title: Degree of conversion of composite resin: a Raman study.
abstract: OBJECTIVE
  Near infrared Raman spectroscopy (RS) was used to monitor, in vitro, the degree of conversion (DC) of composite resins (Z100, 3M), photoactivated by both the halogen lamp and the argon laser beam.
  
  
  BACKGROUND
  Several methods were used to study the alterations of composite resins. Vibration methods such as RS allow a precise assessment of the depth of polymerization and the degree of conversion of composite resins.
  
  
  METHODS
  Sixty circular blocks of resin (7 mm x 2.5 mm) were cured using a halogen light source (n=30, lambda=400-500 nm, power density=478 mW/cm2) or an argon laser beam (n=30, lambda=488 nm, power density=625 mW/cm2) using the same irradiation time (5, 10, 20, 30, 40, and 60 sec). The directly irradiated (top) and the non-irradiated (bottom) surfaces were analyzed immediately after curing by Raman spectroscopy.
  
  
  RESULTS
  The Raman results show systematic changes of the relative intensities between the peaks at 1610 (aromatic C=C stretching mode) and the 1640 cm(-1) (methacrylate C=C stretching mode), as a function of irradiation time. After 60 sec of irradiation time, the maximum degree of conversion reached for the samples cured either by the argon laser or halogen lamp was 66.4% and 62.2%, respectively.
  
  
  CONCLUSIONS
  The argon laser was more effective and showed better biocompatibility, with less residual monomer in the bottom (2.5 mm). These results show that RS can be used as an effective method to study the degree of conversion of composite resins.
authors.affiliation: School of Dentistry, Research and Development Institute, IP&D, UNIVAP, São José dos Campos, SP, Brazil. lesoares@univap.br
authors.forename: Luís Eduardo
authors.initials: LE
authors.lastname: Silva Soares
authors.forename: Aírton Abrahão
authors.initials: AA
authors.lastname: Martin
authors.forename: Antonio Luiz
authors.initials: AL
authors.lastname: Barbosa Pinheiro
mesh_terms: D001128:Argon; D003188:Composite Resins / Q000528:radiation effects*; D013059:Spectrum Analysis, Raman
chemical_list: D003188:Composite Resins; D001128:Argon