title: Polymerization development of "low-shrink" resin composites: Reaction kinetics, polymerization stress and quality of network.
abstract: OBJECTIVE
  To evaluate "low-shrink" composites in terms of polymerization kinetics, stress development and mechanical properties.
  
  
  METHODS
  "Low-shrink" materials (Kalore/KAL, N'Durance/NDUR, and Filtek P90/P90) and one control (Esthet X HD/EHD) were tested. Polymerization stress (PS) was measured using the Instron 5565 tensometer. Volumetric shrinkage (VS) was determined by the ACTA linometer. Elastic modulus (E) and flexural strength (FS) were obtained by a three-point bending test. Degree of conversion (DC) and polymerization rate (Rp) were determined by NIR spectroscopy (6165cm(-1) for dimethacrylates; 4156 and 4071cm(-1) for P90). Photopolymerization was performed at 740mW/cm(2)×27s. Glass transition temperature (Tg), degree of heterogeneity and crosslink density were obtained in a DMA for the fully cured specimens. Analysis of extracts was done by (1)H NMR. Data were analyzed with one-way ANOVA/Tukey's test (α=0.05).
  
  
  RESULTS
  The control presented the highest shrinkage and Tg. P90 showed the highest modulus, and NDUR demonstrated the highest conversion. The polymerization rates were comparable for all materials. NDUR and KAL had the highest and the lowest network homogeneity, respectively. The multifunctional P90 had the highest crosslink density, with no difference between other composites. The control had the greatest stress development, similar to NDUR. Crosslinking density and polymer network homogeneity were influenced by degree of conversion and monomer structure.
  
  
  CONCLUSIONS
  Not all "low-shrink" composites reduced polymerization stress. P90 and NDUR had no leachable monomers, which was also a function of high crosslinking (P90) and high conversion (NDUR).
authors.affiliation: Department of Biomaterials and Oral Biology, University of São Paulo, School of Dentistry, São Paulo, SP, Brazil. liyamasaki@uol.com.br
authors.forename: Lilyan C
authors.initials: LC
authors.lastname: Yamasaki
authors.forename: André G
authors.initials: AG
authors.lastname: De Vito Moraes
authors.forename: Mathew
authors.initials: M
authors.lastname: Barros
authors.forename: Steven
authors.initials: S
authors.lastname: Lewis
authors.forename: Carlos
authors.initials: C
authors.lastname: Francci
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Stansbury
authors.forename: Carmem S
authors.initials: CS
authors.lastname: Pfeifer
mesh_terms: D000465:Algorithms; D003188:Composite Resins / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D053761:Nanocomposites / Q000737:chemistry; D018583:Pliability; D058105:Polymerization; D011140:Polyurethanes / Q000737:chemistry; D062047:Silorane Resins / Q000737:chemistry; D019265:Spectroscopy, Near-Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D044366:Transition Temperature
chemical_list: D003188:Composite Resins; D003432:Cross-Linking Reagents; D003764:Dental Materials; C466112:Esthet-X; D008689:Methacrylates; C551012:N'Durance composite resin; D011140:Polyurethanes; D062047:Silorane Resins; C544925:filtek P90; C555513:silorane composite resin; C029824:urethane dimethacrylate luting resin
keywords: Composite; Degree of conversion; Dynamic mechanical analysis; Extraction study; Polymerization kinetics; Polymerization stress; Silorane