title: Polymerization shrinkage of restorative resins using laser and visible light curing.
abstract: OBJECTIVE
  This in vitro investigation compared the amount of linear shrinkage that occurs when a light-cured composite resin is cured with a visible light source, and also with an argon laser.
  
  
  BACKGROUND
  When composite resins are light-cured, they undergo a certain degree of polymerization shrinkage, which can be clinically significant and affect the efficacy of the restoration. A new protocol utilizes laser curing instead of conventional visible light.
  
  
  METHODS
  Two hybrid composite resins were used, Z100 and TPH-Spectrum. Dimensional change was measured in a linear direction, using a calibrated light-microscope. A total of 40 samples of composite resin was tested using two curing lights, and two hybrid composite resins, resulting in four groups of 10 samples (n = 10) each. According to manufacturer instructions, curing time for the laser was 10 sec, and for visible light was 40 sec.
  
  
  RESULTS
  With TPH-Spectrum, the mean shrinkage with visible light was 0.583% compared to that with laser light which was 0.591%. With Z100, the mean shrinkage with visible light was 0.565%, compared to that with laser light which was 0.551%.
  
  
  CONCLUSIONS
  There was no significant difference in amount of shrinkage of hybrid composite resins between using visible light or laser light. There was also no significant difference in shrinkage between the two hybrid composites for either light source.
authors.affiliation: School of Dentistry, University of Washington, Seattle 98195, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Aw
authors.forename: J I
authors.initials: JI
authors.lastname: Nicholls
mesh_terms: D000704:Analysis of Variance; D001128:Argon; D003188:Composite Resins / Q000737:chemistry*; D007834:Lasers; D008027:Light; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D011108:Polymers; C088833:Prisma TPH resin composite; C083568:Z100 composite resin; D001128:Argon; D012822:Silicon Dioxide; D015040:Zirconium