title: Effect of light-curing units and activation mode on polymerization shrinkage and shrinkage stress of composite resins.
abstract: The aim of this study was to evaluate the polymerization shrinkage and shrinkage stress of composites polymerized with a LED and a quartz tungsten halogen (QTH) light sources. The LED was used in a conventional mode (CM) and the QTH was used in both conventional and pulse-delay modes (PD). The composite resins used were Z100, A110, SureFil and Bisfil 2B (chemical-cured). Composite deformation upon polymerization was measured by the strain gauge method. The shrinkage stress was measured by photoelastic analysis. The polymerization shrinkage data were analyzed statistically using two-way ANOVA and Tukey test (p < or = 0.05), and the stress data were analyzed by one-way ANOVA and Tukey's test (p < or = 0.05). Shrinkage and stress means of Bisfil 2B were statistically significant lower than those of Z100, A110 and SureFil. In general, the PD mode reduced the contraction and the stress values when compared to CM. LED generated the same stress as QTH in conventional mode. Regardless of the activation mode, SureFil produced lower contraction and stress values than the other light-cured resins. Conversely, Z100 and A110 produced the greatest contraction and stress values. As expected, the chemically cured resin generated lower shrinkage and stress than the light-cured resins. In conclusion, The PD mode effectively decreased contraction stress for Z100 and A110. Development of stress in light-cured resins depended on the shrinkage value.
authors.affiliation: Department of Preventive and Oral Reabilitation, Dental School, Federal University of Goiás, Goiânia, GO, Brazil.
authors.forename: Lawrence Gonzaga
authors.initials: LG
authors.lastname: Lopes
authors.forename: Eduardo Batista
authors.initials: EB
authors.lastname: Franco
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Pereira
authors.forename: Rafael Francisco Lia
authors.initials: RF
authors.lastname: Mondelli
mesh_terms: D055598:Chemical Phenomena; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental / Q000145:classification*; D003737:Dental Cavity Preparation / Q000145:classification; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D004853:Epoxy Resins / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D011108:Polymers / Q000737:chemistry / Q000528:radiation effects; D011829:Radiation Dosage; D019279:Resin Cements / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry / Q000528:radiation effects; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D015040:Zirconium / Q000737:chemistry / Q000528:radiation effects
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D004853:Epoxy Resins; C452225:Filtek A110 composite resin; D011108:Polymers; D019279:Resin Cements; C084018:Scotchbond Multi-Purpose; C403464:SureFil packable composite; C083568:Z100 composite resin; C078905:Bisfil; D012822:Silicon Dioxide; D015040:Zirconium