title: Effect of time and polymerization cycle on the degree of conversion of a resin composite.
abstract: The aim of this investigation was to verify the influence of 3 light curing units on the degree of conversion, using different irradiation conditions: 1) manufacturers' recommended times of photo-activation, 2) standardizing total energy density among the units and 3) standardizing energy density at the 450-490 nm wavelength range among the units and the effect of these irradiation conditions on the post-cure. Three light curing units were used: halogen, light emitting diodes (LED) and xenon plasma. Seven groups were tested (n=6). Twenty-four hours after the photo-activation procedures, half of the composite specimens were submitted to Fourier Transformed Infrared Spectroscopy analysis. The other half was analyzed after 1 month. The results were submitted to 2-way ANOVA and Tukey's test (5%). Twenty-four hour analysis revealed that the second set of irradiation conditions produced a similar degree of conversion among the LCUs. After 1 month, the conversion values were statistically higher for 20 seconds of halogen exposure (increased from 46.78 to 49.66%), 20 seconds of LED exposure (from 46.20 to 51.15%), 30 seconds of LED exposure (from 48.29% to 50.68%) and 3 seconds of PAC exposure (from 42.57 to 51.39%). The initial degree of conversion and post-cure depended on the photo-activation condition applied.
authors.affiliation: Dental Materials Area, Piracicaba Dental School, State University of Campinas (UNICAMP), Brazil.
authors.forename: Luis Felipe Jochims
authors.initials: LF
authors.lastname: Schneider
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
authors.forename: Fabrício
authors.initials: F
authors.lastname: Ogliari
authors.forename: Américo Bortolazzo
authors.initials: AB
authors.lastname: Correr
authors.forename: Lourenço Correr
authors.initials: LC
authors.lastname: Sobrinho
authors.forename: Mário Alexandre Coelho
authors.initials: MA
authors.lastname: Sinhoreti
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D008027:Light; D008029:Lighting / Q000295:instrumentation; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D011874:Radiometry; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C444701:Filtek Z250; D011108:Polymers