title: Polymerization contraction stress of low-shrinkage composites and its correlation with microleakage in class V restorations.
abstract: OBJECTIVE
  The aim of this study was to compare the behavior of two new, low-shrinkage hybrid composites (Aelite LS and Inten-S) with a microfilled (Heliomolar) and a hybrid composite (Filtek Z250), in terms of polymerization contraction stress and microleakage.
  
  
  METHODS
  Maximum contraction stress after 10 min was recorded in a "tensilometer", using a C-factor (C) of 2.5 and energy density of 26 J/cm(2). For the microleakage test, cylindrical cavities with enamel margins prepared in bovine incisors (4 mm diameter, 1.5 mm depth, C = 2.5) were restored in bulk, applying the same energy density used in the contraction stress test. After immersion in 0.5% methylene blue for 4 h, specimens were sectioned twice, perpendicularly, and the highest dye penetration score was recorded. Contraction stress results were analyzed by one-way ANOVA/Tukey's test and microleakage was analyzed by Kruskal-Wallis test. Regression analysis between the two variables was also performed.
  
  
  RESULTS
  Aelite LS showed significantly higher stress than the other composites tested. Inten-S and Filtek Z250 had similar stress levels, statistically higher than Heliomolar. In the microleakage test, a significant difference was observed between Aelite LS and Heliomolar only. Regression analysis showed a good linear correlation between the two variables (R2(adjusted) = 0.811).
  
  
  CONCLUSIONS
  The low-shrinkage materials exhibited contraction stress values similar or higher than the hybrid composite. A direct relationship between contraction stress values and microleakage for the composites evaluated was verified.
  
  
  CONCLUSIONS
  The low-shrinkage composites tested did not seem to represent an improvement in terms of reducing contraction stress or microleakage.
authors.affiliation: Department of Dental Materials, School of Dentistry, University of São Paulo, 2227 São Paulo, SP 05508-900, Brazil.
authors.forename: Fernanda Calabró
authors.initials: FC
authors.lastname: Calheiros
authors.forename: Fernanda Tranchesi
authors.initials: FT
authors.lastname: Sadek
authors.forename: Roberto Ruggiero
authors.initials: RR
authors.lastname: Braga
authors.forename: Paulo Eduardo Capel
authors.initials: PE
authors.lastname: Cardoso
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D000818:Animals; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation / Q000145:classification*; D003743:Dental Enamel / Q000648:ultrastructure; D003763:Dental Leakage / Q000145:classification*; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent / Q000145:classification*; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D012044:Regression Analysis; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D013499:Surface Properties
chemical_list: D000180:Acrylic Resins; C485363:Aelite LS; C029012:Composite Dental Resin; D003188:Composite Resins; C444701:Filtek Z250; C513708:Heliomolar; C485362:InTen-S composite; D008689:Methacrylates; D011108:Polymers; D011140:Polyurethanes; D017438:Bisphenol A-Glycidyl Methacrylate