ/m2 and 122 h. The microhardness and the color were again determined following the aging treatment.
  
  
  RESULTS
  Each material showed a significant increase in hardness after aging treatment (p<0.05). Comparing the hardness changes (in %) of the light-cured materials with the chemically cured materials, no significant difference could be found. Perceptible color differences could be observed for all the materials. Three brands showed small differences with DeltaE*=1.6-2.2, while four composites had DeltaE* ranging from 6.2 to 15.5. A significant correlation between hardness values and color changes could not be established.
  
  
  CONCLUSIONS
  The findings suggest that, since light-curable materials showed significantly more resistance to color changes after accelerated aging by light and water than chemically-cured materials, they may be more esthetically acceptable. Color changes were not correlated with surface hardness changes of the materials after aging.
authors.affiliation: Department of Preventive and Restorative Dental Sciences, Division of Biomaterials and Bioengineering, University of California San Francisco, 707 Parnassus Avenue, Box 0758, San Francisco, CA 94143-0758, USA.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Schulze
authors.forename: Sally J
authors.initials: SJ
authors.lastname: Marshall
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Gansky
authors.forename: Grayson W
authors.initials: GW
authors.lastname: Marshall
mesh_terms: D000704:Analysis of Variance; D003116:Color; D003188:Composite Resins; D019554:Dental Restoration Wear; D003799:Dental Stress Analysis; D006244:Hardness; D006358:Hot Temperature; D006813:Humidity; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D018709:Statistics, Nonparametric; D014867:Water
chemical_list: D003188:Composite Resins; D011108:Polymers; D014867:Water