title: Shrinkage stress and degree of conversion of a dental composite submitted to different photoactivation protocols.
abstract: The aim of this study was to evaluate the polymerization stress and degree of conversion of a composite submitted to different photoactivation protocols. The composite Filtek Z350 was placed in the central perforation of a photoelastic disc and polymerized using a LED-based curing unit (BluePhase II--Ivoclar Vivadent) with energy density of 12, 24 or 36 J/cm2 using the following photopolymerization protocols: continuous high intensity (HI: 1200 mW/cm2 during 10, 20 or 30s), continuous low intensity (LI: 650 mW/cmz during 18, 36 or 54s) and soft-start (SS: 150 mW/cm2 during 5 s + 1200 mW/cm2 during 9, 19 or 29s) (n = 5). Photoelastic analysis was used to evaluate polymerization shrinkage stress and FTIR was performed to determine the degree of conversion of the composite. ANOVA 3-way procedure was used to determine the significance of the main effects and their interactions followed by two-way ANOVA for each time was performed (p < 0.05). Shrinkage stress increased with higher values of energy. No statistically significant differences on polymerization shrinkage stress were found between high and low intensity activation modes. Soft-start method generated stresses that were statistically lower than continuous modes except when 12 J/cm2 was applied. Similar degree of conversion was observed for photoactivation modes used, except for soft-start mode with 12, 24 and 36J/cm2 that showed lowest levels of conversion. Energy density and activation mode influenced polymerization shrinkage stress, but no benefit on degree of conversion was observed.
authors.affiliation: Department of Dental Materials, Piracicaba Dental School, State University of Campinas, SP, Brazil. karlamychellyne@yahoo.com.br
authors.forename: Karla M C
authors.initials: KM
authors.lastname: Oliveira
authors.forename: Ailla C R A
authors.initials: AC
authors.lastname: Lancellotti
authors.forename: Renzo A
authors.initials: RA
authors.lastname: Ccahuana-Vásquez
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
mesh_terms: D003188:Composite Resins; D003799:Dental Stress Analysis; D008027:Light; D008422:Materials Testing; D058105:Polymerization
chemical_list: D003188:Composite Resins