title: Mechanical properties and polymerization shrinkage of composite resins light-cured using two different lasers.
abstract: OBJECTIVE
  The purpose of the present study was to investigate the usefulness of 457 and 473 nm lasers for the curing of composite resins during the restoration of damaged tooth cavity.
  
  
  BACKGROUND
  Monochromaticity and coherence are attractive features of laser compared with most other light sources. Better polymerization of composite resins can be expected.
  
  
  METHODS
  Eight composite resins were light cured using these two lasers and a light-emitting diode (LED) light-curing unit (LCU). To evaluate the degrees of polymerization achieved, polymerization shrinkage and flexural and compressive properties were measured and compared.
  
  
  RESULTS
  Polymerization shrinkage values by 457 and 473 nm laser, and LED ranged from 10.9 to 26.8, from 13.2 to 26.1, and from 11.5 to 26.3 μm, respectively. The values by 457 nm laser was significantly different from those by 473 and LED LCU (p<0.05). However, there was no statistical difference between values by 473 and LED LCU. Before immersion in distilled water, flexural strength (FS) and compressive modulus (CM) of the specimens were inconsistently influenced by LCUs. On the other hand, flexural modulus (FM) and compressive strength (CS) were not significantly different for the three LCUs (p>0.05). For the tested LCUs, no specific LCU could consistently achieve highest strength and modulus from the specimens tested.
  
  
  CONCLUSIONS
  Two lasers (457 and 473 nm) can polymerize composite resins to the level that LED LCU can achieve despite inconsistent trends of polymerization shrinkage and flexural and compressive properties of the tested specimens.
authors.affiliation: 1 Department of Dental Materials, School of Dentistry and Biomedical Research Institute, Pusan National University , Yangsan, Korea.
authors.forename: Tae-Wan
authors.initials: TW
authors.lastname: Kim
authors.forename: Jang-Hoon
authors.initials: JH
authors.lastname: Lee
authors.forename: Seung-Hwa
authors.initials: SH
authors.lastname: Jeong
authors.forename: Ching-Chang
authors.initials: CC
authors.lastname: Ko
authors.forename: Hyung-Il
authors.initials: HI
authors.lastname: Kim
authors.forename: Yong Hoon
authors.initials: YH
authors.lastname: Kwon
mesh_terms: D003188:Composite Resins / Q000528:radiation effects*; D055117:Curing Lights, Dental; D028022:Low-Level Light Therapy; D058105:Polymerization / Q000528:radiation effects*
chemical_list: D003188:Composite Resins