title: [Effect of light power density on the anti-aging property of light-cure composite resin].
abstract: OBJECTIVE
  The purpose of this study was to investigate the effect of light power density on anti-aging property of composite resins.
  
  
  METHODS
  Three light curing modes with different power density (1. Mode A: low power density, 500 mW/cm(2) for 22 s; 2. Mode B: high power density, 1 100 mW/cm(2) for 10 s; 3. Mode C: gradually enhanced power density, 0~650 mW/cm(2) for 5 s + 1 100 mW/cm(2) for 8.5 s) were used. The total energy density of these modes was all 11 J/cm(2). Composite resin specimens were cured with three light curing modes respectively and divided into 4 groups randomly (n=15). Three groups were reserved in absolute ethanol for 24 h, 7 d and 30 d respectively for aging and one group was stored in water for 24 h as control. Vicker hardness (VHN) was measured with microhardness tester. Volumetric shrinkage was measured with Acuvol (n=7).
  
  
  RESULTS
  The hardness of three light curing modes was: Mode A 44.26±6.16, Mode B 42.31±2.33 and Mode C 45.60±2.76. After aging in ethanol for 24 h, the hardness of all composites specimen decreased (P<0.05). Samples cured by Mode A (31.83±2.90) and Mode C (32.13±2.77) showed significantly lower hardness than Mode B (36.14±2.65) (P<0.05). After aging in ethanol for 7 d, the hardness of composites continuously decreased (P<0.05) and was: Mode A 28.36±2.35, Mode B 27.80±1.19 and Mode C 28.20±0.97. There was no significant difference among three curing modes (P>0.05). The hardness of samples stored in ethanol for 30 d was no longer decreased and was: Mode A 28.53±0.86, Mode B 28.55±1.53 and Mode C 29.08±1.60. There was no significant difference between composite specimen stored for 7 d and 30 d (P>0.05). The polymerization shrinkage of composite resin was: Mode A 2.67%±0.28%, Mode B 2.76%±0.29% and Mode C 2.73%±0.06%. No significant difference existed among polymerization shrinkage of composites cured by the three light curing modes with different power density (P>0.05).
  
  
  CONCLUSIONS
  The power density of curing light affected the anti-aging property of composite resin which was aging time dependent. The polymerization shrinkage was not affected by light power density with same energy density.
authors.affiliation: Department of Cariology and Endodontology, Peking University School and Hospital of Stomatology, Beijing 100081, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Han
authors.forename: Xiao yan
authors.initials: Xy
authors.lastname: Wang
authors.forename: Xue jun
authors.initials: Xj
authors.lastname: Gao
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental; D003793:Dental Restoration, Permanent / Q000145:classification / Q000379:methods*; D003799:Dental Stress Analysis; D008027:Light; D008422:Materials Testing
chemical_list: D003188:Composite Resins