title: Effect of 457 nm diode-pumped solid state laser on the polymerization composite resins: microhardness, cross-link density, and polymerization shrinkage.
abstract: OBJECTIVE
  The purpose of the present study was to test the usefulness of 457 nm diode-pumped solid state (DPSS) laser as a light source to cure composite resins.
  
  
  METHODS
  Five different composite resins were light cured using three different light-curing units (LCUs): a DPSS 457 nm laser (LAS), a light-emitting diode (LED), and quartz-tungsten-halogen (QTH) units. The light intensity of LAS was 560 mW/cm(2), whereas LED and QTH LCUs was ∼900 mW/cm(2). The degree of polymerization was tested by evaluating microhardness, cross-link density, and polymerization shrinkage.
  
  
  RESULTS
  Before water immersion, the microhardness of laser-treated specimens ranged from 40.8 to 84.7 HV and from 31.7 to 79.0 HV on the top and bottom surfaces, respectively, and these values were 3.3-23.2% and 2.9-31.1% lower than the highest microhardness obtained using LED or QTH LCUs. Also, laser-treated specimens had lower top and bottom microhardnesses than the other LCUs treated specimens by 2.4-19.4% and 1.4-27.8%, respectively. After ethanol immersion for 24 h, the microhardness of laser-treated specimens ranged from 20.3 to 63.2 HV on top and bottom surfaces, but from 24.9 to 71.5 HV when specimens were cured using the other LCUs. Polymerization shrinkage was 9.8-14.7 μm for laser-treated specimens, and these were significantly similar or lower (10.2-16.0 μm) than those obtained using the other LCUs.
  
  
  CONCLUSIONS
  The results may suggest that the 457 nm DPSS laser can be used as a light source for light-curing dental resin composites.
authors.affiliation: 1 Department of Conservative Dentistry, School of Dentistry, Pusan National University , Yangsan, Korea.
authors.forename: Sung-Ae
authors.initials: SA
authors.lastname: Son
authors.forename: Jeong-Kil
authors.initials: JK
authors.lastname: Park
authors.forename: Kyoung-Hwa
authors.initials: KH
authors.lastname: Jung
authors.forename: Ching-Chang
authors.initials: CC
authors.lastname: Ko
authors.forename: Chang-Mo
authors.initials: CM
authors.lastname: Jeong
authors.forename: Yong Hoon
authors.initials: YH
authors.lastname: Kwon
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D055117:Curing Lights, Dental; D006244:Hardness; D053844:Lasers, Solid-State; D008422:Materials Testing; D058105:Polymerization
chemical_list: C084111:Charisma composite resin; D003188:Composite Resins; C444701:Filtek Z250; C452441:Synergy composite resin; C121818:Tetric ceram; C533204:filtek Z350