title: Influence of irradiance on Knoop hardness, degree of conversion, and polymerization shrinkage of nanofilled and microhybrid composite resins.
abstract: The purpose of this study was to investigate the influence of the irradiance emitted by a light-curing unit on microhardness, degree of conversion (DC), and gaps resulting from shrinkage of 2 dental composite resins. Cylinders of nanofilled and microhybrid composites were fabricated and light cured. After 24 hours, the tops and bottoms of the specimens were evaluated via indentation testing and Fourier transform infrared spectroscopy to determine Knoop hardness number (KHN) and DC, respectively. Gap width (representing polymerization shrinkage) was measured under a scanning electron microscope. The nanofilled composite specimens presented significantly greater KHNs than did the microhybrid specimens (P < 0.05). The microhybrid composite resin exhibited significantly greater DC and gap width than the nanofilled material (P < 0.05). Irradiance had a mostly material-dependent influence on the hardness and DC, but not the polymerization shrinkage, of composite resins.
authors.forename: Ana Paula Piovezan
authors.initials: AP
authors.lastname: Fugolin
authors.forename: Lourenço
authors.initials: L
authors.lastname: Correr-Sobrinho
authors.forename: Américo Bortolazzo
authors.initials: AB
authors.lastname: Correr
authors.forename: Mário Alexandre Coelho
authors.initials: MA
authors.lastname: Sinhoreti
authors.forename: Ricardo Danil
authors.initials: RD
authors.lastname: Guiraldo
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
mesh_terms: D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental / Q000009:adverse effects*; D006244:Hardness / Q000528:radiation effects; D058105:Polymerization / Q000528:radiation effects; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D003188:Composite Resins