title: Influence of light-polymerization modes on the degree of conversion and mechanical properties of resin composites: a comparative analysis between a hybrid and a nanofilled composite.
abstract: This study analyzed the influence of the light polymerization mode on the degree of conversion (DC) and mechanical properties of two resin composites: a hybrid (Filtek P60) and a nanofilled composite (Filtek Supreme). The composites were light activated by three light polymerization modes (Standard-S: 650 mW/cm2 for 30 seconds; High intensity-H: 1000 mW/cm2 for 20 seconds and Gradual-G: 100 up to 1000 mW/cm2 for 10 seconds + 1000 mW/cm2 for 10 seconds). The DC (%) was measured by FT-Raman spectroscopy. Flexural strength and flexural modulus were obtained from bar-shaped specimens (1 x 2 x 10 mm) submitted to the three-point bending test. Microhardness was evaluated by Knoop indentation (KHN). Data were analyzed by ANOVA and Student-Newman-Keuls multiple range test and linear regression analysis. The results showed the following DC: H > S > G (p < 0.0001) and hybrid > nanofilled (p < 0.005). Correlation was found between DC and the radiant exposure (R2 = 0.92). With respect to mechanical properties, only KHN was significantly influenced by the light polymerization mode, as follow: H > S = G (p < 0.0001). The hybrid composite presented higher flexural strength and flexural modulus than the nanofilled composite (p < 0.0001). No significant difference was found in KHN between thetwo composites (p = 0.1605). The results suggest that nanofilled composites may present a lower degree of conversion and reduced mechanical properties compared to hybrid composites.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Federal Fluminense University, Rua São Paulo, RJ, Brazil. emsilva@vm.uff.br
authors.forename: Eduardo Moreira
authors.initials: EM
authors.lastname: da Silva
authors.forename: Laiza Tatiana
authors.initials: LT
authors.lastname: Poskus
authors.forename: José Guilherme Antunes
authors.initials: JG
authors.lastname: Guimarães
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D004548:Elasticity; D006244:Hardness; D006801:Humans; D008027:Light; D008422:Materials Testing; D053758:Nanoparticles / Q000737:chemistry* / Q000528:radiation effects; D018583:Pliability; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013314:Stress, Mechanical; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C438835:Filtek P60 Composite Resin; C474035:Filtek Supreme; D011108:Polymers