title: Polymerization shrinkage stress of composites photoactivated by different light sources.
abstract: The purpose of this study was to compare the polymerization shrinkage stress of composite resins (microfilled, microhybrid and hybrid) photoactivated by quartz-tungsten halogen light (QTH) and light-emitting diode (LED). Glass rods (5.0 mm x 5.0 cm) were fabricated and had one of the surfaces air-abraded with aluminum oxide and coated with a layer of an adhesive system, which was photoactivated with the QTH unit. The glass rods were vertically assembled, in pairs, to a universal testing machine and the composites were applied to the lower rod. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The 20 composites were polymerized by either QTH (n=10) or LED (n=10) curing units. Polymerization was carried out using 2 devices positioned in opposite sides, which were simultaneously activated for 40 s. Shrinkage stress was analyzed twice: shortly after polymerization (t40s) and 10 min later (t10min). Data were analyzed statistically by 2-way ANOVA and Tukey's test (alpha=5%). The shrinkage stress for all composites was higher at t10min than at t40s, regardless of the activation source. Microfilled composite resins showed lower shrinkage stress values compared to the other composite resins. For the hybrid and microhybrid composite resins, the light source had no influence on the shrinkage stress, except for microfilled composite at t10min. It may be concluded that the composition of composite resins is the factor with the strongest influence on shrinkage stress.
authors.affiliation: Department of Dental Materials and Prosthodontics, Ribeirão Preto Dental School, University of São Paulo, Ribeirão Preto, SP, Brazil. ferpanzeri@forp.usp.br
authors.forename: Fernanda de Carvalho Panzeri
authors.initials: Fde C
authors.lastname: Pires-de-Souza
authors.forename: Brahim
authors.initials: B
authors.lastname: Drubi Filho
authors.forename: Luciana Assirati
authors.initials: LA
authors.lastname: Casemiro
authors.forename: Lucas da Fonseca Roberti
authors.initials: Lda F
authors.lastname: Garcia
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry / Q000528:radiation effects; D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental / Q000145:classification*; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D003799:Dental Stress Analysis; D017220:Dentin-Bonding Agents / Q000737:chemistry / Q000528:radiation effects; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D053758:Nanoparticles / Q000737:chemistry / Q000528:radiation effects; D011140:Polyurethanes / Q000737:chemistry / Q000528:radiation effects; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects; D018709:Statistics, Nonparametric
chemical_list: D000180:Acrylic Resins; C084111:Charisma composite resin; D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; C466112:Esthet-X; C513708:Heliomolar; D011140:Polyurethanes; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose